How to perform a compression test on legacy 2-stroke outboards like Mercury 2.5L, Johnson, Yamaha, and Evinrude 2-stroke outboards. Performing a compression test on a legacy 2-stroke outboard is one of the best ways to diagnose internal engine health. Whether you’re working on a Mercury 2.0L, 2.4L, 2.5L, 3.0L, or a classic OMC, Johnson, Evinrude, or Yamaha, a compression test reveals how well each cylinder is sealing and helps guide decisions about rebuilds, tuning, and also fuel octane choice. Unlike four-stroke engines, these two-strokes use intake, exhaust, transfer, and sometimes finger ports cut into the cylinder walls. Compression doesn’t start until the piston closes the exhaust port, which means cranking compression values vary significantly with port design, timing, and application. Some engines use behind-the-liner porting, particularly Mercury’s high-performance blocks, which route the intake charge through channels behind the sleeves and in the block. These aggressive port layouts reduce static compression readings but increase high-RPM performance. That’s why there are no universal factory compression specs. What matters more is consistency across cylinders and interpreting values in the context of engine design. Testing Procedures To properly test compression, warm up the engine, disable the ignition, and remove all spark plugs. Install the gauge in one cylinder at a time, crank the engine several times, and record the peak PSI. Repeat for each cylinder. All cylinders should be within about 10 PSI of each other. Use a warm engine and fully open throttle for best results. Now, interpreting results depends on the application. Compression under 90 PSI usually signals that a rebuild is necessary. In many Mercury and Yamaha outboards, 90–100 PSI is borderline. The engine might run, but it’s tired. 100–120 PSI is considered decent for a stock or lightly used recreational engine. 120–140 PSI typically means a strong, well-sealing motor. Anything over 140 PSI suggests a high-performance setup, and you must run premium octane fuel to avoid detonation. Engines reading 155+ PSI are usually race builds and require race fuel, avgas, or a blend, or risk piston damage. If the readings are low across all cylinders but consistent, a hone and new rings might restore compression. If one cylinder is significantly lower, you could be dealing with a broken ring, scored bore, or a sealing issue, which might require a bore and a new piston(s). Always inspect bores and pistons to confirm. All exhaust and intake ports require extra care in chamfering the ports during rebuilds to prevent ring snagging. 🔧 Compression Test Summary 0-90 PSI  – Rebuild required: likely worn rings or scored bore. 90–100 PSI  – Borderline: engine may run but is tired, expect rebuild soon. 100–120 PSI  – OK for recreational use: typical for older stock motors. 120–140 PSI  – Strong engine: good sealing, run premium (91+) octane fuel. 145-155 PSI  – High-performance build: must run premium (93+) or race fuel. 155-210 PSI  – Race motor territory: use race fuels or blends (96+) octane. ✅ Always check that all cylinders are within 10 PSI of each other. ⚠️ Mismatched readings or a single low hole may indicate a ring, port, or piston issue. ⛽ Match fuel octane to compression—high PSI needs high-octane to avoid detonation. ⏱️ Timing  – Keep ignition timing at 25° BTDC or less , unless tuning for a race setup. The timing guidance provided here (25 degrees BTDC or less) applies specifically to Mercury 2.0, 2.4, and 2.5-liter 2-stroke engines. For other motor models, always refer to the factory timing specifications. Optimax and DFI Outboards Compression testing an Optimax differs from legacy 2-strokes due to its direct injection system and recessed spark plugs, which may require special adapters. Normal readings are lower—typically 90–110 PSI. Under 80 PSI suggests mechanical issues; higher may indicate carbon buildup or test error. Disable the ECU and injectors to avoid interference. Optimax engines also rely on an air compressor to deliver high-pressure air to the injectors—low air pressure can mimic low compression symptoms. For accurate diagnosis, combine compression testing with air and fuel pressure checks, leakdown, and injector testing. Compression testing isn’t just about numbers. It’s about knowing what those numbers mean for your specific build. From Johnson crossflows to Yamaha loopers, from a tired fishing motor to a Mercury 2.5L race setup, compression is telling us all something. Listen carefully and see what she needs. Resources Download our 2-stroke compression test guide, free online in PDF. Most compression gauges will work on these motors. Here is a reasonably priced one we use.

A Century of Speed and Innovation: Honoring Paul O’Neil Allison and the Legacy of Allison Craft Boats . The marine racing world mourns the passing of a true American original. Paul O’Neil Allison, visionary inventor, artist, and co-founder of Allison Craft Boats, passed away peacefully on May 7, 2025, at the age of 100. For more than six decades, Paul was a leader in boatbuilding, a pioneer of racing innovation, and a beloved figure in both his industry and community. His legacy lives on in every hull design, propeller tweak, and racing team still chasing the speeds he helped make possible. The Allison Legacy: A Family Tradition Rooted in Craftsmanship The Allison family’s journey in boatbuilding began long before fiberglass, outboards, or competitive drag racing. In 1917, Paul’s father, Rev. James Allison, built the very first Allison boat. That spirit of craftsmanship passed to Paul, whose own story began in earnest in 1955 when he was given a rotten wooden boat. He salvaged the hardware and used it to construct his first racing hull—a sleek, handcrafted vessel that outperformed anything he had previously raced. Encouraged by early success and recovering from a life-altering hunting injury, Paul decided to leave his auto body business behind and pursue boatbuilding full-time. That same year, he and his wife Lucille, his partner in life and work for 76 years, founded Allison Craft Boats in Friendsville, Tennessee. Record-Breaking Speeds and the Rise of Allison Craft Boats By 1959, Paul had built his last wooden boat—but not before making history. That year, he became the first to break 60 miles per hour in a production outboard pleasure boat, setting a straightaway speed record of 61.8 mph with just an 80-horsepower motor. This breakthrough would define the Allison legacy: fast, efficient, and engineered for excellence. In 1960, with fiberglass technology emerging in marine construction, Paul designed and built his first 14-foot fiberglass boat. This lighter, faster, and more aerodynamic craft became the foundation for decades of high-performance innovation. The Allison team’s appetite for speed only grew. Throughout the 1960s