502 MPI Headwork and camshaft = how much hp?
 

Okay, my eyes are tired from reading all the camshaft and headwork posts I could find!

Dennis Moore and JimV seem to have the answers but anyone else feel free to jump in here.

I have a 1995 502 MPI completely stock and like all of us I want more power and speed.

How much horsepower can be gained from having my stock heads worked and a camshaft change while leaving the ECU alone? Will I have to go to aftermarket exhaust? I want to keep RPM's under 5200 because I run wide open for long peiods of time and I want to be able to run silent choice at idle(if that is possible).

What kind of realistic hp gains can be obtained?

The intake will limit your horsepower increases.

From what I have read on the board the MPI system is good to about 600 hp. Which I am sure I won't be close to with just headwork and a cam(and maybe exhaust).

Has anyone ever had the intake redone by Extrude hone. If I am saying it correct? It's where they squeeze a compressed abrasive through it acting like a polisher. I know lots of guys with mustangs do it to their intakes to flow air better

502 efi upgrades
 

black hawk az speed and marine has something called "short runner manifolds" they have an exchange program where you send in your stock intake manifold and they send you one already machined out . i have gone through this 502 efi upgrade thing over and over and decided for the $$ and performance you can't beat the super chargers !! i decided on the pro charger m3 running 3psi boost 89 octane fuel and get at least 580hp!! can't beat it for perf. and reliability!!

The intake runners on the 502 EFI are huge for an engine running at only 5,200 rpm. It almost seems silly to suggest making them larger. The engine can only pull in as much of an air/fuel mixture as the intake valves and the intake camshaft lobes will allow. The camshaft is the restriction to the air/fuel mixture moving into the cylinders on this engine.

You can increase your power considerably by changing the camshaft to one that opens and closes the valves faster. Keep with the same intake duration specs at .050 (as the stock camshaft) but with a faster opening and closing rate. Add about 6 degrees more exhaust duration. Tighten up the lobe separation angle to 110.

I suggest the Comp Cams Xtreme Energy XE 268H it has 224/230 intake/exhaust duration, .515/.520 intake/exhaust lift and a 110 LSA. It will work with the stock MEFI program, the stock valve springs and not require adjustable rocker arms.

It will give you an excellent performance increase (25-35 horsepower).

If you feel you need head work, increase the intake valve diameter and concentrate all of the work into the area where the air/fuel mixture passes the intake valve and enters the cylinder (the valve bowls and seats). This area is the only restriction to air/fuel mixture flow in a low rpm big block with rectangle port heads.
Sincerely
Dennis Moore

Dennis, thanks for the reply. If I have my heads done I will definitely have JimV do them. If I do the heads and camshaft what kind of hp increase could I see? What if I switched exhaust too?

Also, I remember in a couple of threads you suggested the Edelbrock 5062 which has .527 intake and .553 exhaust lift. Would this give me a little more power or seeing that it is a 114 LSA would it be about the same as the Comp Cam?

26Sonic and BUDAH, I have seriously considered a whipple and running it at low boost to save the drive. But, there is one small problem, it's way to easy to increase boost and hp! I know that I will want more after a short period of time and if it's that easy I'll do it! :D

BUDAH, I am not concerned with holeshots because I baby it now. What I am concerned with is getting air under my props at high speed which can be east to do in sloppy water with the blackhawk drive since it is so short. Another problem is prop choices for my drive. I would probably have to regear to a 1.36 which would be even more $$$. Believe me, I would love to do it, I just don't have the $$$ for all of it!

I guess what I was looking for is a little more hp and a few mph while keeping my gearing and the drive fairly safe.

A modified 502 Mag MPI needs better exhaust to perform. So add another $2K to the budget and get something that flows better than the stock manifolds.

Ron

Budah
I would think the camshaft would be good for a 2 or 3 MPH increase if he reprops the boat. The head work wouldn't make any more horsepower, but he could brag about the expensive heads on his boat! If he changes the exhaust he will have to reprogram the ECM or (at the least) increase the fuel pressure.
Sincerely
Dennis Moore

Thanks Dennis, headwork won't do any good? I take it they flow good enough until you get into higher hp and higher rpm?

What about a more aggressive cam with springs and adjustable rockers and reprogramming the ECM?

