I dyno'd the car this Saturday and the rwhp and rwtq looked great until 5300 rpm and then it just laid over. Car made 408 rwtq peak and on it's way to the power peak for my 306 cam it just feel apart and laid over, only power peaking with 380 rwhp at 5200 rpm. I'm using the exact same heads/cam that I used on my 350 with the same CR ratio and I made 380 rwtq and 390 rwhp, and the rwhp peak was at 6300 rpm. When things break up at about 5200 rpm the curve just lays down and goes flat to 6200 then it starts to drop sharply.

I'm using my old valve springs which have about 3 years on them and 70k miles, yes I know it's likely the springs. However, I was wondering if anyone had any dyno runs online in which they found they had bad springs on their heads, causing slight valve float so I could compare?

Thanks,

 

Its most likely the springs. Even stock ones are really only good for about 80k.
However I would also check the MAF. A friend of mines car was doing that and he had over-oiled his K&N and oil got on the MAF. Just take it out and spray it with some contact cleaner if that is the case.

 

I'll take a look at the MAF, but I'm pretty sure it's fine according to the logs I pulled from LT1 Edit. AF ratio was 13:1 all the way across the board and the timing was perfect.

 

I'd put in a new timing chain if the one in there's been in awhile. Although your springs are probably the culprit.

 

How would a timming chain be a part of this issue?

i've got a summit double roller btw...

 

Valve train, springs have probably about had it, you know more about how much that car is been through and how strong its ran, eatin all those LS1s. Put new springs on that beast and you'll be good to go. Dont go over kill with the springs though.