and 1970s, Paul’s boats continued to set new benchmarks: 1962 – Surpassed 70 mph 1964 – Surpassed 80 mph 1968 – Surpassed 90 mph 1969 – Surpassed 100 mph (twin engines) 1975 – Surpassed 110 mph 1984 – Surpassed 120 mph 1987 – Reached 129+ mph These were not experimental race machines—they were real boats, using production components, pushing boundaries year after year. Engineering Innovations That Redefined the Water Paul Allison wasn’t just building boats—he was shaping the very future of performance boating. From the 1950s through the 1980s, he pioneered a number of now-standard marine technologies that forever changed how high-performance boats were built and handled. In the 1950s, he introduced the cupped propeller, a revolutionary change that improved bite and control at high speeds, eventually catching the attention of Carl Kiekhaefer at Mercury Marine. Around the same time, Paul also developed the first hydraulic power trim, allowing for dynamic control of boat attitude under throttle. The 1960s saw Paul’s development of the first V-bottom hull with a pad, which dramatically improved lift and tracking—particularly at high speed and during acceleration. This design remains foundational in bass boat hull architecture to this day. During the 1970s, Paul took marine aerodynamics even further. He introduced wing stabilizers, front foils for tunnel boats, and the cupped skeg—each contributing to better lift, reduced drag, and precise tracking under extreme performance conditions. Paul’s relentless experimentation became legendary. On many early mornings, he could be found at a Tennessee boat ramp, applying Bondo to the bottom of a test hull, making temporary shape changes, running test passes, then chipping or sanding the material off to evaluate the results. These hands-on techniques were years ahead of their time and didn’t go unnoticed. One of those who observed Paul firsthand was Rourk Summerford, who would go on to found both Laser Boats and STV Boats (Summerford Tunnel Vee) after working. As a young man, Summerford watched Paul at those ramps with admiration, witnessing his process of refining bottom designs in real-time. The experience left a lasting impression. In tribute to Paul’s impact on his life and career, Rourk named one of his daughters Allison—a heartfelt nod to the man who helped shape his future in racing and performance boat design. OPC and APBA: The Golden Age of Racing The 1960s and 1970s marked the golden age of OPC racing—Outboard Pleasure Craft, which later evolved into Outboard Performance Craft—and Paul’s boats were at the heart of the action. Under the sanction of the American Power Boat Association (APBA), Allison Craft boats became a dominant force. What made OPC racing special was its accessibility. Enthusiasts could walk into a dealership, buy a production Allison Craft boat, pair it with a stock Mercury, Johnson, or Evinrude outboard, and head straight to the racecourse. Competitors raced in popular classes such as E Class, G Class, Family Sport (FS), and Family J (FJ)—and Allison boats were consistently at the front of the pack. This era showcased not just the speed of Paul’s designs, but also their reliability, handling, and pure racing DNA. Drag Boat Racing: The Next Frontier In the early 1980s, Mod VP and drag boat racing rose in popularity, demanding a different type of performance—one that emphasized acceleration over handling. Allison Craft Boats met the moment, once again becoming the vessel of choice for serious racers. Their lightweight construction, aerodynamic efficiency, and hallmark pad-bottom hulls helped racers consistently hit triple-digit speeds down the quarter mile. From casual showdowns to sanctioned national events, Allison drag boats are still to this day feared, revered, and nearly unbeatable in the hands of skilled pilots. A Life Beyond the Water: Family, Farming, and Friends Paul’s contributions weren’t confined to propellers and hulls. He and Lucille also operated Allison’s Catfish Restaurant, a beloved local landmark that reflected the same family values and attention to quality that made their boats famous. He was also a gifted artist, known for his attention to detail and love of creative expression. At home on his farm, Paul’s favorite pastime was building waterfalls and digging in the dirt with his Bobcat—a joy he carried into his later years with childlike enthusiasm. Paul was preceded in death by Lucille and his parents, Rev. James and Ressie Allison. He is survived by his children—Darris (Nancy), Denise (Mike), Danette (Steve), and Donna (Donnie)—as well as a large and loving family of grandchildren, great-grandchildren, nieces, nephews, and countless friends from both the racing and restaurant communities. Honoring a Legend: Tributes Across the Racing World Paul’s influence continues to be felt in race pits and boat garages across the country. Racers and fans like Buckshot Racing #77, and countless others, are paying tribute to the man whose designs helped them reach new levels of speed, safety, and competitive excellence. Whether racing bass boats, OPC, Mod VP tunnel hulls, or drag boats, competitors knew one thing: if it was built by Allison, it was built to win.

Managing Overvoltage in Mercury High-Performance 2-Stroke V6 Outboards with Billet Flywheels Mercury’s high-performance 2-stroke V6 outboards—particularly the 2.0L, 2.4L, and 2.5L models including the XR2, XR4, XR6, 150, 175, 200, 225 Pro Max horsepower variants, along with race motors like the 260 EFI Offshore, 300 Drag, S3000, and SST120—are built for high-RPM operation, often spinning well beyond 7,200 RPM. Many of these engines rely on a 16-amp charging system to minimize rotational mass and reduce parasitic drag, critical for maximum throttle response and performance. However, when these motors are modified with aftermarket billet flywheels containing rare-earth magnets, significant and potentially damaging overvoltage issues can occur—particularly if the charging system remains unregulated. From the factory, Mercury’s 16-amp stator and flywheel systems used ferrite-based magnets , often referred to generically as ceramic magnets. These magnets were embedded in either a cast steel flywheel or, in the case of factory racing flywheels, a lightweight aluminum version. While ferrite magnets are relatively corrosion-resistant and cost-effective, they are also brittle , prone to chipping or cracking, especially under the extreme vibrations and thermal cycling typical of high-performance outboard use. Their magnetic output is stable but relatively modest, matching the voltage handling characteristics of the early rectifiers and ignition modules used in these systems. Modern billet aluminum flywheels used in performance upgrades often replace the original ferrite magnets with rare-earth magnets , such as neodymium. These magnets can produce up to three