How does compression relate to HP if at all. I just thought about ti the other day. For example If a stock s5 motor has 160hp and 120:120:120 from the factory. Then would that mean that a s5 mototr making 100:100:100 is making less than 160 HP with no other diffferences.

MAybe its all in my head but I figured Id ask and see.

 

uhh...

have you ever taken an empty soda bottle and squeezed it as hard as you could and then loosen the cap really quick to send it flying? the harder you squeeze the farther the cap will go right? you are compressing the air in the soda bottle. squeeze it a little bit, low compression. squeeze it really hard, high compression.

the more air you can pack into the combustion chamber the faster and harder the rotor (like the bottle cap) will spin or the piston will go up and down. the harder and faster the rotor spins, the more power the engine creates. so hopefully that made sense and you understand how horsepower relates to compression....

 

Yes, lower compression will reduce power output. At what ratio, I don't know. I would imagine that there is some sort of formula for that.

I rued the day in the early 70's when most of the auto makers dropped the compression from an average of 10:1 to 8.5:1 and hp out went in the crapper. Those are actual numbers for the 70 and 71 383's that Mopar put in the Roadrunners.

 

You're talking ideal case ignoring a LOT of other variables.
The answer would be useless in real world terms.

Basically it's a 17% drop in compression, so it should loosely translate into a 17% drop in BMEP.

It looks like it's a direct relationship between BMEP and HP, so your HP would theoretically drop 17%...
http://www.land-and-sea.com/articles...lk_article.htm


-Ted