compression guesstimating..

[DeftAnesthetik]

my 4a has had some extensive work done on the head and bottom end. the previous owner had it bored out and a full race port done on the head. my problem is i have no idea what its been bored to, what the combustion chambers cc out at and what thickness head gasket is being used, the pistons have been upgraded to forged(or semi-forged).... now im getting ready to put on the autronic unit i've had for a while and as such need as much information as i can to program into the unit for peak performance, is there anyway i can get a rough idea of compression ratio by doing a compression test?

also.... say you have a completely stock bigport 9.4:1 comp engine running the factory headgasket (1.2mm compessed i believe) and change to a 0.8mm head gasket, leaving everything else, what kind of jump would be expected in compression?

i really do not want to pull the head off to find what i've got, i do however have a couple of copper headgaskets i got from ebay i would eventually like to use. one will be going to the 4agte im building the other will go into the 4a im running everyday (if its worth the trouble) since the bore opening on most headgaskets is the same the only variable is the thickness im trying to find out what its worth (in compression ratio) per 0.1mm of gasket.

since i dont know the exact specifics of my current setup i really only need a "generall this is what to expect" answer

[oldcorollas]

it all depends on the cam, as that will change dynamic compression even at crankign speed.

ie.. depending on cam, your car with 10:1 compression might have 140psi or 210psi.

why does the autronic need CR for programming?

just calculate the changes you are talking about.
(combustion chamber + HG volume) / (swept volume + combustion chamber + HG volume)

in which case, you need the bore

why not ask the previous owner?

[jeffro ra28]

The compession test is affected by things such as ring seal, port flow, manifold flow, camshaft design, static compression, valve seal and cranking speed of engine. So NO you CANNOT calculate engine compression by doing a compression test.

You could however CC the engine assembled at BDC and TDC and work outa very close static compression from that information. However that is provided the CC fluid does not leak past the rings. A few measures would have to be taken to prevent this.

[30psi 4agte]

Im with OC ..... the computer doesnt need to know what the comp is at..

Your tuner should beable to tune the car regardless of it compression ratio.



P.S. i love it when i hear the term " full race"