I have read some specs on some of the serious strip style CTD's and noticed in several builds the compression ratio is lowered. What is the reason for that? When I built some big block Mopars in my single life, I would usually raise the compression ratio to any where between 11.5:1 to 13:1 depending on the streetability desired and diesels are much higher. How does the diesel compression ratio affect performance?

I know this is lengthy, but I haven't been able to find out anywhere else. Thanks for your time!!

 

When you lower the compression, you can stuff more fuel and air in there.

 

I lowered mine just a taste for nitrous.

 

Were you running turbos on those big blocks? ;-)

They lower the compression so they can turn up the boost. Same is done on turboed and sc gassers.

 

It's all about cylinder pressure. Cylinder pressure makes power.

Static compression is only part of the equation. By lowering the static compression, the turbo can work a little more efficiently, and increase cylinder pressure quicker. That gives you more power off the line.

 

Most of the "big boys" running the GMC 6-71 blowers are around a 6.5-1 CR. You need room for all the fuel and air being stuffed into the cylinder. Run too high a CR or too much boost and you can pop the jugs, at least on a radial engine!

 

It's really more about being able to run more boost than "running out of room for the additional fuel and air." I agree with what .boB said.

 

Thanks for the replys. I always ran naturally aspirated & never got into the blowers & stuff. Putting it in comparision with the blown engines that lower thier cr makes sense!! Thanks!!!!!

 

Friend of mine built a real nice drag car with a high compression big block. He added a blower and couldn't figure out why he had to underdrive it to get it to run OK. I asked him what pistons he went with and I got the deer in the headlights look
Engine came out, new lower CR slugs went in, he ran the blower 10% overdriven and had a screamer!!