times the magnetic field strength  of the originals. That increased field density translates directly into higher stator output voltage —a benefit in theory, but one that quickly becomes a liability when used with the unregulated three-post rectifiers  that Mercury originally supplied with many of these engines. In a standard 16-amp system, the stator output at idle might be around 30 volts AC. But at high RPM—especially in the 7,200+ range common with the 260 EFI, Drag, and S3000 platforms—AC voltage can climb beyond 90 volts. When rectified but left unregulated, this can produce DC charging voltages as high as 15.5 to 17 volts , depending on the battery’s load and condition. Such levels far exceed what most 12V batteries or electronic systems can tolerate. Overvoltage at this scale has a direct and measurable impact on engine reliability . Batteries begin to gas and boil, especially if they are sealed AGM types, and over time, cells will dry out and fail. Lithium batteries without a proper Battery Management System (BMS) can enter protection mode or shut down altogether. Deep cycle batteries, though often marketed as "marine-grade," are generally not well-suited for the fast-charge, high-RPM environment of a 2-stroke outboard stator system. A large, flooded lead-acid starting battery remains the most tolerant  of brief overvoltage conditions due to its internal structure and buffering capacity. But it’s not just the battery at risk. Mercury’s ADI and CDI ignition systems —especially the switchboxes and stator windings—are highly sensitive to excessive voltage. Consistent exposure to anything above 15 volts DC  can cause switchbox overheating, misfires, and eventually catastrophic failure. If voltages in the 16–17V range are observed during operation, the engine should be shut down immediately  to prevent ignition or charging system damage. To resolve this, a combined 20-amp regulator/rectifier  is the proven solution. This modern unit performs both rectification and voltage regulation, clamping output safely at approximately 14.4 volts , regardless of engine speed or stator voltage input. This makes it ideal for use with rare-earth magnet billet flywheels and high-RPM applications. It ensures consistent, safe battery charging and stable voltage delivery to all engine electronics. The 20-amp regulator/rectifier also offers a direct replacement for a long list of Mercury’s original unregulated rectifier part numbers, including 154-6770, 18-5707, 49184, 62351A1, 62351A2, 70350A1, 70350A3, 72310, 8M0058226, 816770, 816770T, and 9-17100 . Additionally, it replaces Mercury’s older two-wire voltage regulator , part number 88825-A7 , used on many 2.4L and 2.5L race engine blocks. To facilitate installation, a billet aluminum mounting bracket  is available, designed to bolt directly to the top of the V6 powerhead using factory mounting bosses, maintaining a clean, vibration-resistant, and heat-dissipating install location. For owners and builders of Mercury 2.0L, 2.4L, and 2.5L high-performance outboards—especially those running billet flywheels and pushing well above 7,000 RPM—the voltage regulation system must match the increased stator output. The original rectifiers were never designed for this much magnetic energy. Replacing the three-post rectifier with a properly regulated 20-amp unit, and using a compatible bracket that mounts cleanly in place of the original 88825-A7 regulator, is the correct, reliable, and proven approach  to modernizing the charging system for these legacy two-stroke powerhouses.

Monitor and tune your Mercury 2-stroke V6 outboard with precision using the Koso EGT-02R EVO. Learn how to operate the dual EGT and RPM gauge for real-time performance insights, data logging, and engine protection. This guide explains how to operate and fully utilize the Koso EGT-02R EVO digital gauge, focusing on its EGT, RPM, voltage monitoring, recording, playback, and customization features. Designed for high-performance applications, this system is particularly useful for Mercury 2.0L, 2.4L, and 2.5L V6 outboard engines used in racing, tuning, and diagnostics. 1. Understanding the Display and Basic Navigation When powered on, the Koso gauge enters the main screen , which continuously displays real-time engine data. Left Side : Displays EGT Left (port bank), or Max EGT Left when toggled. Right Side : Displays EGT Right (starboard bank), or system voltage when toggled. Bottom Center : Displays current engine RPM, sourced either from a signal wire or inductive pickup. Navigating the Display: Press the Left button  once to switch between live EGT Left and Max EGT Left. Press the Right button  once to switch between live EGT Right and voltage display. Hold the Left button for 3 seconds  while viewing Max EGT Left to clear that value. Hold the Right button for 3 seconds  on the main screen to toggle temperature units between Celsius and Fahrenheit. This intuitive layout allows you to monitor your engine’s thermal behavior and electrical system without diving into submenus. 2. Setting Warning Thresholds and Preferences The gauge allows you to configure alerts for key metrics like EGT and voltage. These warnings are critical for catching lean conditions, detonation, or charging system failures. Entering Settings Mode: Hold both buttons for 3 seconds  from the main screen to enter the settings menu. Once inside the settings screen: Press the Left button  to cycle through setting options: EGT L Warning Temperature EGT R Warning Temperature Low Voltage Warning High Voltage Warning Auto Record Delay Backlight Brightness Press the Right button  to adjust the value of the selected setting. The value will blink to indicate it is being edited. Notes: EGT warning range: 200–1000°C (or 392–1832°F), adjustable in 1° increments. Voltage warnings: Low = 8.0–13.0V, High = 13.0–16.0V, adjustable in 0.1V increments. Backlight brightness: Adjustable from 1 (dim) to 5 (bright). Auto record delay: 0–60 seconds. If no input is detected for 20 seconds, the system will automatically exit back to the main display. 3. Recording Engine Runs Recording is one of the most powerful tools in the EGT-02R EVO. It allows you to log and analyze thermal behavior and engine response over time, such as during acceleration tests or full-throttle passes. To Begin Recording: From the main screen , press both buttons together  to enter the recording mode. Press the Left button  once to begin recording. The “REC” icon will appear and begin blinking. To stop the recording, press the Left button again . The data is now stored. You can record up to 50 sessions , each lasting up to 99 minutes and 59 seconds . 4. Clearing Recorded Data If you need to wipe all previous logs: While in the recording screen, hold the Left button for 3 seconds . The gauge will enter a confirmation screen. Wait a few seconds to complete the data clearing or press either button for 3 seconds to cancel. 