with many ways to increase horsepower in our motors one specific thing has puzzled me and id like some intelligent enlightening. i hear alot of compression talk in here, but are the actually adds to HP and TQ vs reliability and being practical. if i were to raise my compression a full point what kinda increase would i be looking at and how would it effect my potential of a power adder (turbo SC nitrous oxide). with keeping in mind daily driven.
i was wondering the same thing. anyone?
Ahhh, compression. Higher compression makes power with more aggressive camshafts. How much more? Hard to say. I would say around 11.5 to 1 with a very aggressive camshaft might be the limit. Your camshaft spec card should have a listing for sugguested compression ratio. And I would not use a thin head gasket to increase compression. This can start detonation whereas if the compression were increased via the dome on the piston, or squaring the decks on your block, it probably would not detonate. You need the cam to bleed off some of the cylinder pressure, which means as the rpm picks up, it turns into more power. Know that if you do build a motor that is over 10 to 1, you may need to mix in some race fuel(with ignition timing set normally). I used to keep the timing set down when driving normally; and put the timing back up and mix race fuel when I was going to run the car.
So, lets say in a LS engine that is otherwise stock, would there be a noticable (if any) increase with using say a pr3 piston? I realize that using a cam designed for that higher compression would obviously reap more benifit, but would you suggest to someone rebuilding their engine who had a set of pr3 pistons lying around (and was going to otherwise leave their engine stock) to use those pr3 pistons or to just sell them?
I would be interested in someone’s testimonial regarding a stock motor vs stock with 10.8:1 pistons.
Originally posted by pml
Ahhh, compression. Higher compression makes power with more aggressive camshafts. How much more? Hard to say. I would say around 11.5 to 1 with a very aggressive camshaft might be the limit. Your camshaft spec card should have a listing for sugguested compression ratio. And I would not use a thin head gasket to increase compression. This can start detonation whereas if the compression were increased via the dome on the piston, or squaring the decks on your block, it probably would not detonate. You need the cam to bleed off some of the cylinder pressure, which means as the rpm picks up, it turns into more power. Know that if you do build a motor that is over 10 to 1, you may need to mix in some race fuel(with ignition timing set normally). I used to keep the timing set down when driving normally; and put the timing back up and mix race fuel when I was going to run the car.
where did you get most of your info? I don’t think you are going to notice a difference in detonation between raising the compresion with pistons vs milling the head vs a thinner head gasket (in fact a thinner head gasket and milling the head are essentially doing the same thing). But its pretty much agreed upon that pistons is the best way to increase compression.
how high of compression you can go safely is going to depend mainly on what type of gas you plan on running. Here in cali you can only get 91 octane (however i’ve heard that because of the additives its actually more like a 92… they just can’t call it that), and i’m planning on running 11:1 in my motor. Another member is running the same thing and isn’t having any detonation problems here in cali. If you live somewhere where you can get 93 or 94 octane you could run an even higher compression safely. Although anything past 12:1 is getting to be borderline whether or not you would want it on a street motor.
it has been said that every .1 increase in compression yeilds about 1hp. so bumping up a full 1.0 would add 10hp. Of course this is a VERY general rule and is definitely not absolute. How much it will actually increase your hp is of course going to depend on all of your other mods (i/h/e, cams, head work, tuning…)
the tip about ignition timing and race fuel is a good one. If your compression is high you can retard the timing a little or set it to stock in order not to ping on pump gas. But for a little extra power when you need it you can advance the timing a little and add higher octane fuel.
Re: Compression Talk
Originally posted by dElPHilSvTeC858
how would it effect my potential of a power adder (turbo SC nitrous oxide). with keeping in mind daily driven.
if your gonna raise the c/r you can blow off the turbo idea. turbos need 8.5-9.0 c/r (low compression).
but the pr3 pistons come in 81mm(stock) and 81.5mm (oversized stock). tip. when rebuilding an engine it is sometimes needed to rebore the cylinder walls (hence oversizing the walls, now needing an oversized piston). another member schooled me on that.
Re: Re: Compression Talk
Originally posted by Speeddaddy
[B]
if your gonna raise the c/r you can blow off the turbo idea. turbos need 8.5-9.0 c/r (low compression).
but the pr3 pistons come in 81mm(stock) and 81.5mm (oversized stock). tip. when rebuilding an engine it is sometimes needed to rebore the cylinder walls (hence oversizing the walls, now needing an oversized piston). another member schooled me on that. [/B]
small correction… 81mm and 81.25mm if they are oversized you’ll see “25” on the top of them (at least thats how my p30’s came)
also, you can run turbo on higher compressions (like 10:1-10.5-1) but you just have to run less boost. Even if you’re running a low compression like 8.5-9.0 you may not be able to boost too heavilly if you’re still on the stock rods and pistons.
dElPHilSvTeC858: i suggest you look over turbo, nos and all motor applications before you decide to mess w/ your compression ratio. Decide which type of engine you want to build and then tailor your compression around that setup.
:werd: