Hey guys I have a few questions about engine compression. Im selling my 79 z28 since I've decided I want a 70-73, and since I never started on that engine I was wondering about some things to do for the new one. Okay so for an engine with say a supercharger you would want a lower compression, and without one you would want a higher compression right?. Well me being a noob my question is what is compression, what does it do?, and does it determine how high your engine will rev?. Lets say i take a 350 and put 327 heads on it [note i dont even know if this is possible for sure cause well i just dont know] that would raise the compression ratio correct?. If having a higher compression gets more power out of the same amount of air and gas mixture would that make it more efficient?, but is engine nock a problem with a high compression engine if ran on cheap fuel?.

 

Ok compression is determined by the volume of the cylinder head chamber, any voids (valve relifes) in the piston, and the volume of the head gasket. Two ways to raise compression are dome piston or a smaller chamber. Either way you are taking all the air/fuel in the cylinder while the piston is a BDC and compressing it into a smaller or larger space. This makes compression go up and down respectivly. The tighter you can pack the mix in there, the greater the explosion. The bigger the explosion the more force there is pushing the piston down. Think of it like holding a firecracker flat in your hand, it just pops. Close your hand and pow, your on your way to the hospital.

Most chevy heads are either 64cc or 72cc and some are 58cc. Not sure about the 327 size. Blower motors like around 7.5 to 8.5:1. A good street motor with iron heads will max out at around 10:1 on 97 octaine. The same motor with aluminum heads might get away with 10.5 or even 11:1 with a good tune. I'm no expert on this, all I can do is rehash a bunch of stuff I have read over the years.

 

To put compression in simple terms, it's the difference in cylinder volume (plus head chamber size) between when the piston is at Bottom Dead Center and Top Dead Center. If BDC volume is ten times greater than TDC, then your compression ratio would be 10.0:1.
You would have to check the casting numbers on the 350 and 327 heads to know what chamber size they are. The 327 and 350 engines have the same cylinder bore diameter. If both heads have the same chamber volume, you won't be changing your c.r.

 

thanks guys that puts it into perspective for me

 

Glad to help