irocfreak

Ive heard that how high or low your compression is will affect the kind of cam you choose. Could any one confirm this and explain exactly how it works? i plan on using an lt4 hot cam with my motor, which currently is at 10:1 compression. Would there be a problem with this or is there a better cam out there for this compression? Any input would be appreciated.
Thanks,
Dane

Stekman

I have heard that you should run a higher duration for higher compression engines so you can tame detonation. Again, this is just what ive heard, if you do a search, im sure this has been brought up before.

Air_Adam

I've heard that too, but the other way around: that with a high duration cam, you should have a high compression ratio too. I think (not totally sure though) this is because with the increased duration, you get increased overlap. More overlap means that more A/F charge comes in the intake and immediately does an about face out the exhaust, which lowers cylinder pressure, and you need the higher CR to make up for that.

But, like I said, I'm not totally sure about that, its just the way I've come to understand it.

Stekman

You should be fine with that compression. Remember the HOT cam was designed for use in the LT-series engines. Stock, those run around 10:1 compression.

as for the duration vs compression, i think the BEST way to say it is that they go hand-in-hand. And yes, as you raise the duration (assuming the LSA is a constant), the overlap increases. My cam is a perfect example.

F-BIRD'88

Don't choose a cam based on the compression ratio.
Or to "tame detonation".

Don't try to run a motor with a high compression ratio by over camming it. thats a bandaid solution that makes for an inefficient motor.

Choose a cam that will work well with the induction and exhaust systems to make power (torque) in the rpm range you want to drive in.

Then; design your engine to be as efficient (compression ratio) as is practical, ( fuel grade {octane}, availability, cost).

ME Leigh

You want to choose the compression ratio after you already decided on a cam, and exaust and ...


Meaning if your setup can only support a XE256 run 9:1 compression. If your setup can support a XE286 run 10:1. ETC...

You want the dynamic compression ratio around 7.7:1 for optimum effeciency without detontation problems.