What difference does compression ratio make in regards to HP/torque??Like, what would the difference be between 8-1 compared to 10-1??
Would there be any “Pros” going with a lower compression ratio?? (excluding power adders??)
What about “Cons”??


Thanks!

arcaidy

 

Come one guys. Somebody has to have some input.

Thanks
Arcaidy

 

I am no super-genius but to the best of my knowledge, higher compression will help. The higher the compression ratio is, the harder the cylinder will fire. If you were to put gas/air mixture into a pint size paint can and ignite it you will do more damage to the can than if you used the same amount in a gallon size can. The explosion is more compact and powerful. Thus adding a quicker and more powerful power stroke. I don't know what kind of gains you will get though. Hope that helps.

Are you changing heads or pistons or what? Just curious.

 

I have a car that I've taken over as a project.. Its an 85 Vette. The stock heads are gone. I have a set of 462624's that have ben ported and S/S valves put in. They have a 76cc chamber. I am not sure what the stock ones were, but i know they were iron. The bottom end is stock. I was told that it probably wouldn't be a good idea to put the heads on the car. I took it at that.
I got to wondering then what would be the difference be. you always hear its good to increase your compression, but why. I can understand the idea behind it. I'd just like some input on how much it efects performace in the real world.
Arcaidy

 

I was kinda hoping we would get some educated responses here. I am going to build a sbc 400 and am trying to figure out what CR to run. How much is 1.0 of compression worth? And is it really "worth" it?

 

Yeah, there's going to be a BIG difference betweeen an 8:1 motor and an 10:1 motor. The higher compression creates higher pressures which means that the mixture will combust more powerfully. At certain points, cylinder pressure can create enough heat within the chamber to ignite the a/f mixture before the piston reaches the optimum combustion point, causing "knock" or "detonation" which will kill power and kill your motor. You want to run the most compression you can while keeping a safe "distance" from detonation. The amount of compression you can run depends on whether you have aluminum or iron heads (aluminum transfers heat away from the chamber=higher compression), how big your cam is (bigger cams relieve cylinder pressure well so you can run higher compression), whether or not you have a power adder (these create higher cylinder pressure), and the quality of gas readily available (high octane gas has higher flash point allowing further knock resistance). If you run less compression than you can you are just throwing power away. Some people say each compression point is equal to about 15 or so hp but i myself think the difference is a lot more. Higher compression also helps a motor rev higher because at those speeds the mixture isn't getting that much time to combust so its going to need all the help it can get.

 

as stated above compression is good, to a point then it causes problems. i believe the most current thinking on piston design and engine building for streetable engines is to use a small chamber and a dished piston to improve the squish area while still maintaining a decent compression ratio. the thing to keep in mind is that you can't just improve in one area since all the parts work together, it has to be a matched combination of parts. i "big cam" isn't much good without heads that can flow more air and the heads aren't much good without an induction system or exhaust that can flow an equall amount of air.

 

so in your opinions, what is an approximatly good compression ration on a 406 with iron heads? I know the other parts affect performance together, but just a close range. I have an idea of what I am thinking of running. But I want a little more feedback to see where I am at or where I should be.

thanks.