Thinnest metal head gasket for RB26?

[Chris Wilson]

What's the thinnest off the shelf quality multi layer shim head head gasket for an 87 mm (well, 86.5 actually) bore RB26 please? Thanks.

[wishaw]

correct me if i am wrong but wont that increase compression?

[NFAA32]

yes, smaller headgasket will inscrease cr, however, thinner gasket will reduce in strength,

correct me if im wrong(sydney kid), but wouldnt it be advisable, to shave the head, and use a thicker gasket for strength?

[Chris Wilson]

Head gasket "strength" does not, per se, come from thickness. The current trend to supply a trhicker gasket to reduce CR is just a lousy crutch to make this "easy". What it also does is increase the quench clearance, a bad thing. I can change < well, at least drop), CR by machining my piston tops, I need to reduce the quench clearance though, and this is more easiliy done by yusing a thinner head gasket than milling the block and having the pistons protrude more. hence the question re thinnest gasket. Thanks.

[pnblight]

i never seen anything under 1mm unfortunately

like the idea tho best of luck

[proengines]

Chris,

The thinnest we have found is a cometic gasket that comes out at very close to .040" compressed. It was 87.5mm bore size in the gasket. The last 26 we did we raised the compression slightly by milling the block until the piston protruded .010" out the top of the block. That gives .030" quench clearance between the quench pads on the piston and the head. I wouldn't go much less than this though, I'd say .025" clearance at a minimum depending on the RPM you're planning on using and the quality of rod/pin/piston. I think .030" is safe for 8500ish-9000RPM.

I saw in another post you mentioned you've seen the quench pads removed from the head. I've wondered about this too, we normally radius the edge of the pad and that's about it. I'd like to know what the benefit of removing the pad is, it would help by unshrouding the valves and would probably improve flame travel slightly but I'd say you would have to use a different profile on the piston dome to benefit from it. I'd say they must still leave a ring around the chamber to give quench.

I'd love to see someone with a lot more money than me make an aftermarket head with a flatter valve angle and smaller combustion chamber, something like an EJ20 or SR20 and use an almost flat top piston. I'd say the gains would be huge.

[netrati]

Apexi makes a 0.8mm headgasket for the rb26.