Just wanted everyone's opinion- have a loss of power over about 5K and the only major thing I have changed is the heads. I have KB 12cc dish HyperTec. pistons, which should put my current comp. at 9.7:1. I went from L98 aluminum heads to Pro-Comp 220cc heads(58cc to 64cc) and kept everything else the same. I have gone through almost anything you can think of to solve the problem. I have changed to a Mallory Pro Comp 110 pump, Mallory return regulator (which was suggested on this site and works great), jetted up, up some more and back down, advanced and retarded timing, changed plugs, wires, cap, rotor, and coil. I have checked fuel pressure and all the way through the run it never falters from 6psi. The car has no ***** after around 5K and struggles to 6K where it used to rev with no problem with the old heads.

My question is: my machine shop talked me out of AFR 195's to go with the Pro Comp 220's(let the flaming begin) and I am wondering if this is just too much intake runner/drop in compression for my setup with such an aggressive cam (no dynamic compression). The cam has 241/249 dur. @ 0.050". A friend has given me a Victor Jr. to try in place of my Edelbrock RPM in the meantime.

Thanks

 

It dropped your compression, which is a power loss in itself. The heads also flow way to much for that engine. The 195 cc's would have been a lot better for it. If you had higher compression you would have an easier time tuning to the 220's.

 

Since you say your loss in power occurs only over 5k or so, it's not an issue of the head ports being too big. That problem would show up more at the lower revs.
It sounds to me like your valvesprings are too weak or not set up right, and the valves are floating above 5k.

 

I agree, check the valve spring pressure.

 

Bingo. That's the punchline right there.

Valve springs are a great thing to check first, I didn't even think of that. Start there, then perhaps look at spark or something. But since you replaced the heads, the valve springs on the heads are an excellent culprit and would make the most sense.

 

Thanks for the input, I called Lunati today and they told me the exact same thing-sounds like a spring problem. I swapped the beehive springs that came with the cam to the new heads, but I'll double check them. Lunati tech said a valve or valves might be too tight and recommended setting the lash @ 1/4 turn instead of 1/2 turn.

 

Did you check the installed height of the springs when you installed them? Aftermarket heads can often use longer valves and/or deeper spring pockets than stock which can open up your spring's installed height and reduce spring pressure at all points in the lift curve. Having the matching springs for your cam is good, but you also have to make sure they are at the specified installed height when you install them.

High RPM power drop-off usually falls into a few general categories. Valve springs being one of them, obviously. The others are inadequate fuel supply (which you already ruled out), inadequate or improperly timed spark (which seems unlikely in this case), or a restriction of the intake or exhaust system (for example: is your carb getting to full WOT when you mash the pedal? If you're running a cat, is it possible it's getting plugged up or internally collapsed?)

 

I had my machine shop set up the springs according to the cam card from Lunati so heights/pressures would be correct. I have true dual exhaust with hedman longtubes 2 & 1/2" pipes to 2 Flowmaster 40 series mufflers and have had a friend push the pedal to the floor to check for WOT on the carb.

I will look for broken springs, double check the valve adjustment and loosen them up a little and see what effect that has.

Thanks for all ideas, I'm overlooking something and need fresh thoughts.

 

IMHO you have multiple problems. Compression is to low for the bigger ports. The ports are to big. The cam is to big for the combination. Possible valve spring problems.

 

Just a follow-up, looks like the valve train was the problem. I adjusted the valves and adjusted them too tight by about 1/2 to 3/4 turn. Somehow I didn't wipe a lobe and now it pulls great to redline. After I readjust jetting and timing I should be ready to try it at the track. Thanks for the help, valvetrain/springs were right on the money.