Cylinder pressure

[hysteric]

Does increasing the cubic inch capacity of an existing engine but retaining the same camshaft increase the cylinder pressure?

Same opening and closing points but in a bigger engine. Thoughts?

[rebelrouser]

Use an engine program and change the bore and stroke and see what it does to the compression ratio. I think you will see that it increases the compression ratio, and thus more cylinder pressure.

[mag2555]

How could it not, but in terms of making the best power it may require a Cam change in regards to the overlap numbers.

It will also increase the vacuum level.

[pdq67]

I want to say that if you use a small cam that is in a small engine in a bigger engine that the pressures will go up. Same CR here.

I might be wrong but one case in point is no more than Chevy's great old -929 hy-cam that has been installed in 195hp/283's all the way up to the 265hp/400 as a base cam and it has, imho, done fine for its intended applications.

Ratio-wise, a bigger engine needs to bleed off some pressure or detonation might happen. And this is one reason bigger engines cams are bigger!

I seem to recall that Crane might still be using engine size to spec SOME of their street cams.

i want to say their, "Blazer", series, but it has been years since I looked?

Please kick away.

Thanks,

pdq67

[F-BIRD'88]

Are you refering to cranking pressure or dynamic real cylinder pressure running at rpm speed at WOT?

Basic cranking pressure is determined by intake valve closing point and also some what by cranking rpm.

[steve cowan]

I tried to screenshot some SIM photos off engine pro,but they did not turn out good enough,
I changed bore refence from 4.03 to 4.125 including cylinder head bore reference.
There is no yes or no answer to your question,so many variables changed.
Estimated cranking compression stayed the same but what does that really mean?.
torque and hp curves changed,peak values changed,piston speed changed,throat/ bore ratio changed and other simulation recommendations changed as well,first thing that I thought off was less heat in the combustion chamber leading to less thermal efficiency but again it's really a loaded question

[David Redszus]

I tried to screenshot some SIM photos off engine pro,but they did not turn out good enough,
I changed bore refence from 4.03 to 4.125 including cylinder head bore reference.
There is no yes or no answer to your question,so many variables changed.
Estimated cranking compression stayed the same but what does that really mean?.
torque and hp curves changed,peak values changed,piston speed changed,throat/ bore ratio changed and other simulation recommendations changed as well,first thing that I thought off was less heat in the combustion chamber leading to less thermal efficiency but again it's really a loaded question

Using your engine specs, plus a few more, we can easily answer your questions.
B = 4.030, S = 3.75, IVC = 114 deg, SCR = 10.01, DCR = 7.94, Pressure @ TDC = 267 psi
B = 4.125, S = 3.75, IVC = 114 deg, SCR = 10.44, TCR = 8.27, Pressure @ TDC = 283 psi
the chamber volume has remained unchanged.

Changing the cam to alter IVC will result in the following:
110 deg= 270 psi
114 deg= 283 psi
118 deg= 295 psi