I just did a compression test today on my stock bottom end. 178, 178, 180, 178. Is this acceptable to turbo?

im pretty sure that the compression should be 180-220 you are pretty close. I read some where that if it goes below 150 you will need a rebuild or servised.

the stock gs-t, gs-x, have a compression ratio of 8.5. since you have 8.5 pistons i believe you should basically have the same compression pressure. the standard is 178 psi, bottom limit is 133 psi, and pressure difference of all cylinders is 14 psi. i got info strait from my factory serice manual. hope it helps

I 8.5:1 cr pistons aren't installed yet. I still have stock bottom end, stock compression.

Those are great numbers! Happy boosting ;)

Those numbers arent bad, but not very high either, but I'd say its ready for boost. On my stock bottom end, with 70,000+ miles, i got 200-205 compression accross. Just be aware that a rebuild will be needed before too long, esp if you run higher boost. It should still last you quite some time though, assuming proper fueling and tuning, of course.

Just wondering because I was spraying nitrous awhile back. Just a 50 shot. Better safe then sorry.

Xtreme, how hard were you on the car that you broke a piston?

>Just wondering because I was spraying nitrous awhile back.
>Just a 50 shot. Better safe then sorry.
>
>Xtreme, how hard were you on the car that you broke a
>piston?


Well i was running 10 psi. Its kind of hard to say exactly what did it, but my guess is detonation. Running that high of boost on stock internals is def pushing them to the limits, but that, with some detonation, is what most likely broke 2 piston ring landings off of the piston. Overall, what caused the detonation? Again, my best guess is this. I was part throttle boosting, not WOT, the ECU was still in closed loop, hit 10 psi, then i heard that nasty metlic rattling (detonation). When in closed loop, the ecu advaces timing quite a bit, and that along with that much boost pressure, caused detonation. But, this is only a good guess. All in all, rule out detonation, I still think our stock internals can handle 10 psi of boost. It just cant handle the extreme cylinder pressures caused by detonation at 10 psi of boost. Factors that can help detonation occur: higher boost pressures, spark timing, and high coolant temps. I may have done the damage when i was tuning my boost controller. I once spiked to about 13 psi on the boost gauge, i heard detonation then too, so that may have done it, cant say for sure. Luckily, I was able to transplant one of Matt_95tgs's old pistons into my block in a day, to get her back up and running until the winter.

Your numbers are fine. You'll probably end up damaging the pistons eventually anyway (you'll get boost happy, we all do) and then rebuilding, so who cares what the compression on the stock bottom end is like? As long as it's even and the numbers are close, i wouldn't give it a second thought.

Thanks Dino. You're always confidence inspiring!

As for the detonation part. What if I bought an MSD to pull timing at a preset boost level. A while back I read that Wyatt said to retard 1-1.5 degrees of timing for every pound of boost after 5 psi. Will this help at all if running 10 psi every once and a while?