camshaft question

[kever65]

Hello loungers,

question for the engine specialists,

lets say you have a 1776cc (69x90.5), with fk 10 cam, peak power at lets say 7500rpm,  and easely pulls 8000rpm and you have the complete same setup in an 2332cc will the peak power and max rpms be the same, or do you need a cam with more duration? Or is it the heads in combination with the cam who determines that. So when you don t change the heads both rpm numbers will be lower.

curious what the explanation is

[MattiK]

I'm not specialist, but I have one example.
I had 69x94 and changed only crank to 82. Same cam and heads. Peak power went down about 1000 rpm. Bigger engine need more air, heads are limiting.

[kever65]

What heads were you using?
If they were able to flow the air needed for the bigger engine than the rpm's would be the same?

[MattiK]

What heads were you using?
If they were able to flow the air needed for the bigger engine than the rpm's would be the same?

In principle, yes. But there is also other factors. Carburetors and exhaust at least. I had in my 82x94 engine bigger venturis and better flowing exhaust. So I know the heads were limiting factors. I had CB044 round ported heads with 40 x 35.5 valves.

[Udo]

Hello loungers,

question for the engine specialists,

lets say you have a 1776cc (69x90.5), with fk 10 cam, peak power at lets say 7500rpm,  and easely pulls 8000rpm and you have the complete same setup in an 2332cc will the peak power and max rpms be the same, or do you need a cam with more duration? Or is it the heads in combination with the cam who determines that. So when you don t change the heads both rpm numbers will be lower.

curious what the explanation is

You need defenitly bigger heads - cam like FK10 is ok for an engine like that if you go on the street

Udo

[kever65]

Ok, so you are saying that the cam will act more as a street cam, udo (with the bigger heads), so if i understand correctly, the rpms where peak power will be produced will be lower than in the smaller engine ?

[Udo]

Yes in any case with that cam . For a 1776 it is a very big cam - may be too big. and for your new combi you can choose a bigger if you want and the heads can handle it. Most important are the heads

Udo