RV8 5200cc compression ratio?

[kokkolanpoika]

Hi..

Need for advice/experience..

I have got Rover 5,2 engine with ~26cc pistons and heads are ~33-34cc, Quick measure in poor black plasticpiece.
i cleaned champers + slightly modifield champers near of valves + ultra big valves.. Thats why they are approx 33cc.
Head gasket thickness is about 1,2mm (97mm composite gasket)
So i just calculate that my compression ratio would be near 10,5-10,62:1?

My question is. Is this too low if i reach up 350-400hp limit? (target 370hp)
My cam is Kent M228. 280/290deg. Fuel:injecktion.

I spoke with Chris at Rpi, and he didin´t give me a good answer of this question. He only says that you dont need 11:1 Cr ratio if you want to make real power. You got same power with lower Cr also..

I think if i have got performance cam, then i need bigger Cr that std 9.35:1? I think 11:1 is optimally with my setup?

My heads need milling anyway, and thats reason why i ask this?

[CastleMGBV8]

Timo,

Are you sure that your piston volume is 26cc?

What is the deck (block face) to top of piston measurement?

The composite gasket compressed is approx 6cc

With your figures you have about 10.8/1 subject to how much your pistons are down the bores which will reduce the figure.

Kevin

[kokkolanpoika]

Timo,

Are you sure that your piston volume is 26cc?

What is the deck (block face) to top of piston measurement?

The composite gasket compressed is approx 6cc

With your figures you have about 10.8/1 subject to how much your pistons are down the bores which will reduce the figure.

Kevin

Yes 100% sure that they are 26cc, because i measure them today again. And when i order them by Ross, data cataloque says 25cc without valve pockets. + valve pockets about 1cc when i measure them at old 5,2 pistons..

Deck is zero.. (or maybe piston can be couple of thou over block face) Cant measure now, because block is in the machine shop.. They do honing work +valve pockets at 4 pistons..

[Mark]

Your cam seems a bit mild for the power you are after, I ran an M238 on my daily driver 4.5 Rover V8 and it was very tractable.
Made 333bhp on 450cfm Holley carb.

Mark