Calculating 2jzgeT compression ratio

[p5150]

I think 3mm is too thick - it will drop it down to less than 8:1. You will lose bottom end torque and spool time but be able to run a bit more boost than a higher c/r motor without the fear of detonation or preignition.

In other words you will sharpen the curve of your dyno graph.

Do a compression check on your motor and see what you come up with. Aside from measuring out everything before you put it back together this is a great way to ensure that your calculations were correct and that your head gasket didnt compress more than they said it will.

Who knows, maybe your specs will be the exact same as a GTE?

 

[jmcboost]

So, I am just getting familier with the compression test/check on an engine. I have a gauge I can plug into the spark whole and crank the engine over with the starter and get some pressure that way. But how can this tell me about exact compression numbers? Or is there another compression check way? Let me know, I am very interested.

 

[p5150]

Yeah, usually a compression check is done when the motor is warm. Warm it up to operating temperature and then shut it off.

Thread or hold in the compression gauge in the spark plug hole (depending on what type of gauge you have). Crank the motor for a few revolutions. The pressure should build rapidly to a peak pressure on the gauge. The gauge should have an internal check valve that will hold the pressure until you release it. This allows you to check the peak pressure.

A turbo motor may have a compression ratio of 8.5:1 and have a cylinder compression test of 165 while a N/A motor with a 10:1 c/r may come out to be about 200 or so. A higher c/r will yield a higher psi. By looking at the psi of your compression gauge you can estimate what your compression ratio is.

If one of your cylinders is significantly higher or lower than the others it indicates that you have problem of sorts. Excessive carbon buildup in a cylinder can give you higher compression test results while leaking/worn rings, scuffed cylinder walls, leaking valves or a blown head gasket can give you a lower compression test result.

Be careful that you have a good seal from the compression gauge into the cylinder - a leak can give you a false "low pressure" indication.

 

[jmcboost]

OK, that makes sense. So do you keep cranking the engine untill you get the highest pressure that cylinder will produce, or do you just crank a couple of times?

 

[Supra_Villan]

any idea on the height of the head? i need to know for headgasket selection.

 

[Altezza576]

Guys, keep in mind the NA-VVti motor has a Higher Compression than the NA-OBD1(non VVti) motor. That is probably where the 10:1 compression number is stemming from. the 2JZGE (OBD1) motors may well have a 9:1 compression. I can get the specs from my MK4 factory service manuals if we need to clarify this?

 

[quickgs300]

I thought the VVTi model was 10.5.1 not 10.1?
So what is the CR of the stock GE, the head and block was never resurfaced!