Mile High Perf Dyno Tune 340

Well, work and business trips have delayed further testing and investigation of why the engine isn't performing as expected. Did a compression test and had varying results. ~120 PSI in most cylinders, but down to 107 in others. With 11.9 PSI atmospheric pressure at 6000 feet, probably not bad. But I needed to know why the low pressure in #7. So.....

I built a leak down tester (~$30 in parts from hardware store, I can provide details or build you one if desired). Using 80 PSI feed pressure, most cylinders had 79 PSI after the orifice restriction. Not bad. But #7 was 72. Oops, leak. Sound of air from exhaust port confirmed it was a leaking exhaust valve.

So.... I pulled the head. With tti exhaust, I wanted to not pull the headers. On the drivers side, if you remove the steering column, you can move the header enough to get to the head bolts w/o the hastle of removing the header completely.

Once off the engine, I put solvent in the exhaust ports and found leakage around the valve seats of several valves. Disapointed as I had a 3 angle valve job done (years ago when I lived in CA). I took the heads to Colorado Custom Heads in Englewood. They will inspect and report back. I will post what is found.

I inspected the FelPro head gaskets and found no evidence of leakage. I want to increase compression ratio to compensate for the high altitude, so I am considering 0.020" thick head gaskets. Mancini has several to choose from at 0.024" compressed thickness. Any suggestions from FABO memebers?

I also noticed that the bottom of the intake manifold gasket may not have been compressed against the head. The manifod is an older Edelbrock Performer. Small intake ports compared to my gasket matched 340 heads. I am seriously considering an RPM Air Gap to replace the old one. Thoughts?

With all these issues with the engine, I am surprised that the dyno showed 330 HP. Colorado Custom Heads said I should pick up 10 more HP with good compression in all cylinders. That would be great, especially if I get the low-mid range perforamnce back. I also want to see the vacuum increase from 6" when I took the heads off to something like 9-11". I do hope that the manifold leak was the cause of this, but I coulldn't determin if the gasket was really leaking or just looked like it was not compressed. I did seal the gasket to the manifold with Copper Coat to be sure it didn't move during instillation, and it didn't move. It came off the head cleanly.

Any other thoughts on this would be appreciated.

Bob