This must have been covered before, but I couldn't find it...

I'm considering buying a boat with high hours, so the 502's will need rebuilding soon. What needs to be done to get to 500 HP, while retaining or improving reliability and drivability? I'm picking the 500 number mainly because I don't want to go the supercharger route, and having 1000 HP is a nice round number.

I don't have an unlimited budget, but I want to do it right, and not have to worry about it for awhile. I would gladly spend more $$ for higher quality parts than stock. Thanks in advance....

What year is it? I have a formula & a source for the necessary parts. Have to change the cam, lifters, inconel valves, modify ecm, and a couple other minor mods. I have 2 of the ecms for that exact conversion. Runs great when finished and you can't tell by looking at the engines that anything has been done. (sleeper)

Sounds perfect...the boat is a '96...

Very interesting. Mine is a '95. I've been thinkin of doing the same thing. Can the VST fuel system handle the flow? bj

CObarry

Been there, done that with a pair of 1996 Gen 5 502EFI's from Rod Dash @ Performance Marine in Oshkosh, Wi. I'm the kind of person that doesn't care to make those kind of mods in the garage or have just anyone do it for me. Reliability is the key for me as I frequently boat hundreds of miles away from home. I strongly recommend having someone do it that has a lot of experience in a particular build. My motors have been totally trouble free and have over 300 hrs with 500HP. I did a top end overhaul @ 250 hrs on Rods recommendation. I did springs, retainers and lifters. The mods listed after your initial post are pretty much exactly what I had done by Rod. He knows the formula and is a straight up guy. He had me add long, through transom risers that water at the very end of the pipes to ward off any possible thoughts of reversion. I use Stainless Marine exhaust. My Crane cams are reasonably aggressive and the whole setup is absolutely turn-key and runs exceptionally well. I believe the two most important factors are experience and dyno building. Done as Rod did mine, you will see a substantial boost in performance and still retain the 502EFI's great reliability. And yes, the stock VST system will support 500HP, but not too much more. That according to Rod.

If you're considering changing out internals anyway, why not make it a 540 while you're at it. It coulde still look stock as it does now.

We have done several of these upgrades so I listed all the parts and the machine work and the Labor on my Website www.crockettmarineengines.com. We also remove the VST tank and add a new fuel pump and fuel cooler.

Expert advise from some experts here on OSO. Use a shop like these who know performance marine engines and you will always be a "happy camper" with your 500HP+ 502's.
Ray @ Raylar

CObarry
VERY DO ABLE 97 31 SS SONIC TWIN 502EFI WITH VST FUEL PUMPS RAN 68MPH GPS @8700LBS TURNING STOCK 26 BRAVO 1'S TOO 4900 - 5000 RPM : AFTER 500 HP UP GRADE TURNING LABBED 30" BRAVO 1'S @ 4900-5000 RPM 77-78MPH @ 8700LBS(RAN 80MPH @5200 RPM IN POKER RUN FORM LAST YEAR WITH 4 BIG GUYS ON BORED) .CHANGES ARE : FUEL REG., CP'S HIGH VOLUME MECH. GEN 5/6 FUEL PUMP, STOCK VST PUMP, WITH MILD HEAD WORK AND SOME CUSTOM STICKS, Tyler Crockett DID THE ECM REPROGRAMMING DID A GREAT JOB!!. CAN YOU SAY SLEEPER !!!COST UNDER $7000 FOR FULL REBUILD DONE WITH THIS PRICE. 300 PLUS HOURS @ TIME OF REBUILD.RUNS IDLES DOCKS BETTER THAN EVER BEFORE!

call 816 380 4732 travis has new springs cam for hp500, dump the iron log manafolds, water pump. trick up the computer should make 510 hp