dennis r

iTrader: (1)

I have a 598 bbc na it dynoed at 830 hp. Last year my last run of the year I mad a pass with it and it went 105 @6300 rpm. I turned around and tried to back it up and I could only get about 5600 rpm out of it. I have looked at everything I can think of any suggestions?

BenPerfected

Two thoughts, leak down test and valve spring pressure check. We used to do both these test and reset the lash after every race.

dennis r

iTrader: (1)

I did a leak down on it and it looked good.I redid the valve lash. I was thinking the valve pressure but I thought it would start popping if I had a bad spring.

BenPerfected

I don't think a broken spring will necessarily cause a pop in all cases. If you break an inter spring, you can just lose performance....maybe like a valve float. I not an expert and we never broke a spring. Between these two test, you learn a lot about the health of your engine. The Moroso spring tester is only about $100...Jegs or Summit. The biggest hassel is your exhaust manifolds may be in the way. The LSM spring tester may be more user friendly on a fully dressed marine engine.
Based on back to back WOT runs, this is a good place to look for an issue.

GPM

What brand springs, how many hours are on them?

dennis r

iTrader: (1)

comp 959 about 75 hrs

GPM

I may be wrong, but I would bet they are shot.

dennis r

iTrader: (1)

I will check them tomorrow

Young Performance

I'm agreeing with Ben.....I would say a broken spring or two. If the inner only is broken, it probably will not have a miss or pop. It will just not pull as high since it is going into valve float. Check them out. I think you will find the problem.
If the springs are good, then check for a cam lobe going away. The easiest thing to do is to put a dial indicator on the retainer and roll the engine over. Just like the springs, it will be pretty obvious as to which one is bad.
Eddie