Toyota Engine Compression ratios - How they come from factory

[Matt]

Standard Factory Compression Ratios


4age


16v Bigport - 9.4:1
16v Small Port - 10.3:1
20v Silvertop - 10.5:1
20v Blacktop - 11:1


Gze


Supercharged GZE Bigport - 8:1
Supercharged GZE Smallport - 8.9:1


7a


7afe - 9.5:1

[dove grey 64]

was trying to work out what 9.4:1 would convert to in psi readings and found this on google

There is really no 100% accurate way to calculate your compression ratio from psi, but there is a formula that will get you fairly close. First take your psi reading and divide it by 14.7 (for example, psi reading is 170 divided by 14.7 = 11.56). Then take your engine size and multiply by .01 (for example 250cc x .01 = 2.5). Then add 1 to that number, so then you have 3.5. Last you will take the 11.56 that you got from dividing the psi reading (170psi) by 14.7 and subtract that 3.5 from the 11.56 ( so you have 11.56 - 3.5 = 8.06). And that is your approximate compression ratio (8.06:1). Like I said, there is no formula that will get you an exact reading just because it is virtually impossible, but that formula always gets you fairly close.



now im picking up my brain off the floor.
im pretty sure it works out to between 170psi to 199psi, anyone else know?

[Matt]

The actual numbers on the compression test can be influenced by a heap of different things... I've generally learnt that the variance between cyclinders must not be more than a few % otherwise you have a problem.

Leak down tests are also good, but not fool proof. You can tell allot by using a bore scope if you know what you are looking for.

[ke_70]

we adding to these?

[Matt]

yeah why not....

[Skid_KE70]

it would be interesting to see what compression ratio a silvertop 20v 4age is with smallport 4agze pistons. this seems to be a fairly common conversions for people wanting to go turbo with a low budget. i for one have used this combination and it worked well aside from it then being an "interferance engine" :)

[Matt]

I saw a comp test result on a 14:1 engine over the weekend and the result was up around 255psi per pot....

[lolwat]

my old bigport had 235psi across all 4, bigport pistons, head was shaved nothing extreme, TRD 0.8 headgasket

cam overlap isnt going to help when getting comp readings either


useing that "formula"from above, it ahs 10.98:1, beleivable, when it says multiply your engine size by 0.01, per cyc not over all