The V8 Owners Forum -

Ok that clears that up, the heads 36cc heads are more like 32cc that's where the missing 4cc have gone ,

What compression ratio do you think I would get if I used my 36(32)cc heads
My 22cc 9.35:1cr pistons with a composite gasket ?

I appreciate your comments that the inlet won't fit , and I understand why but could I get a bit milled off the inlet faces of both the heads or milled off the inlet manifold ?

I know I might not need to reduce it as" stevieturbo says"
I'm not running mega boost but it can't hurt and the composite ones do seal better

If you lower the compression ratio by using thicker head gaskets, the clearance between heads and manifold increases. You'd need a thicker inlet manifold gasket.

DaveEFI wrote:If you lower the compression ratio by using thicker head gaskets, the clearance between heads and manifold increases. You'd need a thicker inlet manifold gasket.

Yes your right my mistake ,is it possible to get a thicker inlet gasket so I can use a composite gasket with my sd1 heads ??

Not to confuse things! My setup:
measured 9.4:1 CR, 4.6 block, standard pistons, intercooler and mapped spark/injection running 10psi and works great, no detonation.

Haven't had the power measured but i'd estimate 350+

There are downsides to lowering the CR lower than required in that you loose drivability off boost and lower efficiency.

Tom.

Standard 14 bolt - large chamber heads

Also bear in mind that as well as the piston bowl the pistons do not come all the way to the top of the bore.

SuperV8 wrote:Not to confuse things! My setup:
measured 9.4:1 CR, 4.6 block, standard pistons, intercooler and mapped spark/injection running 10psi and works great, no detonation.

Haven't had the power measured but i'd estimate 350+

There are downsides to lowering the CR lower than required in that you loose drivability off boost and lower efficiency.

Tom.

Thanks for the info not sure if my 3.9 pistons will take 10psi I would be over the moon with anything near to 300hp ,just want to get the block built up so I can get it back in the car and free up some space in the garage so I can get on with the rest of the job

Darkspeed wrote:Standard 14 bolt - large chamber heads

Also bear in mind that as well as the piston bowl the pistons do not come all the way to the top of the bore.

Is that measuring 33.6 ? I suppose the brand of valves fitted might change it a bit as well, I've seen some valves that have a big dimple in both some have a small dimple and a large dimple and some don't have a dimple in them at all

Thanks for the info not sure if my 3.9 pistons will take 10psi I would be over the moon with anything near to 300hp ,just want to get the block built up so I can get it back in the car and free up some space in the garage so I can get on with the rest of the job

I was just trying to show don't get too hung up lowering the CR, using thicker head gaskets or low CR reducing plates also have their negative effects of reducing squish (more squish the better).
As long as you are not heating the air too much (using an intercooler) and have good tuning/control over spark and fuel then 10psi isn't a lot.
Do you know how much boost you need to make 300bhp?
Using various engine calculators when I was doing my supercharger install I estimated I needed arround 12psi to make around 400bhp
With my original (standard) 3.5 and first supercharger install I only got up to 3psi (due to belt slip problems) even that made a big difference.

Tom.

Having spoken to a man who has cc'd hundreds of RV8 chambers the 14 bolts usually come up around 33.5cc give or take .5cc
- 7-8cc for a composite.

If going turbo it may be worth considering having the exhaust ports taken out a bit as they are quite restrictive.

When I did my last low compression RV8 build for boost + nitrous I bought a set of Omega Forged pistons with a lower compression height for my 3.9 block. This not only saw my pistons 7mm down the bores at TDC to give me a 7.5:1 CR. It also gave me a bigger chamber size to fit more charge into. The results were stunning to say the least

Ok so the numbers are in, I know the cr, it's been to john eales ,the block was lightly skimmed to remove a scratch that happend in storage they put a piston in to check the capacity with standard 9.35 piston then added the capacity of the head gasket (cometic) the head skimed to make them straight the cr is now 8.93 to 1 so under 9 so should be ok with the moderate boost I plan on running
John says the inlet manifold should still fit