598 bbc na motor lost rpm
 

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?

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

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.

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.

What brand springs, how many hours are on them?

comp 959 about 75 hrs

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

I will check them tomorrow

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