Weird values with compression test - 4AGE 16V

[eightsixboy]

Hi all,

Just did a comp test on two separate 4AG 16v red tops. One with 270k on it and with unknown history ie; don't know if it has a stock HG, rebuild or not etc, and the other one has 190k on it, big port cams, TRD 0.8mm HG, arp Headstuds.

Now, I did both tests on each car the same, back to back. Both warmed up to operating temp, unplugged fuel pump, both dry tests only.

The figures I got were as follows.

270km motor
1:230 2:230 3:210 4:230

TRD HG motor
1: 235 2: 235 :235 : 245

These figures are in PSI. The gauge set is from my work and is basically brand new, I have used it before about 2 years ago on a skyline I sold, didnt have any unusually high readings then, and afaik it hasn't been used much.

Do you think these figures are accurate at all?

I find it odd that both motors are

A) such high figures and more scary b) that both engines are so close in there figures.

What do you guys think?

[dnegative]

Gauge is up the shit for sure

[oldeskewltoy]

actually similar readings to be expected....

smallport originally came with smaller duration cams. smaller cams closer earlier and allows the engine to have more cranking compression



The ARP studs do nothing for compression... so you have one engine with a bit tighter gasket, but longer duration cams, the other a bit more gasket, but shorter duration cams.... that is why I said similar readings to be expected



As to their accuracy... and they numbers you have... stock unmodified "new" smallport would have 190psi... so not sure how you could add 30+psi without any mods......

[mattysshop]

Hey mate, i got around 220psi on a 'supercheap' brand (ie really cheap) multi use compression gauge (fuel pressure/boost pressure etc on the lower parts of the gauge) after i did the HG on that smallport and retorqued the ARP's.. i would expect that my gauge may be a little inaccurate.. compared to something that would be used at a proper workshop..

in addition to the .8mm MLS HG, it had a very light skim/machine.. for straightness, the machinist advised that it was 'pretty good' and didn't take much off at all.. and ofcourse the valve seats were recut.

also - i have checked them against eachother and i don't think there any different, but i did use the smallport cam gears on the bigport cams when i installed them..