Mercury Racing 2.5 Liter Hi-Performance Outboard Specifications (1994): 245 Carb, 260 EFI, 260 ROS
- Mike Hill
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- 2 days ago
- 5 min read
The 1994 Mercury Racing 2.5 Liter Hi-Performance ROS outboards are one of the most recognized Mercury V6 two-stroke platforms used in lake boats, race boats, offshore setups, restorations, rebuilds, and high-performance outboard projects.
Mercury Hi-Performance Service Bulletin No. 94-2 lists specifications for serial numbers 0D935000 through 0D936999, covering the Carb, EFI, and Offshore versions of the 2.5 Liter Hi-Performance outboard.
For Buckshot Racing #77 customers, this bulletin is a useful baseline when checking a used powerhead, identifying a real engine package, setting up ignition and fuel systems, comparing Carb versus EFI versions, or verifying service information during a rebuild.
Covered Mercury Racing 2.5 Liter Models
Mercury lists crankshaft horsepower at 265 HP for the Carb model and 280 HP for both the EFI and Offshore models. Propshaft horsepower is listed at 245 HP for the Carb model and 260 HP for both EFI and Offshore. Propshaft kilowatts are listed at 183 for Carb and 194 for EFI and Offshore.
This matters because many Mercury Racing engines are discussed by advertised or crankshaft horsepower, while propshaft horsepower is closer to what the drivetrain delivers to the water.
Displacement, Bore Type and Core Engine Specs
Mercury lists displacement at 153 CID, or 2530 cc. Bore is listed at 3.5 inches, or 88.9 mm, with a Nikasil bore type. Stroke is listed at 2.65 inches, or 67.3 mm.
These specs matter when ordering pistons, rings, bearings, gaskets, and other rebuild parts. Nikasil cylinders require the correct piston and ring package. They should not be treated the same as steel or cast-iron sleeved cylinders.
RPM, Timing and Compression
The bulletin lists idle speed at 675–750 RPM and maximum wide-open-throttle RPM at 7500 RPM. Idle timing is listed from TDC to +2°, and maximum spark advance is listed as 0.150 inch or 25° BTDC.
Compression ratio is listed at 6.25:1, with compression pressure listed at 130 psi, or 896 kPa.
These numbers are a factory reference point. A real-world engine may be different if it has cut heads, different gasket thickness, port work, sleeve repairs, piston changes, ECU changes, fuel system changes or modified ignition timing.
Fuel and Oil Requirements
Mercury lists the fuel recommendation as 92 minimum posted octane (R+M)/2, or 98 RON, unleaded. The bulletin also notes that premium unleaded gasoline is recommended for best performance and, when possible, fuel containing additives to clean fuel injectors should be used.
The oil recommendation is Quicksilver Performance Blend P/N 92-813743A-2, with the oil mixture listed at 32:1.
For performance use, fuel quality, correct octane, correct oil ratio and fresh fuel are not optional details. A high-performance Mercury Racing two-stroke should not be run hard on old fuel, unknown premix, low octane, or a questionable fuel supply.
Carb vs EFI Fuel Pressure
Fuel pressure is one of the biggest differences between the Carb and EFI versions. The Carb model is listed at 5 psi, or 34.5 kPa. EFI and Offshore models are listed at 38–40 psi, or 262–276 kPa.
This is a critical service point. A carbureted engine and an EFI engine do not use the same fuel pressure. Incorrect fuel pressure can cause hard starting, flooding, hesitation, lean running, poor idle, poor top-end performance or powerhead damage under load.
Ignition, Spark Plugs and Charging System
The firing order is listed as 1-2-3-4-5-6. Spark plug listings differ by model. The Carb model lists NGK BUHW, Mercury number 33-97180. EFI and Offshore models list NGK BUZHW, Mercury number 33-14103550.
Mercury lists the charging system as 16 amp, or 226 watt. Battery requirements are listed as a minimum reserve capacity of 100 minutes and minimum cold cranking capacity of 350 amps.
On EFI models especially, a weak battery, poor ground, dirty terminal, loose harness connection or charging issue can create problems that look like fuel or ECU trouble. Always verify the electrical system before replacing expensive parts.
Carburetor Jet Reference
For the Carb model, Mercury lists .072 break-in jets and .068 standard jets. EFI models are marked NA for these jet listings.