5. Playback Mode Playback is especially useful for reviewing engine behavior after test runs or races. It allows you to rewatch EGT and RPM fluctuations and assess the effectiveness of tuning adjustments. To Enter Playback Mode: From the recording screen , press both buttons again  to enter playback. Use the Left button  to select the run you want to view. Use the Right button  to control playback speed. Options include: 1x (real-time playback) 3x (fast-forward) 1/3x (slow motion) Rewind To exit playback and return to the main screen, hold the Right button for 3 seconds . 6. Viewing and Clearing Max EGT Values During operation, the gauge automatically stores the highest recorded EGT for both channels. This is helpful for post-run analysis or spotting potential over-temp conditions that occurred too fast to catch live. To View Max EGT: Press the Left button  from the main screen to switch from live EGT L to Max EGT L. Press the Right button  to view Max EGT R. To Clear Max EGT: While viewing a Max screen, hold the Left button for 3 seconds  to reset the value. This does not affect your recorded sessions—just the live memory of peak values since the last clear. 7. Using the Temperature Unit Toggle The gauge supports both Celsius and Fahrenheit. To change the display unit: Hold the Right button for 3 seconds  from the main screen. The temperature values will switch units accordingly. This toggle is instant and can be done at any time—no need to enter the settings menu. 8. Adjusting Backlight Brightness To adapt the display to sunlight, shade, or night conditions, you can adjust the backlight brightness. Enter the settings menu by holding both buttons for 3 seconds . Scroll to the backlight option using the Left button. Use the Right button to choose a level between 1 (dark)  and 5 (bright) . This setting is stored until manually changed, ensuring consistency between sessions. 9. Visual Warnings and Alerts The gauge will alert you with flashing values if any monitored variable exceeds your preset threshold: If EGT Left or Right exceeds its configured limit, the temperature will blink. If voltage rises above or drops below its set limits, the voltage readout will flash. These visual warnings are essential for real-time awareness during operation, especially under high load or prolonged throttle. 10. Practical Tips for Use Always check Max EGT after a full-throttle pass. High temps can indicate lean conditions or timing issues. Use the data logging feature to compare before-and-after results when making tuning changes (e.g., jetting, ignition). Set voltage alerts conservatively if you're using older batteries or race-specific electrical systems. Toggle between °F and °C depending on your familiarity or team standard. The Koso EGT-02R EVO is not just a readout—it’s a performance tuning and engine protection tool. By understanding and leveraging its features, you can gain deep insights into your engine’s thermal behavior, identify hidden issues before they become expensive failures, and extract maximum performance under safe conditions. Whether you're logging data after every race lap or monitoring for safe cruising, this gauge offers real-time, accurate feedback that supports confident tuning and operation. Koso EGT-02R EVO Dash Manual - Free Download PDF User Guide

044 Style EFI Pump Flow Estimates at Varying Voltage & Pressures The Buckshot Racing #77 EFI fuel pump, a high-performance Bosch 044-style replacement, is widely trusted for demanding EFI applications in marine and motorsport environments. The spec flow rates for the pump are 79 GPH (300 LPH)  at 43 PSI and 13.5 volts , 67 GPH (255 LPH)  at 43 PSI and 12 volts , and 53 GPH (200 LPH)  at 75 PSI and 12 volts . These values reflect real-world performance across different voltage conditions. Since electrical system voltage varies depending on battery chemistry—lead-acid batteries average 12.4–12.6V, AGM batteries around 12.7V , and lithium iron phosphate (LiFePO4) batteries often sit between 13.0–13.4V —this evaluation assumes a practical baseline of 12.7 volts  to reflect common high performance use. At 12.7V and 43 PSI, the 044-style pump is estimated to flow approximately 71 GPH (270 LPH) . Like all electric fuel pumps, its flow rate decreases as pressure increases, typically by 10–15% per 10 PSI . Understanding this pressure-flow relationship is essential for designing fuel systems for Mercury 2.5L EFI engines, which vary in both fuel pressure and volume depending on model and modification level. Below are a few examples. The Mercury Marine Laser or XRi  type front injected motor requires approximately ~ 26 GPH (98 LPH)  at 33 PSI  at wide-open throttle (WOT). At this relatively low pressure, the Buckshot #77 pump outputs over 74 GPH (280+ LPH) , offering nearly 3× the required flow , ensuring excellent injector supply and pressure stability under load. The Mercury Racing 260 EFI  demands slightly more fuel at WOT, requiring ~ 28 GPH (106 LPH)  at 39 PSI . At this pressure, the pump continues to deliver around 70–71 GPH (265–270 LPH)  at 12.7V, again offering a safe 2.5× flow margin , suitable for high-performance recreational and competition use. The Mercury Race 280 ROS, 300 Drag, and S3000  versions require a higher flow of ~ 30 GPH (114 LPH)  at 56 PSI , pushing the system closer to the high-pressure limit of the pump. At this pressure, flow output is estimated at 58–61 GPH (220–230 LPH) . The pump provides roughly 2× the required fuel volume , ensuring consistent WOT operation with solid headroom. For heavily modified Mercury 2.5L engines  producing 350+ horsepower , estimated fuel demand rises to ~ 35 GPH (132 LPH)  at approximately 56 PSI , depending on porting, RPM range, and final tune. In this case, the 044-style pump, delivering ~ 60 GPH (220–230 LPH) , offers around 70–75% flow overhead , which is generally acceptable for high-output naturally aspirated builds. For ultra-high-performance, a ~110 GPH (400LPH+) pump setup may be more suitable to maintain safe injector pressure and flow margin. In conclusion, the Buckshot Racing #77 EFI pump provides robust flow performance across a wide range of pressure and voltage conditions. With a real-world baseline output of 71 GPH (270 LPH)  at 12.7V and 43 PSI, it is fully capable of supporting all Mercury 2.5L EFI variants—whether it's a stock Laser XRi, a tuned 260 ROS, a high-pressure 300 Drag, and would support fully built 350+ HP motor with the 1/2" input, no bends and no 90 degree fittings are recommended. We would soft bends on your fuel hose to reduce flow distribution including airation in the lines that can be caused by hard bends. With proper voltage management, high flow filtrs, and return-style fuel regulation, this pump delivers consistent performance and headroom even under wide-open throttle and race conditions.

