87 Shelby Z Pinging at 0+ PSI

87 Shelby Z - 2.2L
Forged Venolias
Ported head (unknown as to how much)
Mild cam. Has a very subtle tone at idle.
S60 turbo .63 a/r
+40 injectors.
11mm ARP Head studs.
Stage 4 BoostButton Cal. (Burned myself. Only the CEL flash option is enabled.)
Fuel pressure set at 55psi (after last increase) and base timing at 12 degrees.
Manual boost controller.

Was helping my friend get his car dialed in last night after redoing the vacuum line system and adding some proper instrumentation to the vehicle. We were slowly inching up the boost 1 or 2psi at a time and adding fuel pressure as needed. We started at 45psi and ended up at 55psi although it was a bit rich at that point. The car was doing awesome clear up to and including our last couple 15psi boost pulls. The wideband was reading fine, no CEL ping flash, just smooth all the way to redline. We figured it could do a little more and I dialed in another turn on the MBC. I started another 2nd-3rd-4th gear pull but as soon as the boost hit 16-17psi the engine stumbled hard for just a second then resumed running smooth again. We pulled to the side to inspect, nothing looked out of place so we limped it back without hitting boost because any time I'd give it throttle and the boost gauge would even think about creeping over 0psi, we were getting CEL flashing due to pinging. Everything looked fine after pulling it in the shop and the engine was still idling and free-revved smooth as ever.

After sleeping on it, I'm thinking we got some pinging on that last pull at 16-17psi and damaged the head gasket. What are all of your opinions on this assumption? I know I will need to do tests to verify, but it's currently the only idea I have. My friend is working today so I don't have access to the car.

Also, neither myself, nor my friend assembled the engine. He bought the car 80% completed where it just needed a bunch of little odds and ends and dialed in. I cannot attest to how the head was originally torqued down. Engine has very few miles on it as it was never running properly before he bought it

Assuming stock intercooler and pump gas as they are not mentioned in the list of modifications. I think you found the limitations of one or both of those.

What fuel was used?
What was the a/f ratio?

In my experience, the turbonator series of "tune" cal were too rich part throttle and too lean full throttle. They are good for a guide to help you start tuning. I would only ever turn up boost 2 psi at a time then check where the a/r ratio is before going higher with boost.

I'd never run them straight to full 17psi out the box, way too risky to trust a calibration.



NEVER tune with fuel pressure when you can just change the calibration instead! Matter of fact, you'd want a LOW as fuel pressure as you can get. Lower fuel pressure means your fuel pump can supply more fuel volume.

My bad. Spearco 1080 FMIC. Walboro 255 pump. 93 Octane pump gas.

A/F stayed between 10.1 and 10.5 all through the RPM range during our WOT pulls. Was 10.3 at the point of failure. Car was only hitting about 7-10psi max at part throttle with max a/f ratios at 13.

The Boost Button Stage 4 was doing great fuel wise. It was actually fine at 52psi on the fuel, and I had no intentions of setting it higher than stock pressure. It's been over 10 years since I've tuned one of these cars, so a small fuel pressure change was perfectly acceptable back then. It honestly felt like a "too much ignition advance = dead head gasket" stumble when it happened, but like I said, it's been a very long time since I've done one of these.
And no, I didn't just set the boost straight to 17psi, that would be insane. We started with the MBC at 8psi, dialed up the fuel pressure to stock levels which got the a/f in range, if not a bit rich, then we inches the boost up 1 to 2psi at a time. With a few pulls and some light cruising for cool down in between increases.
The main reason I started at 45psi of fuel and turned it up was because I couldn't find anywhere that said what psi to run with that calibration. At 52 it was fine, but we put it to 55 for a little insurance. If I did pop the head gasket, I'll have to go into the cal and pull some advance out at higher boost I'm guessing.