Griff

All you need to make 575hp out of an HP500 is a good head and cam combo.

powerquest208

Griff - I can put the 502 mag efi/mpi back on and make 575HP? Or convert my 502 to an 500HP = 575HP?

Young Performance

I'm here

You should be able to make approx. 550 using the 502 mag intake. The 500 efi intake is a better unit to start with, but you can use the 502 mag intake, although you will give up a little power. I would add some cubic inches if the bottom end needs to be freshened up. You can take it to a 516 or 524 very easily. This will still leave plenty room for future rebuilds. If you don't have to freshen the bottom end, then a cam change, increase in comp. ratio, some head and intake work, and programming will get you 525 - 550hp. If you do the bottom end and increase the inches, then you can make 550+hp.
On the other hand, if you change the intake to something like the Holley setup, then you can make 575+ with cast iron heads and well over 600hp with aluminum heads. I really like Holleys efi setup and use it often. It is a single plane intake with injector bosses casted into the intake, 2000 cfm throttle body, injectors, rails, etc. It runs around $2500 (without electronics) and is worth every penny. This will also be a great platform for future upgrades. I have made almost 800 hp with this setup on a 598.
Bottom line....you will be able to make more power if you go through the bottom end and increase the cubic inches. I still think we can get real close to your goal without doing that. It all depends on how much time is on the engine. Give me a shout if you have any more questions or if I can help in any way. Thanks.
Eddie

Here are a few pics of the Holley setup on a 540 with aluminum heads. This one made 701 hp.

Thunderstruck

John I sold all my 500 HP parts but we can discuss what to do. Look at your PM's.

Griff

If you carbed, you can make 575+HP with a good head and cam combo. Using the stock 502mpi injection will limit you as eddie said.

ThreeBears

I am curious about the electronics for the Holley EFI setup. Can the Merc box be reprogrammed, or do you need to change over to a MSD (or other) unit? Also, what about exhaust - at what point does the stock Merc exhaust become a limiting factor?

Young Performance

I only use the Mefi ecm on the engines that I build. That is why I buy the Holley setup without electronics. I don't think Holley's electronics are that good, especially in a boat. I use a Mefi 4 now, but have used a 1, 2 and 3 in the past. I use them because I think they are the best. They have the benefit of excellent knock protection.
As far as the exhaust, the stock setup becomes a restriction on any thing other than a stock engine. On some stock engines, they are already a restriction. I am referring to the stock manifolds. If you have a 500 or 525 with CMI's, then that is a different story.
Eddie

Advantage 27

I am going the route described by Eddie. I am turning a 509 into a 540 (melted a piston) and will be getting the Holley intake and using my MEFI4. I have to say that working with Eddie has been great and he is very meticulous about building a motor which will be rock solid. If your looking for a builder then he is the guy.
Shane

ThreeBears

OK ... this is going to be a real rookie question but ... MEFI = MSD or MEFI = Mercury?

Young Performance

Uh.....yes.

The Mefi (1,2 and 3) was used by Merc. for a long time.(10 years or more). Merc. never did use a Mefi 4. I think that Volvo and maybe Indmar or someone else may have used it, but Merc. never did. MSD does sell a Mefi 4. It is the same one that I use, except I do not get it from MSD. There are several versions of the Mefi 4. (4, 4A, 4B, 4C) Most people use the 4B.
Eddie