Compression Questions

[Deuce]

1) How do you change engine compression? I see people saying what their compression ratio is, but I've never seen anything that says how to do it.

2) I know that if compression changes one way, HP output goes up, and mileage goes down, and vice versa. Would doing this change the amount of emissions out the tailpipe (and be a way to pass smog tests if necessary)?

[luisitol]

I can think of two ways that you can change compression:

1) Thicker Head Gaskets

2) Changing Pistons.....The size, shape, and combustion areas on the piston determine if the compression ration rasies / lowers


As far as HP and compression

Take a Camry...

The 5SFE makes 130hp with a 9.5:1 CR. Now if you were to raise that to 10:1 you would make some more horsepower. If you lower the CR to 8.5:1 you will go down in horsepower [all of this is also dependent on tuning]

HOWEVER, lower CR allows for you to to introduce more forced induction, i.e a turbo. So although your naturally aspirated HP rating went down, you can now add a Turbo and have much more the 130hp......

Hope that helped

[InTeReX]

Helped ME!

[Nick]

you mean thinner head gasket right....

if you have an inline engine one cheap way of upping compression is to shave down the head, they make raised pistons with notches for the valves

[luisitol]

Oldman....yea thinner is th e usual way, but technically thicker changes the comperssion as well

Interex....glad it helped someone

[Deuce]

i didn't know you replied...it helped a lot. thx

[88 LE]

Thicker headgasket would lower the compression ratio.

Thinner would raise it. Decking the head will also raise the compression ratio.

As far as pistons theres flat, domed, and dished.

[rezzle]

http://sdsefi.com/techmods.htm