Ok here is my delima, I am currently in the process of building a iron block408. However I need a little help deciding on what compression ratio is acceptable or common on these engines. My car is a weekend play pretty that I want to be able to run on pump gas. What are your thoughts?
Heads and cam have still to be determined, as I need to pin point this issue first, then I can build them around that.

 

Well done come stock with 10.9-11:1 so maybe up a little from there since it's a pump gas setup. . Now if you were going E85 I would say 13-14:1

 

Depends on the cam and your cooling system. If you have a big nasty cam in there, your IVC will be late and you won't build as much cranking compression. So it's a good idea to throw more compression at it to build torque and make it more streetable.

More compression generates more heat as well, so having a good cooling system that can keep everything running optimally will also help fight off pre-detonation.

What cam are you going with? Need specs at .006" of lift, not .050".

 

JakeFusion, Sorry pal but I am not exactly for sure yet on the cam. I was thinking about getting up with Martin@ Tick or Brian @ Brian Tlloet Racing and have one of them spec me one out. Still up in the air. I was told that I needed to decide on exactly what compression ratio that I wanted, then have the cam built around that.

 

Well anyone else want to chime in? I have to decide by Tuesday.

 

10:5 that way you can still make power N/A or Boost it.


Nitrous doesnt care though

 

Joke's advice was dead on. The larger the cam you run, the more compression you'll want to run to make it streetable. To the point of running pump, dynamic compression, which is determined by your cam and static compression will be more important than static compression alone. The more overlap your cam has, the more static compression you'll bleed off allowing you to run pump gas. Personally, I'd statically shoot for Static in the 11.5:1 range and dynamic in the 8.5:1 range. You'll be fine on pump, and have a fun street car!

 

427zm, Thanks for the input, it appears that I should be between 11.5~11.8, depending on exactly how much my block will be decked.