silverado2000

i have a lq4 with 243 cast# heads what is the compression ratio with stock pistons?thinking of getting new piston, i want a higher compression but still want to be able to run on 93 octan.

Zick

iTrader: (18)

You should be around 10.5:1~ depending on what thickness head gasket your running.

I was at 11.5:1 w/ LQ9 243's & .040" cometics gaskets.
With my timing dropped I was able to run even 87 octane just fine.

But I also had a good size cam which I believe helped due to it not having as much cylinder pressure IIRC.

silverado2000

okay i plan on running the mti g1 cam 228 232 .588 .575 113, so i should go with a .040" cometics gaskets. would this be a good combo?

MGMC

iTrader: (46)

bringing it back from the dead. 10.5:1 on stock gaskets? what about with .040? im thinking about swapping in some stock 243's or 799's also

hirdlej

iTrader: (31)

Yes, you need to measure though how far your pistons are out of the hole. My LQ4 they're .013" out of the hole so with stock 6L head gasket and 243's I'm at 10.6:1 comp

MGMC

iTrader: (46)

what length pushrod are you running with that?

hirdlej

iTrader: (31)

Me?? 7.4"

hirdlej

iTrader: (31)

Maybe you are or I think you are misunderstanding me. All iron truck blocks have a loose factory tolerance of .004"-.016" of the pistons coming out of the bore. You need to measure yours first to appropriatly determine a proper head gasket and calculate your final compression. I cringe everytime I hear someone state "Yeah, I just threw a .040 head gasket on and called in good". If your pistons were indeed .016 out of the hole and you threw a .040 head gasket on, you'd be flirting with a broken motor. A .024" quench would be bad news. Please measure your pistons out of the hole before proceeding to purchase any aftermarket head gasket. Otherwise put a stock one on and not worry

MGMC

iTrader: (46)

yeah i most likely will run a stock gasket, i was just wondering the difference in compression between the two.

MGMC

iTrader: (46)

thats good info bro, thanks