Car: Built GSR bottom end, GSR head with ITR valves, springs, and cams. Tuned to 25psi/ 500hp.

Event: Boost solenoid tuning, Overboosted and spun. I believe I hit the rpm and boost spark cuts at 8525rpm and 28psi at the same time according to the datalog. The result was a huge backfire and my exhaust actually seperated at the slip joint. LOL

Immediently parked in a near by parking lot. Was able to get the exhaust together and drove it home. Engine ran very rough, sounded like a WRX.

Diagnosis: Compression test showed good compression in Cyl 1-3 (180psi) but Cyl 4 had 0psi. Looked at the piston with a borescope and top of the piston looked great. Removed valve cover to inspect the valve train. No missing retainer clips or dropped valves. Inspected valve movement while cranking engine by hand and all 4 valves seem to have full movement. Inspected valve lash and found one of the exhaust valves had NO clearance. The adjuster lock nut was NOT loose. I adjusted the clearance back to .007" and reinspected the other 3 which were fine. Ran the compression test again and compression went up to 90psi this time.

I suspect something impacted the valve smashing the clearance. I am surprised the other exhaust valve is fine and the "bad" valve doesnt stick when moving up/down. Does everyone agree this sounds like a bent valve?

 

you can try this and use the compression tool hook to a compressor and blow air thru the spark plug hole

but b4 you do that make sure that cylinder is at tdc (compression stroke) and remove the pcv hose both sides plug 1 with a bolt

blow air into cyl and if air comes out the exhaust then yea your valve is bent if the int manifold its your intake valves if thru 1 of the pcv hoses then its your rings