What'd I do to my engine? (bang!)

[zlexiss]

Car is a 2001 5-speed Firebird. Build has about 100 miles on it, pretty much the works - Started with a Series 3 block from a FWD with about 18k on it, added Abbott Racing Stage 3 heads, ARH road racing cam, ARH ported intakes, double roller kit incl. zzp milled oil pump cover, pacesetter headers, 30% upsized injectors, and more..

Was doing wideband tuning (FAST unit through EIO). Fuel was tracking commands pretty well, still some nagging knock I hadn't gotten to yet on WOT but cruising well. Just coasting down in prob 4th gear, 2400 rpm foot off the gas, when bang! rattle rattle rattle (metal noise). Pulled over and killed the engine. See the attached jpg for logging info:

Frame ~615 end last WOT run
Frames 620-640 2 upshifts
Frames 675 car goes DFCO lean as my foot is off the gas
Frame 700 something just went wrong
Frame 725 drop to neutral, bump the gas a couple times (not best idea, but I'm new to the engine metal clanging noise thing)

What's to see? Manifold vacuum gone at idle. About 80-90 versus 50 at the start of the run. Airflow is ~25% lower after as well (less vacuum to pull through the closed throttle plate).
So I figure I broke something in the valve train, prob intake side, causing gas to get back into the intake.
Pulled both valve covers - nothing out of the ordinary
Pulled all 6 plugs - no visible mashing or damage

Before I take more stuff apart, looking for some good educated guesses. What's making the noise and where did my intake manifold vacuum go?

[WarShrike]

Re: What'd I do to my engine? (bang!)

Kinda hard to tell with how small the image is. Looks like you had a lot of KR there.

What does the oil look like?

Some people eliminate DFCO so you don't get lean spikes between shifts.

[ssms5411]

Re: What'd I do to my engine? (bang!)

Can't tell from the image, its too small for me to read. Are you using a wideband or narrow band for A/F ratio?From your post looks like narrow which is a mistake for tuning, you should use a wideband when tuning. What was the timing set at? How much KR at WOT?

[zlexiss]

Re: What'd I do to my engine? (bang!)

Sorry forum limits on image size, let me see if I can post an IMG link somewhere. AFR is with a FAST wideband kit. Too bad forum here won't let me upload tune and log files, I can email them if you pm me an address.

[zlexiss]

Re: What'd I do to my engine? (bang!)

[ssms5411]

Re: What'd I do to my engine? (bang!)

Sent you a PM.

[bigbrian442]

Re: What'd I do to my engine? (bang!)

Have you done a compression test?

[ssms5411]

Re: What'd I do to my engine? (bang!)

Sent you a email back to you, forgot to ask what valve springs did you use?

[Hib Halverson]

My guess, based on your post and that you had detonation, you saw nothing out of the ordinary when you had the rocker covers off, the engine still runs but rattles, you now have less manifold vac. and you have less airflow is you broke a piston. I'll be interested to read what you find when you tear the motor down.