These factory jet numbers are a reference only. Jetting still needs to match the engine build, fuel, compression, timing, exhaust, altitude, temperature, load and use. Modified Mercury Racing engines may require different setup than the original bulletin baseline.
Lower Unit, Gear Ratio and Gear Lube
The bulletin lists lower unit capacity at 24 ounces and recommends Quicksilver Hi-Performance Gear Oil P/N 92-816026A-4.
On the continued specifications page, gear ratio is listed as 1.87:1, rotation is listed as Left & Right, flywheel is listed as Aluminum, and gear shift is listed as F-N-R.
These numbers are useful when identifying a lower unit, checking rotation, verifying gear ratio, servicing gear oil or ordering drivetrain parts.
Induction, ECU Box and Weight
The Carb version uses 3 carburetors. The EFI and Offshore versions use EFI induction. The ECU box is listed as N/A for Carb and P/N 11350A37 for EFI and Offshore.
Weight is listed at 350 lbs for Carb, 350 lbs for EFI and 375 lbs for Offshore.
That added Offshore weight can matter when comparing midsections, rigging, balance and race boat setup.
Transom Height Reference
Mercury lists transom height at 20 inches for Carb and EFI models. For Offshore, the bulletin lists Long = 20 inches and X-Long = 25 inches.
Because many Mercury Racing engines have been swapped, rebuilt, converted, re-rigged or assembled from mixed parts over the years, always verify the actual midsection, clamp bracket, gearcase and serial number instead of relying only on decals.
Quick Specification Summary
Specification | Carb | EFI | Offshore |
Crankshaft Horsepower | 265 | 280 | 280 |
Propshaft Horsepower | 245 | 260 | 260 |
Propshaft Kilowatts | 183 | 194 | 194 |
Displacement | 153 CID / 2530 cc | 153 CID / 2530 cc | 153 CID / 2530 cc |
Bore | 3.5 in / 88.9 mm | 3.5 in / 88.9 mm | 3.5 in / 88.9 mm |
Bore Type | Nikasil | Nikasil | Nikasil |
Stroke | 2.65 in / 67.3 mm | 2.65 in / 67.3 mm | 2.65 in / 67.3 mm |
Idle RPM | 675–750 | 675–750 | 675–750 |
Max WOT RPM | 7500 | 7500 | 7500 |
Max Spark Advance | 0.150 in / 25° BTDC | 0.150 in / 25° BTDC | 0.150 in / 25° BTDC |
Compression Pressure | 130 psi | 130 psi | 130 psi |
Fuel Octane | 92 AKI / 98 RON | 92 AKI / 98 RON | 92 AKI / 98 RON |
Oil Mix | 32:1 | 32:1 | 32:1 |
Fuel Pressure | 5 psi | 38–40 psi | 38–40 psi |
Firing Order | 1-2-3-4-5-6 | 1-2-3-4-5-6 | 1-2-3-4-5-6 |
Gear Ratio | 1.87:1 | 1.87:1 | 1.87:1 |
Rotation | Left & Right | Left & Right | Left & Right |
ECU Box | N/A | P/N 11350A37 | P/N 11350A37 |
Weight | 350 lbs | 350 lbs | 375 lbs |
Buckshot Racing #77 Tech Notes
The Mercury Racing 2.5 Liter Hi-Performance platform is a serious engine family, but the details matter. Carb, EFI and Offshore versions share the same basic displacement and core architecture, but they are not identical in fuel delivery, spark plug listing, ECU equipment, weight, fuel pressure or intended setup.
When inspecting, servicing or rebuilding one of these engines, check:
Serial number and model configuration
Carb, EFI or Offshore setup
Fuel pressure requirement
Fuel octane requirement
Oil mixture
Spark plug type
Compression pressure
Bore condition and cylinder material
Ignition timing
Battery and charging system health
Lower unit ratio and rotation
Gear oil type and capacity
Harness, grounds and ECU connections
These engines are now old enough that many have been rebuilt, ported, sleeved, re-ringed, converted, repaired or modified. Use the Mercury service bulletin as a starting point, then verify the engine in front of you.
Download: Mercury Service Bulletin and Tech Specs 245 Carb, 260 EFI, ROS >
Always enjoy reading and learning more about my 2.5