Have a friend that is considering some mods to a 502 mag. I have had some nice 454 carb packages and had a couple of blower motors, but am a bit stymied as to the best combo in this case. The most minimal case would be that he keep the displacement the same and just freshen up what he has, even keeping the stock rec-port heads. Unless I am missing something, the only obvious mods are cam choice, induction and exhaust improvements. Since this is already an injected motor, what can be done to this to complement a more aggressive cam (gen VI motor)? I feel relatively comfortable if we ripped the injection off and went with a carb, but this seems like a waste with this relatively mild setup. I would hope that we could easily gain 100hp at the prop without sacrificing too much driveability. I have heard that the stock injection setup is right at the end of it's potiential. Is this really true?

The other possibility is to bore and stroke it to 540ci, if the budget allows. I guess I need expert advice about the stock mpi setup and modifications that can be made.....

Arizona speed and marine did some major mods to some 502's and it was published in Hot Boat magazine a few years ago. Call them up or search HotBoat back issues, Good Luck The Ironman.

Brad-
100HP from that set-up is a taller order than one might think, as the manifold/plenum were designed with a specific power output in mind, and as power increases [modifications] are made, this long runner/dry flow setup becomes comprimised in its ability to perform as intended. In a speed density type system, you must give the MAP sensor a signal it can read, this means the engine must maintain decent vacuum at idle and part throttle, which then means high overlap cams are out, unless you dont care about having a dirty, unstable idle and crappy low RPM performance....kind of negates the whole reason why we enjoy EFI motors. In laymans terms, that long runner manifold kind of works like a header in reverse, and when intake reversion is introduced with a higher overlap cam, these pulses are exemplfied [more so than with short runners], spoiling the clean air supply in the plenum. With all this in mind, here are some things you can do within the budget of a mere mortal[with the stock heads] Go with a higher lift cam while keeping close to the original 225 @.050 on the intake, take the exhaust duration out a LITTLE further, somewhere around 230 [Remember, you are trying to keep overlap to a minimum] 114 LSA with 112 intake centerline. I know from my own experience a cam with these specs works well in the setup you have. You can mill the heads for a little boost in compression, and maybe a bowl port. After this is done, get an adjustable fuel pressure regulator as you will probably need to bump the fuel pressure just a little bit. If you are propped so that you are bumping the rev-limiter, send your MEFI out to get the rev limit raised and maybe a little less conservitve advance. Someone will have to prove to me that messing with the fuel tables does much. I think you would be pleased with the imprvements with this low budget upgrade, but its not going to be 100HP, maybe 65? The higher lift cam with faster ramps will give you a more powerful engine across the entire RPM range. If you want more goe with the carb and cam. If you want even more, keep your set up and add a well engineered supercharger setup...it will work very well with your current setup. BTW- I am a hobbyist not an expert....but the money I've spent on this type of induction has made me form some strong opinions...if you total allthe HP gains from the products some of these people sell, you could have SC900 power in no time, lets see.... Good Luck

Brad;

The bottom end of a 502 is strong as hell and I don't believe you'll see enough of a gain by going to a 540 to justify the expense. I don't know a ton about the EFI side of things, but from my experience on the other side 100 hp should be no problem if you change the following; do some port work on the heads, 3 angle valve job etc, cam change, intake and carb. My previous 502 had stock heads fully ported, solid roller cam 252/258 @.050 .680/.708 lift on 114 centerline, dart intake, and 1050 Dominator (which was too big) 850 would be best. This motor made every bit of 600 hp @5500 rpms. Do some checking to see if EFI could support this, but I know the above combination will pick you up over 100 hp (more like 150) What kind of exhaust are you running?

It's a friend's that would like to go faster. I agree totally from the carb standpoint, I've done it before. I just didn't know where to go with the EFI questions. If it were mine, I would probably just rip it off, but it would be nice if it could support these mods and give added tractability. Thanks all for the advice, I will give AZ speed a call.

I completely agree regarding the 502 guts, that's why I would rather see my friend go this route for his first custom. It doesn't make sense to throw all those parts away for his first motor.

BTW, that sounds like exactly the cam in my blower motor! Who made that cam for you?

I originally bought that cam from Nickerson and sold it to jdnca1. Dean sold it to me with the thought that I may want to go the blower route. I chose to go with a high compression naturally aspirated motor instead of going blower. My motor was a 454 and the cylinder pressures were quite low with that cam. It turned out to be a pretty decent cam for his 502. It had a choppy sounding idle, but the vacuum signal was very strong. I don't know who Dean has grind the cams he uses. As for the 502 EFI I recall Tyler Crockett writing an article in Hot Boat about a motor that they modified. They had very good results with the existing EFI unit. I can't remember the issue but it went in a 26 Velocity.

Brad,
A friend of mine has just what you need for sale !
Dart heads (stock) , I don't remember which model , I can find out
Brodix intake
Solid roller cam , .680 lift, .258/ .254 @.050 on a 112 c/l
Isky Lifters
Braswell 1050 dominator,
I'm not quite sure about the specks on the cam , I'm going from memory (and it's not that good) I think he want's $3000.00 for everything.

That combination on a 8.5:1 CR 540 is pushing a non stepped 27 Fountain 82mph, so it' got to be in the 600's .
If your interested PM me and I will get you his phone number.

Check the stern drive tech in the October 2000 Hot Boat. They gained 100 HP on a 502 mag EFI by doing head work, cam, exhaust, and reprogramming the ecu. They boat was a 28 Velocity and they retained the stock intake and look. Looks like a nice first custom project.

Wette Vette, that is the same cam I am using in my blown 540. Predetor cams in some small Penn town made it. It only made 120lbs cranking pressure in that motor. Made peak power at 6000rpm.

'26, I'll pass that on to my friend.

I need to subscribe to Hot Boat