Johnson and Evinrude Rotary Outboards: OMC's Daring Leap into Wankel Rotary Power OMC’s Vision for Rotary Innovation In the early 1970s, Outboard Marine Corporation (OMC)—the parent of the Johnson and Evinrude brands—embarked on a bold mission to redefine marine propulsion. Their inspiration came from the groundbreaking work of German engineer Felix Wankel, who invented the rotary combustion engine (known as the Wankel engine) in the 1950s. Unlike traditional piston engines, the Wankel design offered smoother operation, higher RPM potential, compact size, and fewer moving parts—all advantages that aligned perfectly with the needs of high-performance outboard motors. OMC first applied rotary technology in 1972 by introducing a Wankel rotary engine into snowmobiles. The engine's lightweight construction, simplicity, and remarkable power-to-weight ratio impressed engineers and corporate leadership alike. Seeing its success on land, OMC’s next ambitious step was to bring this innovation to the water, believing that a rotary-powered outboard could outperform anything Mercury Marine had in their arsenal. The result was a series of Johnson rotary outboards and Evinrude rotary outboards featuring single-rotor, twin-rotor, and even an experimental four-rotor design engineered for racing at the highest competitive levels. OMC believed these engines could offer smoother throttle response, lighter weight, and superior top-end speeds, setting new standards for marine propulsion. Racing Debut and Triumphs By 1973, the Johnson and Evinrude rotary outboards were ready to face their fiercest competition—Mercury Racing and Mercury High Performance. OMC fielded these revolutionary engines in tunnel boat races on both sides of the Atlantic, powered by some of the biggest names in the sport, including Jimbo McConnell and Johnnie Sanders. The rotary outboards demonstrated blistering acceleration, smoother throttle response, and competitive top-end speed that challenged Mercury’s long-standing dominance. The racing community’s reaction was electric. Many marveled at OMC’s technological leap forward, while Mercury Racing crews quickly recognized the serious challenge Johnson and Evinrude posed. For a brief but thrilling period, Johnson and Evinrude vs Mercury Hmatchups became headline events, symbolizing one of the most intense rivalries in outboard racing history. 🥇 1973 Windermere Grand Prix (United Kingdom) OMC’s first major international success came at the 1973 Windermere Grand Prix in England. Johnson and Evinrude rotary-powered boats outpaced the competition on the narrow and technical course, showcasing the rotary engine's smoothness and agility. This victory proved that rotary power could dominate in real-world race conditions, even against Mercury High Performance equipment. 🏆 1973 Galveston Speed Classic (United States) Later that year, OMC’s rotary boats swept the Galveston Speed Classic in Texas. Johnson and Evinrude entries finished 1st, 2nd, and 3rd, while a fourth rotary-powered boat had been leading before crashing out. The Galveston sweep sent shockwaves through the racing world, showing that OMC's new technology was not just competitive—it was dominant. 🚤 1974–1975 U.S. Tunnel Boat Championships Throughout the 1974 and 1975 tunnel boat racing seasons, rotary-powered Johnson and Evinrude boats continued to make headlines. Drivers like McConnell and Sanders often secured pole positions and led laps against Mercury Racing’s best. Although endurance issues occasionally forced retirements, the sheer speed of the rotary engines repeatedly pushed Mercury Hi-Perf engineers to rethink and improve their racing programs. OMC’s rotary engines had changed the game—but keeping up the momentum proved difficult. Strengths and Setbacks Although the OMC rotary outboards proved incredibly competitive, several critical hurdles emerged. Manufacturing costs were extremely high due to the complex nature of the Wankel rotary engine. Maintenance was more complicated than the rugged, simple designs Mercury High Performance engines relied on. Furthermore, tightening environmental regulations made the fuel economy and emissions of the rotary engine less favorable compared to Mercury's traditional two-stroke powerplants. Despite their superior speed and innovation, the Johnson and Evinrude rotary outboards struggled to find a path to commercial viability. Enthusiasm from racers and engineers could not overcome the practical challenges facing production and widespread adoption. The End of the Rotary Dream By the late 1970s, OMC officially ended the rotary outboard project. Without the ability to mass-produce economically or satisfy environmental standards, the rotary Johnson and Evinrude engines were shelved. Mercury solidified their dominance in the performance and racing markets, while OMC retreated to focus on more traditional two-stroke designs. Nonetheless, the impact of the Johnson and Evinrude rotary outboards remains significant. Their brief but brilliant presence pushed technological boundaries, forced Mercury Racing to innovate, and left an enduring legacy of daring engineering that marine historians and collectors still celebrate today.

Hydraulic Steering Self-Bleeding Kit from Buckshot Racing 77 Instructions for SeaStar and Like-Kind Steering Systems The Hydraulic Steering Self-Bleeding Kit from Buckshot Racing 77  is designed for bleeding SeaStar  and like-kind front-cylinder hydraulic steering systems (such as Pro Steering, and UFlex). This bleed kit system enables single-operator bleeding  without the use of pressure-fill equipment, helping to reduce the risk of seal damage at the helm or cylinder. Kit Components Brass steering helm adapter fitting Steering cylinder bridge tube Fill tube Fluid bottle connector with snap-fit to helm adapter Instructions for Use 1. System Preparation Inspect all steering system components, including hoses and fittings, for wear or damage. Center the outboard motor or rudder. Secure the vessel to prevent movement during the bleeding process. 2. Connecting the Bleed Kit Attach the bridge tube  to both bleed fittings  on the steering cylinder. This creates a closed loop that allows fluid to circulate through both sides of the cylinder. Remove the fill plug from the helm pump. Install the brass helm adapter  into the fill port and connect the fill tube . Attach the fluid bottle connector  to a container of approved hydraulic steering fluid. Position the bottle above the helm  for gravity feed. 3. Bleeding Procedure Turn the steering wheel fully clockwise . This allows fluid to move through the system, displacing air into the bridge tube. Turn the wheel fully counterclockwise  to reverse the fluid flow. Repeat this cycling process several times. Monitor the bridge tube for air bubbles . Continue until no bubbles are visible. Maintain the fluid bottle at an elevated level throughout the process to ensure consistent fluid feed and to prevent air from re-entering the helm. 4. Final Steps and System Check Close both bleed fittings once the system is confirmed free of air. Disconnect the bridge tube and fill tube. Reinstall the helm’s fill plug and tighten securely. Turn the wheel fully in both directions to confirm proper system function. Inspect all connections for leaks. Additional Notes The Hydraulic Steering Self-Bleeding Kit from Buckshot Racing 77 is compatible with SeaStar and other front-cylinder hydraulic systems. It supports a range of high-output systems, including Buckshot Racing 77 350 HP and 700 HP steering setups. This kit is intended for use with gravity feed only. External pressurization is not recommended. Download PDF Instructions free: Sheet Hydraulic Steering Self-Bleeding Kit:

