Upgrade your Mercury outboard engine with the Billet Race Relief Valve Cover Kit by Buckshot Racing #77, a high-performance replacement for factory-installed relief valve covers.
This part is precision CNC-machined from high-grade 6061 billet aluminum, then lightly glass bead blasted and anodized in your choice of red, blue, or black for an ultra-durable, corrosion-resistant finish that adds both function and visual appeal to your powerhead.
This billet cover is a direct replacement for Mercury Racing's 99193 Relief Valve Cover and Quicksilver's 687291, now sold under part number 8M0039767.
It fits a wide range of Mercury and Mariner 2-stroke V6 outboards (2.0L, 2.4L, 2.5L) produced from 1976 to 2015. That includes models such as the 135, 150, 175, and 200 horsepower engines, including well-known variants like the XR2, XR4, XR6, XRi, and Black Max.
It’s also the go-to upgrade for high-output engines like the 225 Pro Max, 245 Carb, 260 EFI, 280 ROS, and the iconic 300 Drag EFI. Additional compatibility includes SEAPRO, Marathon, SuperMagnum, and 300X EFI models—essentially covering most of Mercury’s most legendary V6 performance platforms.
Mercury Racing transitioned from the traditional spring-loaded poppet valve to a fixed relief-style valve cover on their race engines for one key reason: reliability.
In recreational motors, the poppet valve helps control cooling by opening under pressure, but in race conditions—where engines are operated at wide-open throttle for extended periods—these valves can flutter or fail, leading to inconsistent water flow or overheating.
The relief-style valve cover eliminates this issue entirely by removing moving parts and offering a fixed-flow outlet. This results in smoother water evacuation, consistent cooling, and reduced failure points, especially on modified or high-compression engines running high RPMs.
Each Billet Race Relief Valve Cover Kit includes one (1) anodized billet aluminum cover, two (2) stainless steel Allen head bolts, two (2) stainless lock washers, and one (1) premium cork gasket.
It’s a plug-and-play replacement for multiple OEM and aftermarket components and cross-references with part numbers such as 10-657, 18-0936, 31990, 508825, 540-28, 67624, 78690, 78690002, 9-60057, 18-0952, 32330, 88907, 88907003, 28782, and 27-889072.
Whether you're searching for a Mercury billet poppet cover, relief valve upgrade for 225 Pro Max, or a cooling system solution for a 260 EFI or 300 Drag, this cover from Buckshot Racing #77 delivers professional-grade durability and race-ready performance.
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.