Just did my first compression test woo. Car hadn't been started in a month or so, but jumped it and ran it in for a good 15 mins or so. So my results were: 210, 200, 210, 210, 205, 210... Is this right? The compression tester has been used previously and proven to be relatively accurate (checked against RACV tester). Isn't NA meant to be about 180 or something?
they're good results (not much variation between cylinders), i think mine were roughly 190-200. you can use this as a good selling point when you pull out the NA engine.
give me your motor. sandeep's car got 190-200 average across all cylinders which im already jealous of. i'm only on a lazy 175 across all, now i wish i had a bit more...
ahh excellent I was worried because everywhere i've read it says 180 is a very good result (not saying it isn't by the way). Maybe I should take her to the dyno and see what figures I can pull? Very pleased though. Also Kirill said my car pulled fairly well (went from NA 2 seater to a TT) though i'm sure he can make comment when he comes online later.
So what is a factory quoted value for compression on an NA? I've been unable to find a suitable answer, everywhere I see, 180 is quoted but this cannot be for an NA, surely, when several of us are nudging over 200?? edit: sorry for the epic sentence
So 186 is straight off the showroom floor...Why are some of us getting 200 plus? Is this due to skimming of the heads raising compression, thinner head gasket? I'm just interested to know, people are getting 180 and they have a almost new 300zx and we're running 200-210 and don't know what's going on
I dont beleive those results.... 186 is factory compression, with most NA zeds these days sitting somewhere in the 160-175 psi range. I dont know if excess carbon buildup could increase the comp ratio, but I would be dubious about compression figures above the factory specs. I suspect that the gauge may be a little out. Either way, as long as the compression is consistent among the cylinders, thats the main thing.
I'm also dubious but I used the same gauge (kbro/kirills gauge at least) which is the same as forum member Martins who got 180 across the board. It has also proved consistent on another vehicle (non 300zx) as compared to a test done by RACV. It also gave kirill his recent TT figures, which (if it really WAS out by 30 psi) would mean his results were shocking. Having just had a spin in his car i very much doubt his engine is in that bad condition. I dunno, it's all very confusing.
Kiril is coming over here for a boost leak test Tuesday. Tell him to bring his compression tester and we can try it against my expensive one.
i'll PM him I would like to know for sure if it is accurate as that's all I want, a true indication of how healthy my engine is.
If i remember correctly my readings were between 200-220psi. Also tried 2 different gauges both results were within a couple psi of each other. James
Hmm, very interesting to see that a few members have gotten 200+ on their NAs. As for the boost gauge tester, we did everything as stated, and Evan's was the third car I did. (Previous cars were my TT and a mate's s14, my results matched the results RACV achieved on his car). I guess i'll just take it to Graham's and test it against his uber-one. (As Evan mentioned though, my comp tester is the exact one used by member martin on his NA, he achieved 186+ across the board) I will post up results on Tuesday as to whether my comp tester is accurate or not. If it severely overreads, that means i'm in trouble, as my comp of 130-140 will now become 100-110 -Kirill
i did a compression test on my old engine and all were around 240. but i can explain the difference i reackon. when i did mine it was cold and i had all the plugs out and most of all i had the car on our rather expensive charger jump starter, on the jump start mode(it can jump start dad's 15L trucks),which can make the starter motor spin much much faster because its got 14.4 v instead of the probly something like 11.59v you would have in a normal battery and with the charger id have unlimited(virtualy) amps.
But that doesn't explain my difference. Mine was done on a recently jump started battery and then a 15-20 minute hard run in, so it was quite hot when we did the test. You're meant to take all the spark plugs out for the test anyway so that doesn't explain it. And if you're cranking with more volts than necessary that shouldn't change anything either, it can old pressurise to a certain point, otherwise you could keep cranking forever and get more and more compression.
yeah but the faster you do it the less pressure escapes past the ring ect. but my gauge could be off.but i don't think it would be the way off
other wise the only way i can see an increase of compresion would be due to oil in the chamber or/and a carbon build up in the chamber
