Jonboy2389

What is the highest compression piston i can use on my 89 gt 5.0 without changing the computer, any help is appreciated, thanxx.

imnotmy77stang

well, you'd wanna stay at around 10:1 if you want to run pump gas. there are mutilple brands you could go with, but the best bang for the buck may be the keith black domes which are like a little over 300 per set, or some forged trw slugs but they are heavier than more expensive pistons such as products from JE, SRP, Mahle, Diamond, etc

Jonboy2389

ight cool do u kno if i have to change the computer, id like to bring em up to 11to 1 compression pistons. and if i can without changing the computer what octane should i use?

mjr46

kb pistons with a .200 dome and 58 cc heads will put you at 11 to 1 and you can run pump gas as long as you have aluminum heads...been there done it on my last 306.....worked great until I decided to juice it!@![:@]

imnotmy77stang

LOL

those same pistons with a later model 5.0 head (E7's) should be 10-10.5ish which is perfect

tinman

Jonboy; what compression you can run kind of depends on the air density.
What part of the country are you in?

5spd GT

The main factor is not just static compression, but the dynamic compression, which is dictacted by the camshaft valve events.

You can run a 9.8:1 engine and have to run race gas, or a 11.5:1 engine and be fine with 93 octane (pump-gas).

It is not as simple as piston/combustion chamber volumes.

Good Luck!

imnotmy77stang

^ not but its a hellofa good place to start.