Found out today that i probley tuliped a valve, and need to pull the heads. What up grades do i want to do? I would like more power with out a blower, so what should i do? ANY SUGGESTIONS WOULD BE APPRECIATED. I would like to make 500 hp if possible. I have stainless marine headers, and vortec flame arrestor. Will porting and polishing, rollar rockers, and my be a cam change get me where i want to be. What cam would i use, i don't want reversion problems. thanks guys!

Installing larger intake valves and doing a little grinding in the valve pockets (just below the valve seats) will help if you install a little better camshaft.

The stock camshaft can be replaced with an aftermarket camshaft that opens and closes the valves a little faster. If you keep the same duration numbers as stock (224/224 intake/exhaust duration) but tighten the lobe separation angle to 112 and retard the camshaft to 110 intake lobe centerline, the computer will NOT need to be reprogrammed.

Adding about 6 degrees more exhaust duration would also help performance and not hurt the ECM calibration (224/230 intake/exhaust duration).

Choosing an aftermarket camshaft that has less than .550 inches of valve lift, will allow you to retain the stock valve springs, stock roller lifters and stock non adjustable rocker arms.

Comp Cams can custom grind a camshaft with these specs for a little extra money. The Comp Cams XR 276HR, custom ground with a 112 LSA and a 110 Intake Centerline, would be a great camshaft for your MPI engine.

Sincerely
Dennis Moore

thanks dennis i will order the custom cut cam, how much hp do you think i will net with the upgrades? By adding the cam roller rockers and head job can i expect 75 to 100 increase or is that unrealistic?

I would think that you will pick up a solid 25 horsepower.

According to an article in Hot Boat Magazine a couple years ago, Tyler Crockett did some upgrades to a 502MPI. He also cut the heads .020" to get the compression up a little. Going by my memory, he also, installed larger valves, added roller rocker arms, installed a slightly larger cam something like what Dennis Moore has suggested, K&N air filter, aftermarket exhaust and reprogramed the ECU. According to Tyler Crocket's dyno test they saw roughly a 100hp gain with those mods.