We offer a selection of 2.5-liter high-performance cylinder head gasket thicknesses that fit all 1991 - Present gasket-head Mercury Marine, Mercury Racing and Mariner 2.5 Liters including; XR6, XRi, 150 HP BB, 150 ProMax, 175HP CC, 200HP EE, 200HP FF, 225 Pro Max NN, 245HP KK, 260 ROS, LL, PP, SS blocks for all recreational sky, tournament bass fishing, outboard drag racing, and Seebold Sports USF1 & APBA F200 race 2-stroke powerheads to increase compression and performance.
 
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. Slightly thicker options like our 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.
 
We use Athena M0115 material on our 0.75MM and 1MM head gaskets and Victor Reinz AFM material on our 1.1MM, 1.2MM, 1,3MM, and 1.5MM head gaskets.
 
Athena M0115 is a high-performance gasket material manufactured in Italy, designed for demanding engine applications. It features an asbestos-free composite construction built around a pegged steel core, which adds structural strength and dimensional stability. 

Victor Reinz AFM is a premium German-engineered gasket material widely used in OEM automotive and marine applications. It is a fiber-reinforced elastomeric sheet composed of aramid fibers, mineral fillers, and rubber-based elastomers. 
 
2.5 Liter Head Gasket Thickness & Suggested Clearances
 
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
 
1.30mm (0.0512" thickness) for pistons at .011" or less over deck height (Mercury OEM)
 
1.50MM (0.0591" thickness) is suggested for pistons at .020" or less over deck height
 
Outboard boat racers who have explored the limits may be able to run tighter squish clearances.
 
Mercury OEM and other Part Numbers:
814658, 8146581, 18-3864, 184721, 35870, 822844, 822844T04, 822844T05, 822844004, 8228441, 8228442, 8228443, 9-63854, 814658-1 0.75, 822844-1 1.00, 27-840322-1 1.50
 
Includes one (1) Cylinder Head Gasket for your Mercury 2.5-liter Outboard.
 
Order the number of head gaskets needed and select your thickness before checkout, as the 2.5 V6 Merc powerhead requires two (2) gaskets if both heads are removed.
 
Contact Mike Hill at mike@buckshotracing77.com with technical questions