Truck had miles on it and the boost was at 12lbs at the time. The extra pressure pushes the exhaust valve closed with the inherient overall between intake and exhaust. At least that what the machine shop said when he replaced al the exhaust valve guides.

 

Can I assume you had some hard driving or was this normal driving?

 

I'm not the easiest driver, but it is my daily driver, I do tow with it occasionally and it never went to the drag strip. But I did have a lot of boost running through it. L's only had 8lbs and I was at 12lbs when I had a problem. The NA motors should be able to go 200,000miles. I put the blower on at 90,000miles and rebuilt at 120,000miles. Saw raw oil coming out of exhaust. Rings showed signs of wear as well. And I was itching to rebuild the motor to include forged crank, rods and pistons as well! If you keep the boost at or below 10lbs and drive like you own it, you should be OK.