conpression on an rb20

[240love]

ok so im making this tread because i got a lil worried over a comment that carl H made to someone else asking something. On the other tread a guy asked what compression should be on a 20 because he was picking one up soon, Carl H said it sould be around 160 i think. Well when i tested my 20 my compression was way lower than that, not sure if i did it wrong but i doubt it. I got 120 all across except on #2 which was 115, the reason im worried about this is because well i just got the motor not so long ago, should i be worried? what shoul i do>?

[Bluefire]

Seems pretty damn low... but was the motor warmed up? If it was cold, it might give you low readings

[240love]

i tried both warm and cold and same results. Maybe the compression tester was broken or something idk, ill try a diffrent one later. Also my #2 isnt firing which is why im guessing it was lower than the rest. Man i hope i doesnt blow up or something cause it was so much work..lol

[Joe]

welp compression tests are strange animals

make sure you:have the throttle wide openremove all spark plugsdisable fuelhave the engine warmcrank the engine till the needle stops moving.

even on top of that, the variation between cylinders is more important than the number itself.

you are within 5 psi, thats pretty damn good. mine was 160-165 across all 6 when i pulled it. im a little worried its kinda low but try a different gauge and see what you get.

[Darius]

It does seem odd that they are all showing such even low numbers. I am with Kamin on redoing the test with a different gauge or making sure you follow the procedure he listed step by step. I wouldn't sweat it until you redid the test.

[seanman]

hmm, this thread is interesting cause i was emailing a jdm company about an rb20 and the guy said the compression test was 200 all the way across....now im reading this and seeing it should be about 160...does the 25 or 26 have 200psi?

[devil_child]

yeah wtf cuz the numbers written on my valvecover were from 13.5 bar to 14 i think. When I tested it myself cuz I was like WTF? it was around 200 per cylinder.....

[Bluefire]

The couple RB25 I tested ranged from 160-170... I figured the RB20 should have the same compression ratio, unless its higher...

[240love]

thanks for the advise guys and yes i will deffinetly try another tester. Ill post the results when i do

[Sky80]

Well to quote the FSM exactly:

RB26DETT/ RB20E DE DET/ CA18i/ RB25DE ENGINE

Compression gauge installation. Warm up the engine and remove all 6 sparkplugs.. Attach the adapter to the Allen compression gauge andset in a spark plug hole.

Compression pressure inspection' Depress the acceleration pedal fully. Turn the ignition switch to START position and crank the engine. Read compression pressure and the engine speed once the gauge needle stops moving.. When engine speed is out of specifications, check the specific gravity of the battery and perform test again if the battery is functioning properly.. lf the compression pressure is still not standard, inspect the components around the combustion chamber ( valves, valve seat, hydraulic valve lifters, piston rings, cylinde bore, cylinder head, cylinder head gasket etc.). Correct any malfunctions and repeat compression test.

It then further says the compression should be:RB26DETT should be 12.0 kg/cm^2 @ 300rpmand the RB20DET should be 12.0 kg/cm^2@ 300 rpm

and just incase you dont know what 12.0 kg/cm^2 is in PSI it is about 170.1 psi

[uber95]

For comparison, these were the readings from my RB20, they were in metric initially I converted.The cylinders read as follows in PSI#1-177.5~#2-177.5~#3-170.5~#4-177.5~#5-177.5 with #6 being the lowest at 163.5Carl mentioned that all cylinders should be within 5psi of each other, most people will shoot for no more than a 10% differential between highest reading and lowest. Anything between that deviation would be ok.

[Darius]

I would say those numbers look pretty good. Honestly though, it's not like you are going to want to rebuild just because your compression is a little low. I guess if you just received the motor or something and the compression wasn't what the supplier quoted, then there would be an issue.

I wouldn't sweat it, but if you're going to increase boost, make sure you tune it.