If you are going to reprogram the ECM then you should improve the exhaust and install a roller camshaft. Contact Arizona Speed and Marine and ask them what camshaft and exhaust they recommend for their computer upgrade. They can set you up with a complete matching ECM, camshaft and exhaust system.
Sincerely
Dennis Moore

Well, I guess that answers my question. Not much to be gained unless you really want to get the wallet out and go for it!

Okay BUDAH, here's a question foy you, if I did decide to whipple it how much rpm would I gain keeping the drive stock? I have heard that you can add a little pitch to blackhawk props but I have no idea if it's true. My boat only runs 4600 rpms trimmed where it rides the best. I have been doing the math and IF I could add 2" to my pitch and run at 5200 rpm that would give me about a 15 mph increase.

Tyle Crockett Marine has a system for the 502's that will take them to around 500 to 525 hp. It consists of reworking the heads, new cam shaft, roller rockers, honing the intake, re-programming the ecu, and a few other things I can't think of. All the parts cost around $2,000, and you would probably have $1,500 to $2,000 in someone installing it all.

Dennis Moore,

Wouldn't that cam--Comp Cams Xtreme Energy XE 268H - with a 110 LSA be causing reversion problems? Especially with stock exhaust.

Does anyone actually know someone who has run that Tyler Crocket system and can tell us of any success with it? I am always skeptical when it comes to engine builders who make statements regarding engine upgrades, especially when it comes to EFI. In my opinion, the only way to get an ecu re-mapped correctly is on a dyno.

They had a article in Hot Boat magazine about, I can't remember exaclty which month and year, but if I remember correctly they did put it on a dyno to get the actual results

I remember some of the mods in the article that Tyler Crocket did for Hot Boat Magazine. He took a stock 502MPI and added larger valves, different hydraulic roller cam profile, roller rocker arms, cut the heads .020", added larger 2.25" intake valves, reprogramed the ECU, and added CMI headers. I am pretty sure they didn't mention anything about PORTING of the heads---they probably just cleaned up radius's a little and I do NOT remember if they extrude honed the intake or not---i don't think they did, but they also put on a better air filter like a K&N or something. They ran it on the dyno and it made about another 100hp.

Pulling the engine(s), tearing them down, adding the parts and doing the mods---- especially the headers will cost probably close to about $5K per engine or better. The headers make it expensive (roughly $2,500 per set). Unless you want to keep it naturally aspirated, you could put a Whipple on it and you'd still make more power for about the same price. Lot's good input here from the others, but it is ultimately your decision of course. Hope all goes well whatever way you decide to go :)

Checkmate
Not really, water ingestion is a product of the intake and exhaust valves being open at the same time, called overlap. A relatively mild camshaft, with a moderate amount of duration, won't have a lot of overlap. A tight lobe centerline doesn't have much to do with overlap. Two degrees of additional overlap is all you will have between 110 and 112 LSA. An increase in overlap is much greater when you increase valve duration by 8 to 10 degrees on both the intake and exhaust lobes. Water ingestion from overlap doesn't really start effecting most big block marine engines until you get above 230 degrees intake and exhaust duration. Then you need a wider LSA. I believe a smaller duration cam with a tighter LSA will make more power than a larger duration camshaft with a wider LSA.
One last thing, intake manifold vacuum pulls the water into the cylinder through the open exhaust valve. A dual plane intake manifold will give the engine more vacuum than a single plane intake manifold. More water ingestion with a dual plane!
Dennis Moore

head work
 

Head work WILL make more power. It depends on who does the work.

Dennis

I will supply the head work, your dyno.

I have a 500EFI system for sale:)

I agree about the whipple being a much better way for $ vs horspower. But I really wasn't looking for THAT much extra hp. But, I guess if it's going to cost over $5k to get 100hp or so, it may be worth looking into a whipple. But. like I said before, I would have to regear my drive(not cheap on a blackhawk) and with my drive being so short, I really don't want to run 600+ hp because I would be worried about breaking my drive.

So, do you have to run a whipple at 6lbs or can you run them less?

Thanks Budah, I know 5200 would not be a feat! I was thinking the opposite that with 6lbs of boost and my gear ratio/prop I would want to over rev. So, I was thinking with some prop work if I could run the whipple at say 4lbs boost which would give me 550 hp(just guessing) maybe that would put me at my max speed speed for my current setup and be a LITTLE easier on the drive!

Does that make sense?

BUDAH, how long can you hold a supercharged motor WFO?