HP500 boost question
 

I bought my boat back in July and has the HP500 motor with a weiand supercharger on it. From what I was told it was set at about 4psi of boost. What kind of boost can a stock hp500 handle without coming apart? The motor has 512 hours on it, and have no idea if it has ever been gone threw.

Do a compression or leak down test and that should tell you the condition of the heads. Regardless of those readings, I'd consider have the heads reworked over the winter.

Have one that is fresh with a procharger w/intercooler running 6psi

The blower shop has a handy effective compression ratio/fuel chart. 5psi @ 8.75:1 is in the 12:1 range if you're running 93 octane. Also has an equation to check the cfm requirements

Did a compression leak down test when I bought the boat in July and everything came out good. The boat runs awesome now, full tank of fuel with 5 people and it will run 74-74mph. Only problem is I just cant get the Rpm's up. Hangs around the 4900 mark, was wondering about adding a few pounds more boost before I started changing props around. Sounds kike 5-6psi is gonna be the max for the hp500 motors though.

What size weiand? If it's a 177 or a 256 I'd keep the boost around 4 with the 177 and 5 if a 256.

Full fuel and 5 people = a lot of weight 1500#'s or so???? Assuming you have a single engine that prob increasing the boat weight by 20-25%.
See what it runs with 1/4 tank and 1-2 peeps.

Wow, if I had an HP500 with 512 hours showing on it, and I did not know for sure that the valve springs had been changed out, I would make that the top of my winter project list. Especially with a supercharger. If it's completely stock, I'm guessing at the very least the head gaskets are not long for this world. Do yourself a favor and go through the top end of this motor over the winter so we won't have to read about you dropping a valve this spring and then having to go into scramble mode to get your boat back on the water for the season.

And no, I would not go over 5-6 lbs boost on an HP500, especially with high hours on the engine and drive. Good luck with it.

For the record, I believe HP500 valve springs are supposed to be changed around the 250 hour mark, so if this engine is virgin, you are at roughly twice the recommended maintenance interval.

I am going to go out on a limb and say this engine is not virgin, because 500 hrs on a 500 hp without a blower would be a miracle :D

I agree to at least do the top end before pushing it, but at 500 hrs the bottom should be looked at as well.

MT makes a good point on what blower you are running, follow his guide for boost.

IMO 4900 RPM is too low for that set up, I would be more comfortable at 5200 rpm, but more boost shouldn't be the only answer. Try some prop work, or a prop change. What prop and drive are you running now?

Also, install a boost gauge on your dash so you can see where you really are. They are great to have, and great for diagnostics on both the boost and vacuum side.