Iron Fist: The Lives of Carl Kiekhaefer  by Jeffrey L. Rodengen tells the story of Carl Kiekhaefer, the visionary founder of Mercury Marine. His relentless drive transformed a failing outboard company into a global leader, revolutionizing marine propulsion and high-performance engineering. Known as "The Iron Fist," Kiekhaefer demanded excellence and perfection, often at great personal and professional cost. Through innovation and obsession with racing, Kiekhaefer advanced outboard technology, creating durable, lightweight engines that set industry standards. His passion for competition helped Mercury dominate racing circuits, cementing its reputation for performance. Beyond marine applications, his engineering brilliance extended to military and industrial fields, showcasing his versatility. Kiekhaefer’s life offers lessons on leadership, vision, and the price of perfection. Despite his challenges, his legacy remains a blueprint for pushing limits and achieving greatness. Here are the top 10 facts we can learn about Carl Kiekhaefer from the book: 1. Obsessive Perfectionism Carl Kiekhaefer was known for his relentless pursuit of perfection. He believed in building products that were not just good but flawless. This obsession extended to every aspect of his work, from product design to employee performance. 2. Transformative Vision for Outboards Kiekhaefer took over a failing outboard motor business in 1939 and turned it into one of the most innovative and successful marine companies in the world. He envisioned outboards not as basic utility motors but as powerful, reliable tools for performance and recreation. 3. Ruthless Leadership Style Kiekhaefer's leadership style earned him the nickname "The Iron Fist." He demanded loyalty, perfection, and absolute dedication from his employees. While this approach yielded exceptional results, it also created an intense and sometimes controversial work environment. 4. Mercury’s Dominance in Racing Under Kiekhaefer’s leadership, Mercury became synonymous with high-performance marine engines. His personal involvement in racing helped Mercury outboards dominate powerboat racing circuits, solidifying the brand’s reputation for speed and reliability. 5. Expansion Beyond Marine Engines Kiekhaefer's engineering brilliance extended beyond marine engines. Mercury Marine produced engines for military vehicles, chainsaws, and even air-cooled engines for various industrial applications during its early years. 6. Work Ethic Defined His Life Kiekhaefer was known for working incredibly long hours, often sleeping on-site to oversee production. His commitment to his company and products was unparalleled, and he expected the same from those around him. 7. Revolutionary Marketing Tactics Kiekhaefer pioneered unique marketing strategies that focused on reliability and performance. He famously subjected Mercury engines to grueling endurance tests, like running them 50,000 miles non-stop, to showcase their durability. 8. Emphasis on Engineering Innovation The book highlights Kiekhaefer’s engineering genius. He constantly pushed his team to develop groundbreaking technologies, including lightweight materials, better cooling systems, and improved fuel efficiency for outboards. 9. Difficult Personal Relationships Kiekhaefer's intensity and single-mindedness often strained his relationships. His demanding personality made it difficult for colleagues and even family members to connect with him on a personal level. 10. Legacy of Excellence Despite his controversial leadership style, Kiekhaefer’s dedication to innovation transformed the marine industry. His focus on reliability and performance continues to influence Mercury Marine’s ethos today, ensuring that his legacy endures. Carl Kiekhaefer’s story, as told in Iron Fist , reveals a complex, driven individual whose passion and brilliance changed an industry forever. The book serves as both an inspiring tale of achievement and a cautionary study of leadership under intense pressure.

SeaStar Solutions offers a comprehensive range of hydraulic steering systems tailored for various boating and marine applications, each comprising specific components with unique part numbers. We provide this as a reference for those who are upgrading to our complete 350 HP Hydraulic Steering Systems, 700 HP Hydraulic Steering Systems, custom length steering hose lines, our faster 2.7 Helm, or 700 HP Front Cylinder or use our Self-Bleeding Kit (for one-person operation). Most all our steering parts are compatible and interchanging with Sea Star to ensure that we can cost-effectively solve our customer rigging needs. Below is an organized overview of key boat hydraulic steering parts and their associated part numbers: 1. Hydraulic Helm Pumps Capilano Series – Inboard Steering Helms SeaStar Capilano Helm 1250V (HH5250) Rear Mount, Variable Displacement: 1.7–3.4 cu. in.  – Ideal for small to mid-size inboard boats. SeaStar Capilano Helm 1275V (HH5275) Rear Mount, Variable Displacement: 2.7–5.4 cu. in.  – Best suited for larger inboard vessels requiring increased steering output. SeaStar Standard Outboard Helms HH5271-3  – 1.7 cu. in. Front Mount Helm HH5273-3  – 2.0 cu. in. Front Mount Helm HH5272-3  – 2.4 cu. in. Front Mount Helm HH5261-3  – 1.7 cu. in. Rear Mount Helm HH5262-3  – 2.4 cu. in. Rear Mount Helm HH5291-3  – 1.7 cu. in. Sport Tilt Helm HH5292-3  – 2.4 cu. in. Sport Tilt Helm HH5741-3  – 1.7 cu. in. Classic Tilt Helm HH5742-3  – 2.4 cu. in. Classic Tilt Helm SeaStar Pro Series – High-Performance Helms Perfect for high-speed outboard applications (60+ MPH) HH5779-3  – 1.7 cu. in. Standard Mount HH5778-3  – 1.7 cu. in. Rear Mount HH5773-3  – 1.7 cu. in. Tilt Helm HH5770-3  – 2.0 cu. in. Standard Mount HH5771-3  – 2.0 cu. in. Rear Mount HH5774-3  – 2.0 cu. in. Tilt Helm HH5290-3  – 2.0 cu. in. Sport Tilt HH5772-3  – 2.4 cu. in. Standard Mount 2. Hydraulic Steering Cylinders Outboard Front Mount Steering Cylinders Models : HC5340-3, HC5342-3, HC5345-3, HC5347-3, HC5348-3, HC5358-3 Other Mount Types Side Mount Cylinder : HC5370-3 Splashwell Mount Cylinder : HC5380 Catamaran/Pontoon Cylinder : HC5375-3 Inboard Steering Cylinders Models : HC5312-3, HC5313-3, HC5314-3, HC5318, HC5319 3. SeaStar Hydraulic Hose Kits Standard Hydraulic Hose Kit (2 hoses) : HO51xx Bulkhead Hose Kit (2 hoses) : HO81xx Note: 'xx' refers to length in feet (e.g., HO5108 = 8 ft hoses). 4. Hydraulic Fitting Kits Add-A-Station Kit (Nylon/Copper) : HF6010 Add-A-Station Kit (Hose) : HF6007 Autopilot Fitting Kit (All Helms) : HF5502 5. Steering Tubing 3/8” Diameter Nylon Tubing : HT5xxx Available in custom lengths, perfect for low-pressure return lines. 6. Hydraulic Steering Fluid SeaStar Hydraulic Oil – 1 Quart : HA5430 SeaStar Hydraulic Oil – 1 Gallon : HA5440 Recommended fluid for all SeaStar hydraulic systems for maximum performance. 7. Steering Service Parts Helm Shaft Seal & Locknut Kit : HP6032 Steering Wheel Hardware Kit : SA27454P 8. Optional Accessories Round Bezel Kit : HA5478 Backplate Kit : HA5418 20° Dash Wedge Kit : HA5419 Power Assist Steering Unit : PA1200-2 Provides effortless control and better handling in high-torque conditions. *Note: The 'xx' in part numbers (e.g., HO51xx) denotes variable lengths or specific configurations. It's essential to select the appropriate specifications based on your boat's requirements. By utilizing the correct part numbers, you can ensure compatibility and optimal performance of your SeaStar steering system.

