I thought it was the exhaust valve. I bought Fel-Pro Viton umbrella seals and the box says Exhaust Set. But sure as hell the seals are on the damn intake valves. Can't anything be straight forward with these cars? (1990 L98 IROC)

 

I've got them on both the exhaust and intake valves.

 

It's best to have them on both but they're usually only on the intake valves. When The intake valve is open the piston is on a down stroke drawing air/fuel into the cylinder. If the seal is worn out then it will also draw oil down the valve guide.

The exhaust valve seals only keep oil from leaking down into the cylinders when the engine is shut off.

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and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.69
Best MPH on a time slip: 121.52 altitude corrected to 127.76
Altitude corrected rear wheel HP based on power to weight ratio: 504.5
Best 60 foot: 1.546

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Almost right. I called the Fel-Pro tech line today and the umbrella seals are only meant for the exhaust valves. The intake valves get the hard clamp style like the originals (SS72527). If you use umbrella seals on the intake valves you pull in too much oil during operation.