Compression Raito?

[Mr GT 02]

ok this may be a retarded question for u pros.
But what does the compreesion ratio mean? and what is it for 02 GT's???

 

[chimchim]

I'll do my best. It's the ratio at which the charge of gasoline and air is compressed in the combustion chamber (the area where your piston is at TDC and your valves are closed). Laying on your garage floor that little big of gas and air is at a 1:1 ratio, but inside your engine the charge is compressed down 9.4 times as much as the outside barometric pressure. I think 99-04 are 9.0:1 or 9.4:1 ??? This compressed charge makes the explosion that forces your piston downwards that much greater. A "high compression" engine will make more power, but if you get around 12.0:1 or higher, you run the risk of blowing your head gaskets or worse.

EDIT: You can get higher compression by using flat top pistons and or shaving or milling the base of your heads to create a smaller combustion chamber. You can reduce compression by using dished pistons and or using compression reducing (read: thicker) head gaskets to create a larger combustion chamber.

 

[Mr GT 02]

what is the air/fuel ratio suppose to be at???? and say u are running lean..how do u fix that????

 

[chimchim]

I'd say 13.0:1 for N/A and about 11.5:1 for power adder. Just a guess. If you ARE running lean, you could add bigger injectors or a fuel pressure regulator, but those are physical things and guesses at best. A custom tune is the best and safest way to do it.

EDIT: I had my car dyno'd with an A/F before my tune and it was about 13.5:1 at 2000 RPMs and steadily dropped to 11.3:1 at 6000 RPMs. It feels like my tune fixed this, but I will comfirm it on the dyno soon. Why are you asking these questions. Most cars are a little rich from the factory just to be safe. Usually anything you do on the intake side with make your car lean and anything you do on the exhaust side will make it rich. It looks like you have a good mix of mods. You're probably OK with the stock tune.

 

[n0v8or]

Compression ratio =
volume of cylinder above piston with piston at top of the stroke divided by volume of cylinder above piston with piston at bottom of the stroke.

 

[Mr GT 02]

I'd say 13.0:1 for N/A and about 11.5:1 for power adder. Just a guess. If you ARE running lean, you could add bigger injectors or a fuel pressure regulator, but those are physical things and guesses at best. A custom tune is the best and safest way to do it.

EDIT: I had my car dyno'd with an A/F before my tune and it was about 13.5:1 at 2000 RPMs and steadily dropped to 11.3:1 at 6000 RPMs. It feels like my tune fixed this, but I will comfirm it on the dyno soon. Why are you asking these questions. Most cars are a little rich from the factory just to be safe. Usually anything you do on the intake side with make your car lean and anything you do on the exhaust side will make it rich. It looks like you have a good mix of mods. You're probably OK with the stock tune.

Oh im just asking questions (learning) lol

 

[chimchim]

Oh im just asking questions (learning) lol

hahaha And I'm FOS! I don't have any real-world experience myself. I just read and search too much. The thing to remember is that all cars are different and all cars react differently to mods. A dyno-tune is really the only way to truly tune your car to it's potential. If my A/F doesn't come out like I want, I'll be making a trip to Kauffmans Motorsports in Carlisle, PA this summer.