You guys with stage 2 cams

[1993MTXSHO]

Does running stage 2 cams lower your compression at all? Has anyone done a before and after compression test?

If you have stage 2's and have run a compression test please post your results as I am curious.:thankyou:

 

[SuperHO]

last i heard, cams don't have anything to do with compression ratio...that's all in the pistons and combustion chamber design.

 

[1993MTXSHO]

last i heard, cams don't have anything to do with compression ratio...that's all in the pistons and combustion chamber design.

Well usually they don't, unless you have really nasty cam. Reason being the overlap and lift is so high that the piston actually starts coming up before the exhaust valve is fully closed. Therefore lowering compression. The compression will come back up at higher rpm however due to airflow characteristics. So the compression test will read lower at lower rpm. This is the reason for low end tq loss and high rpm hp gain with bigger cams.

Now the stage 2 cam's aren't THAT nasty by some standards, but I was just wondering if they actually do anything or do they close in time?

 

[Phoenix]

Havnt tested that out yet , but interesting question though.

 

[St Louis SHO]

Wrong. Compression is not affected. Cylinder pressure is. They are 2 different things.

Edit: Unless someone shimmed (or) adjusted valve lash too tight...

 

[1993MTXSHO]

Wrong. Compression is not affected. Cylinder pressure is. They are 2 different things.

Edit: Unless someone shimmed (or) adjusted valve lash too tight...

If you want to get all technical yes, it is cylinder pressure. Technically a compression tester is not a compression tester, is is a cylinder pressure tester.

Anyway, is "cylinder pressure" effected by stage 2 cams?

 

[jonmon6691]

The exhaust valve closes well before the beginning of the compression stroke. The intake might still be closing while the piston starts moving up. This would be nearly negligible at running speeds but would show up during a cylinder pressure test.

I was under the impression that low-end loss was caused during the intake stroke when the exhaust valve as still open, and some fuel-air mixture is allowed to escape.

 

[NovaSS]

CR ( static) is base on the mechcanical design of the engine, it is not changed by cam design or cam changes.

Now google dynamic compression ratio.
This deal with the effects of cam timing while the engine is rotaing. It will be lower then static CR

 

[1993MTXSHO]

CR ( static) is base on the mechcanical design of the engine, it is not changed by cam design or cam changes.

Now google dynamic compression ratio.
This deal with the effects of cam timing while the engine is rotaing. It will be lower then static CR

Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.

So do the stage 2 cams close in time before the piston starts rising? Or do we lose a hair of compression when running them?

 

[SeanMc]

Other than running rich and destroying cats every couple years, I've haven't had any problems with them.

 

[1993MTXSHO]

Other than running rich and destroying cats every couple years, I've haven't had any problems with them.

I'm not talking about issues I am just wondering if there is any loss. They're already in my car, so I am trying to figure out where abouts my compression should be for a healthy engine with stage 2 cams.

 

[SeanMc]

I'm at 180 with high compression (10.5:1), and Stage 2s in all 6 cylinders. I remember being in Utah at Bonneville, and it was the same with Ernie's 12:1 car.

 

[yamahaSHO]

Altitude will affect those readings as well. Those camse really shouldn't have much or any effect on a compression test. Keep cranking until the needle stops.