Any suggestions or advice would be appreciated. I have a 1999 advantage 28 sport cat . I have a stock 500hp with a 250 mega blower 5psi no chiller.I just purchased a 420 mega and a chiller should I do anything to the heads or cam . also I have a xr drive with 1.5 gears.what would be safe boost I was thinking 7-10 psi . please any advice would be nice. I don't want to blow up motor. Motor has 200hrs

a good set of heads and the right cam with the 420 and chiller would make the boat a rocket but 5-6 lbs boost with the 420 with a stock hp500 won,t be a slouch by any means.

Do you think 7-10 is to much also what cam what heads

i think 7 would be my max on the stock engine.i,m no cam expert but a 525 efi cam or a crane 741 should do the job.with the addition of the heads&cam i think 9 lbs boost would be a safe number.we all love power but we also need to keep it safe.edit in,the afr 305 is a nice head.

What heads

I'll check them out thanks

I talked to co performance and they said there was no need to replace cam and heads they were good wouldn't make much difference in performance

Free advice from somebody on the phone??? You got what you paid for.

The carbed HP500 cam was never that good to start with on an NA engine. It s on a 110 lob sep and reverted water at idle. Not really a good blower cam either.

With 200 hrs on it, it needs at a minimum, new springs and a valve job and better head gaskets.

7-8lbs is the max I'd run.Your at 200hrs,time for springs in about 50-100hrs,so might as well freshen heads and get yourself either an hp500efi or crane 741 cam.this should get you an easy 700hp.

I'd go with the 525EFI cam, or the 168741. Very close in specs, but the 525 EFI cam is a 114 LSA , the 741 is a 112 LSA. Either one will be an improvement over the stock HP500 cam.

I would freshen the heads up at minimum, new springs to match new cams, valve jobs, head gaskets, etc. I'd keep the boost level to around 7lbs to start with, and go from there.

I think you are going to see some nice power gains. Theres a few who have upgraded their stock 575sci engines, (502 with 250/256 blower), with an 8-71 blower package from Dyers. The power gains were substantial, even without upping the boost. If you were say running the 250 blower at 5lbs non intercooled, and go to the 420 blower, intercooled at 6lbs, you'll be making quite a bit more power at wot..

6psi of cool air, will be much better than 5psi of hot air.