Lets say to raise the cr from 10.6:1 to 11.6:1. How much hp would I add from this?

 

I'd say about 5-7ft/lbs.,maybe 2 or 3hp.

Biggest difference will be in the low to mid range torque.

If you have large cams, you'll probably see an even larger gain.

 

How much will I loose when going from 11:1 to 9:1? Only 7hp???

 

You'll lose a bunch.

Compression works in diminishing returns.

For example, take 2 motors. One with 9:1, and one with 11:1. Raise the compression on both to 11.5:1 and the first motor will have huge gains.

Second motor will see little to none.

Once you get to a certain point of compression, timing becomes an issue and in essence, you're actually going to be LOSING potential HP by retarding timing in order to keep it running properly.

I'd say you'll lose about 10-15hp.

 

Let's not forget ... he's running boost.

 

Here is the results of going from 9.6:1 to 11.4:1

 

Well.....when I look at this dyno plot, it is not of an big deal to lower cr to 9.5:1 or 9:1 when I run 8-10psi.

 

Thats not as bad as I thought it would be

 

Everymotor is different so the gains or losses could be more or less.

-Alan