Thinner cylinder head gaskets can increase compression in an engine by reducing the volume of the combustion chamber. In a 2-stroke outboard engine like the Mercury 2.0, 2.4, and 2.5 Liter V6 Outboard, the head gasket sits between the cylinder head and the engine block, sealing the combustion chamber. When you replace the stock head gasket with a thinner one, you effectively decrease the space between the cylinder head and the engine block. This reduction in thickness reduces the volume of the combustion chamber when the piston is at Top Dead Center (TDC), which increases the compression ratio. Increasing the compression ratio may improve engine performance by boosting power output and torque. Nevertheless, it is important to consider that adjusting the compression ratio can impact engine reliability, fuel octane demands, and the risk of detonation (pre-ignition) if not handled correctly. It is crucial to consult with experienced mechanics or engine tuners before making any modifications to the head gasket or compression ratio of your Mercury V6 outboard. They understand the specific requirements and potential risks associated with such modifications. But, here are a few examples of available Mercury 2.5 Liter Cylinder Head Gasket by thickness: Head Gasket Thickness & Suggested Clearance 0.75mm (0.0295" thickness) is suggested for pistons at .008" (or more) below deck height 1.00mm (0.0393" thickness) is suggested for pistons at .000" (or more) below deck height 1.10mm (0.0433" thickness) is suggested for pistons at .004" (or less) over deck height 1.20mm (0.0472" thickness) is suggested for pistons at .008" (or less) over deck height 1.50MM (0.0591" thickness) is suggested for pistons at .020" (or less) over deck height Sometimes, in cases where the 2.5 block is damaged and requires deeper decking than usual to achieve a flat and even surface, a thicker 1.5mm gasket may be necessary. This additional clearance is essential to prevent the piston from protruding excessively from the deck and potentially coming into contact with the head.  In a Mercury 2.5L V6 2-stroke at zero deck and a 3.500" bore, head gasket thickness directly affects compression by altering combustion chamber volume. A thin 0.0295" (0.75 mm) gasket adds just 4.65 cc, while a 0.0393" (1.00 mm) gasket contributes 6.20 cc. Thicker options like 0.0433" (1.10 mm), 0.0472" (1.20 mm), and 0.0512" (1.30 mm) increase volume to 6.82 cc, 7.44 cc, and 8.06 cc, respectively. The thickest commonly used, at 0.0591" (1.50 mm), adds 9.32 cc. Thinner gaskets raise compression and improve combustion efficiency, while thicker ones reduce compression and are often used for detonation control or when pistons protrude slightly above the deck.

Optimize your Mercury 2.5 Liter 2-Stroke V6 Outboard with the proper interdependencies of Deck Height, Squish Clearance, and Cylinder Head Gasket Thickness! Building or upgrading Mercury 2.5 Liter 2-Stroke V6 outboards for high performance requires precise management of three critical parameters: deck height , squish clearance , and cylinder head gasket thickness . These factors are intricately linked, and their proper calibration is essential for maximizing power, efficiency, and reliability. The right selection of cylinder head gaskets plays a pivotal role in tuning these engines for optimal performance. Deck Height Deck height , the distance between the piston top and the cylinder block deck at Top Dead Center (TDC), directly impacts the engine’s compression ratio and port timing. Lowering the deck height increases compression, enhancing power and efficiency, but also raises the risk of detonation or pre-ignition if not handled carefully. Machining the deck to achieve the correct height ensures compatibility with squish clearance and gasket thickness, which are equally critical to performance. Squish Squish clearance , the gap between the piston top and the cylinder head’s squish band at TDC, promotes turbulence in the combustion chamber. This turbulence improves combustion efficiency, ensuring that the air-fuel mixture burns evenly and quickly. Proper squish clearance reduces detonation risk and boosts power output. For high-performance Mercury outboards, squish clearance typically ranges from 0.035" (very aggressive) to 0.040" (safe & dependable HP) to 0.060" (low octane safe, loss of HP) , depending on the engine’s RPM range and intended use. Measuring and fine-tuning squish clearance during a mock assembly is crucial for achieving the desired performance. Gasket Thickness The cylinder head gasket  is a key component for sealing the combustion chamber and fine-tuning both compression ratio and squish clearance. Buckshot Racing #77 provides updated gasket thickness recommendations tailored to the specific deck height and piston positions of Mercury 2.5L V6 outboards: 0.75mm (0.0295") : This is a specialty gasket  designed for Nikasil blocks  and race applications. It is recommended for pistons at 0.008" (or more) below deck height , ensuring tight squish clearance and enhanced combustion efficiency in high-performance setups. Racer who have explored the limits may be able to run tighter squish tighter squish clearances. 1.00mm (0.0393") : This is also a specialty gasket  designed for high performance applications. Ideal for pistons at 0.000" (or more) below deck height , balancing compression and safety for performance-focused builds. Racer who have explored the limits may be able to run tighter squish clearances. 1.10mm (0.0433") : Suggested for pistons at 0.004" (or less) over deck height , providing a safe and effective squish clearance for high-performance applications. Racer who have explored the limits may be able to run tighter squish clearances. 1.20mm (0.0472") : Best for pistons at 0.008" (or less) over deck height , ensuring reliability and optimal compression in high-performance and recreational setups. Racer who have explored the limits may be able to run tighter squish clearances. 