This is a copy / paste from the corvette forums, (I figured I'd come ask the experts, LOL )

The car has 172k miles, and had a bottle in it before me getting it. zero knowledge of what type of kit though.

Car has long tubes, CAI/ LS6 intake, twin disc, NX wet 150 kit. (used TR6 plugs when nitrous was used)

SO here is where **** hits the fan... took the car to the track and went 11.8 at 124. The MPH was pretty unimpressive, so I figured there was something wrong. (considering the car went 117 before the long tubes and nitrous, with worse track conditions)

Well at the end of that run, The car refused to idle... also had to be push started with a car to get it to even crank back up. (had to get it to 20mph ish) no drop in power through the run, no backfires, no real issues... just didn't want to crank up on its own or idle. upon inspection, it pushed a lot of oil through the PCV system...

I decided to drive it home, It felt under powered around 1100 and under, but did not smoke, and took a 40 to 130 nitrous pull like a champ, but still refused to idle.
Pulled the plugs that night and they were BLACK HOLE black... I could see them swallowing the light around them they were so black, lol... Put new plugs in and it cranked up one time, and then never cranked up again that day. (left it alone after 5 tries)

So a week later after letting it sit in my shop, it started right up and idled fine.. It took it a few seconds on the starter to get it to finally kick over on its own, but it fired right up every time I tried after that first go....

Ran a basic compression test, got 120psi on all 8 cylinders +/- 1.5 lbs either way. That's a low number, but I'd call that a guage issue, and felt better about the consistency.

So heres where we get to the current status of the car... I pulled the heads and to my surprise, no scaring on the block at all ( thought I hurt a ring) and the head gaskets were good!...

So where I sit now is I have some LS9 Head gaskets on the way, and a set of cleaned up 317s sitting on the bench awaiting parts to come in.

Also have an LS9 cam and all the works to install it in the car...


HERE IS MY PROBLEM.... If you listen to half the story... You think rings, right? Well there's no way in hell I hurt 8 rings the exact same way... (refering to the PSI test being so even across all 8 cylinders)

The headgaskets were good...

And after letting it sit for a week, it starts right up..

WTF right!?!?!?!

Some guidance would be freaking great. If I need to just pull it out and go through it I will. I absolutely don't want to do that, because it's a pain in the ***... but Hell, It's already mostly apart...

But I'd love the "it doesn't sound like rings after I read the whole story" reply, lol.

 

Bump?

 

Hard to diagnose over the Internet, I agree 120 psi seems low but if they're all reading the same idk?

If it had nitrous at one point I want to assume the original owner had that tuned in? Have you looked at the tune lately?

It would be nice to hook it up to a scanner and see what's going on when it starts to stumble..

But too late now since you've disassembled it, just depends on what budget you have and if you have the downtime to pull the motor..

Me personally I would pull the motor with close to 200k, I know there's a lot of people that would just run it as is.. So it's just preference

 

I'm considering just pulling the engine out and going through it... It'd be cheaper now than later I guess. I am going for boost but I'm shooting for around 550-600whp, so I'm sure it's due for some maintenance..

BUT it's always hilarious to beat a ford guy and then let him know it has 170k plus miles on it!

 

Cam timing - push rods maybe bent valves?

 

It's a stock long block, I don't know how the cam timing would of got out of wack. The push rods looked good, and the valves weren't bent either. No marks on the pistons.

 

Does said car have a wideband?? If not is it possible you ran it lean and burnt the exhaust valves?

 

Leak down test will tell you if its cam timing or leaking past valves etc.

 

You're running rich on the nitrous. Probably too rich. That's why you fouled the plugs and it wouldn't idle. There's safe and then there's overkill.

Get the tune sorted before you start throwing money after anything else.

The compression test looks like crap tho. I would be worried that the rings are not sealing with the cylinders being washed with gas or something. Time to do a leakdown on it. The compression test should be 160 minimum and 180-200 ideally. But maybe it's the equipment as you said.

 

7mph from a 150shot tells me you had that thing fueled for a 300. Gave those pistons a bath and they didn't want to get out of the tub.

No reason for nitrous to push excess oil through the PCV, so even though everything 'looks' alright, something is definitely damaged. What? I don't know, but don't shortchange the obvious facts, it's hurt.

 

Not only do you wash cylinders with fuel, it dilutes the oil and wipes out the bearings as well!