compression ratios

[navyblue2000]

as a general rule, how much does .1 compression add? eg, 9.7:1 as opposed to 9.6:1 hp and tq wise?
it seems with the soon to be aquisition of the 86 TA, the V6 is gonna say NA, but how high can i go with compression with 93 octane?

[RiceCooker]

<blockquote>quote:</font><hr>Originally posted by navyblue2000:
as a general rule, how much does .1 compression add? eg, 9.7:1 as opposed to 9.6:1 hp and tq wise?
it seems with the soon to be aquisition of the 86 TA, the V6 is gonna say NA, but how high can i go with compression with 93 octane?<hr></blockquote>

Not sure but I've heard that it adds approx 10% more hp per full point (ie: 9.4 to 10.4). I wouldn't go higher than 10.5, maybe 11.0 for 93 octane

[black34v6]

really easy to figure this out...

THIS IS JUST A FORMULA FOR ESTIMATION
this is not a "what you will get" formula, but here:

%gain=(upped CR-stock CR)/stock CR

so, if i wanted to see how much going from my 3.4's stock 9.0:1 - 10.4:1 would be:

%gain=(10.4-9.0)/9.0
%gain=1.4/9.0
%gain=.15

and then take the .15, and do this:

hp/(.100-%gain)=hp after CR raise or,
160/(.100-.15)=hp after
160/.85=188.24

so there ya go. little bit o math that seems to give estimations. i havent tested this little match theory out in real life on a dyno, but im sure someone will after this ;)

-R

[ December 11, 2001: Message edited by: Russell ]</p>

[Rik]

Just happens I was leafing through the latest issue of Car Craft at Publix, and they have an article on this very subject. They took a 440 Mopar engine and tried it at different compression ratios to see how much difference there was. They used specially made copper gaskets to lower the CR; there was some worry that it wouldn't seal perfectly when they got too thick, but everything worked fine. No leaks whatsoever.
Starting with an 11.0:1 ratio, the engine dynoed at 501 horsepower. Sorry, don't remember the torque.
Adding a thicker gasket and lowering the CR to 10.0:1 dropped power to 483. At 9.0:1 it was 460, and at 8.0:1 it bottomed out at 440 horses.

Going in, they said the "rule of thumb" is four percent difference in hp per full point of CR. So on a 500 hp engine that would be about 20 hp, and that is just about exactly what happened.
So, theoretically, on an otherwise stock 3.8 engine, going up to 10.4:1 should be good for about eight horses. No idea what would happen with the Supersix package added into the equation.

Rik