1.50mm (0.0591") : This is a specialty gasket  designed for decked blocks found in remans, re-sleeved blocks, and highly modified blocks where tuners are raising port timing by decking the block , making it ideal for aggressive performance builds or rebuilders trying to save a block that has been over-deck through the years with pistons at 0.020" (or less) over deck height . Racer who have explored the limits may be able to run tighter squish clearances. Selecting the correct gasket thickness is crucial for tuning compression and squish clearance to align with the engine’s configuration. For example, a thinner gasket like the 0.75mm  increases compression and is best suited for Nikasil and race applications where every fraction of performance matters. Conversely, a thicker gasket like the 1.50mm  is essential for specialty builds, such as decked or re-sleeved blocks, where raising port timing is necessary to achieve performance goals. Both gaskets cater to specific, high-demand applications. The interplay between deck height, squish clearance, and gasket thickness is the foundation of a high-performance build. Adjusting one parameter influences the others, necessitating a holistic approach. For instance, reducing deck height tightens squish clearance, requiring a reassessment of gasket thickness to maintain safe operating conditions. Likewise, increasing gasket thickness may preserve squish clearance but alter compression, affecting the engine’s overall performance. Precision measurement is essential to successful engine assembly. Tools like micrometers, bore gauges, and feeler gauges should be used to confirm tolerances during mock assembly. Afterward, thorough testing under operating conditions ensures that all adjustments function harmoniously. Using high-quality components, such as Buckshot Racing #77’s head gaskets, ensures durability and consistency across performance applications. Whether your goal is to build a racing powerhouse or a durable recreational engine, careful management of deck height, squish clearance, and cylinder head gasket thickness is vital. Buckshot Racing #77 offers the widest available range of gasket thicknesses specifically designed for Mercury 2.5L V6 outboards, tailored to meet the needs of any build. By following these updated recommendations and selecting the appropriate specialty gasket for your application, you can achieve peak performance, improved combustion efficiency, and enhanced reliability for your high-performance Mercury outboard. Note: In a Mercury 2.5L V6 2-stroke at zero deck and a 3.500" bore, head gasket thickness directly affects compression by altering combustion chamber volume. A thin 0.0295" (0.75 mm) gasket adds just 4.65 cc, while a 0.0393" (1.00 mm) gasket contributes 6.20 cc. Thicker options like 0.0433" (1.10 mm), 0.0472" (1.20 mm), and 0.0512" (1.30 mm) increase volume to 6.82 cc, 7.44 cc, and 8.06 cc, respectively. The thickest commonly used, at 0.0591" (1.50 mm), adds 9.32 cc. Thinner gaskets raise compression and improve combustion efficiency, while thicker ones reduce compression and are often used for detonation control or when pistons protrude slightly above the deck.

Mercury 2-stroke ignition modules: spark advance, detonation control, and idle speed control for 2.0L, 2.4L, 2.5L outboards This technical guide outlines the basic function, application, and service considerations for key ignition-related modules used in Mercury 2-stroke outboard engines , including both EFI  and carbureted models . Specifically, it focuses on 1) the spark advance module  ( 93772A1  and variants), 2) detonation control module  ( 825164  and 14856A3 ), and 3) the idle speed control module  ( 87076A6  series). These components play critical roles in timing management , detonation prevention , and idle stability  across various engine families, including 2.0L , 2.4L , and select 2.5L V6  models. Understanding each module’s purpose and compatibility is essential for accurate diagnostics and maintaining optimal engine performance. The Mercury spark advance module   93772A1  is an ignition control component used in various 2-stroke Mercury outboard motors, specifically across the 2.0L  and 2.4L  engine families. Compatible part numbers include 93772A2 , 93772A3 , 93772A5 , 93772A7 , 93772A8 , and 93772A11 . This module was installed on models such as the Mercury XR2 , XR4 / Magnum II , XR6 , V-135 , V-150 , V-175 , and select early 2.5L V-200 EFI  engines. The module operates by altering bias voltage  to the switchbox, electronically advancing or retarding ignition timing depending on engine RPM . It advances timing below 600 RPM  to help stabilize idle and provides up to 6 degrees of advance  above 5000 RPM . Around 5700 RPM , the module retards timing by approximately 4 degrees  to reduce the risk of over-revving. This is the basis for the Buckshot Racing #77 custom race timing modules, both the Cherry Bomb and Plus 3 Boost Box. This module was commonly used on 2.4L carbureted  and EFI  engines, including the Bridgeport EFI , and in limited early applications of 2.5L EFI  models. Compatibility should always be confirmed using engine serial numbers  or official Mercury documentation . The 93772A1  and its related variants are no longer manufactured  and are known to degrade over time . Symptoms of failure include erratic idle , hesitation  during throttle response, or diminished top-end power . If diagnosed as faulty, the module can be removed and ignition timing manually adjusted  to factory specifications. Many engines from this era operate reliably without the module when properly timed. In contrast, the Mercury detonation control module —part numbers 825164  and 14856A3 —is designed to protect high-performance engines  from pre-ignition or knock . It functions by detecting detonation through cylinder vibration  and temporarily retards ignition timing to prevent engine damage. This module operates reactively , unlike the proactive  behavior of the spark advance module. The detonation control module is used in Mercury 2.5L EFI models  such as the 150 EFI Pro Max , 200 EFI Pro Max/Super Magnum , V-150 (MAG/EFI) , V-150XRI (EFI) , V-175 (SKI and MAG/EFI) , V-175XRI (EFI) , V-200 (MAG/EFI) , V-200XRI (EFI) , and the V-220 Laser (EFI) , typically producing between 150 and 220 horsepower . These engines use digital ECU systems  and aggressive timing curves. The detonation module is considered essential for engine protection  and should not be removed  unless replaced by a compatible ECU system . Another related component is the idle speed control module , part number 87076A6  and variants 87076A1 through 87076A9 . This module regulates idle speed  on EFI-equipped V6 engines  by interfacing with the ECU  and throttle position sensors . It maintains consistent idle under load changes—such as during gear shifts  or in rough water —by adjusting air and/or fuel delivery at low RPM. The idle speed control module was used in mid-to-late 1990s Mercury EFI outboards , including the 175 EFI , 200 EFI , and various Pro Max  models. A failing module may cause surging , inconsistent idle , or stalling . These modules are also discontinued . If diagnosed as defective, they typically require replacement . Removal is not recommended  unless replaced by a programmable or aftermarket ECU . In all cases, verifying part compatibility using engine serial numbers  and consulting official factory documentation  is essential. A full understanding of the function and integration of the spark advance , detonation control , and idle speed control modules  is critical for ensuring proper ignition timing , drivability , and performance  in Mercury 2-stroke outboard motors .