80cc Heads

Shaolin Crane · Nov 26, 2009

Is there a company out there that makes an 80cc combustion chamber head for a SBF? or if the head manufacturers would do a custom job and make me a set of head with an 80cc combustion chamber? all help is appreciated

srtthis · Nov 26, 2009

biggest afr is 72
biggest trick flow is 70
biggest brodix is 68

liljoe07 · Nov 26, 2009

Posted via Mobile Device

Next question is why in the hell, would you need an 80cc head?

srtthis · Nov 26, 2009

my guess would be a change of direction to lower compression with out haveing to get new pistons...

liljoe07 · Nov 26, 2009

True, but that should only be for a boosted application, technically. Many ways to get around a higher compression with boost. More than likely cheaper than buying a new set of head and having the chamber re-done.

Unless he has a set of heads like the AFR's with the 72cc , then 8cc is do-able in the chamber. Most guys dont have the compression they think they have.

Shaolin Crane · Nov 26, 2009

I was doing calculations last night for my new engine, and as far as i can see my static compression ratio is going to be 9.46:1 and that a tad higher than i want for boost, for some reason now i cant remember why i went with these pistons for a boosted application, my guess was the price i got on the entire kit
unless im doing my math wrong
-4.0cc flat top pistons
3.4" stroke
5.4" rod
MLS gasket thickness .040"
for my boost application i'd like something closer to around 9.0:1 or less, hence why i would like a large combustion chamber head
and no i dont have the heads yet thats why i was asking

liljoe07 · Nov 26, 2009

Do you know how far the piston is in or out of the bore? And what the headgasket bore diameter is? You also have to account for the ring land being below the top of the piston. Most guys dont, and thats why I said that most guys dont have the compression they think they have. It usually a little less.

Shaolin Crane · Nov 26, 2009

liljoe07 said:
Do you know how far the piston is in or out of the bore? And what the headgasket bore diameter is? You also have to account for the ring land being below the top of the piston. Most guys dont, and thats why I said that most guys dont have the compression they think they have. It usually a little less.

piston sits completely flush at the top of each bore, headgasket bore diameter is 4.040 at .040 thickness

liljoe07 · Nov 26, 2009

The Dynamic Compression ratio is going to be lower. Has everything to do with the cam. In other words, if you had a CR of 9.5:1 with one cam, then switch cams that had a different Intake valve closing, then the amount of cylinder pressure could be different, resulting in a Dynamic compression ratio lower. The DCR is what the engine actually sees. Static Compression is just a calculated number.

On the static compression, I came up with the same as you did. So your math was right.

liljoe07 · Nov 26, 2009

Also factor in that the pistons may say -4cc. Ive heard some measuring out to be 7cc. They can often be more than advertised. Then add in the space between the piston and cylinder wall above the top ring land thats about 2.5cc depending. You could very well have 5-7cc more in that alone. Which should put your static compression in the range you are looking for if thats the case. Thats with the AFR head with a 72cc chamber.

Shaolin Crane · Nov 26, 2009

liljoe07 said:
Also factor in that the pistons may say -4cc. Ive heard some measuring out to be 7cc. They can often be more than advertised. Then add in the space between the piston and cylinder wall above the top ring land thats about 2.5cc depending. You could very well have 5-7cc more in that alone. Which should put your static compression in the range you are looking for if thats the case. Thats with the AFR head with a 72cc chamber.

the probe **** is pretty dead on i can easily clay fill or silicone fill the relief cuts to see what they are exactly

80cc Heads

Shaolin Crane

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srtthis

the guy doing it does every local racers rear end

liljoe07

srtthis

the guy doing it does every local racers rear end

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Shaolin Crane

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Shaolin Crane

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