"Dyno Exploring the 502 EFI" from Hot Boat
 

This is the four part series as printed in Hot Boat magazine from Jan to April, 1997. I'll start with part 1:
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dbkski, if you'd like I could e-mail these to you in higher resolution and more printer friendly format. I thought this might be of interest to others here though. I'll do part two ASAP.

I remember that article, i think I remember that the old KE headers, (back then were PF Marine headers) were the best of the bunch. I'm installing SM manifolds on my 2000 502 EFI's right now. Good article.
Dean

Yup, good stuff. I'm posting it on request. Here is part 2:
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:) :)

Nice find. I remember when Hot Boat magazine was the best one out there.

Yup, it was the best, at least as long as it was owned by Flynt. Part 3:
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Fourth and final part:
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Nice article Carl. Thanks for posting

I studied the entire article and what they ended up with is very close to a 525 EFI. They installed CMI headers, modified and ported the intake, did the same to the throttle body and did a lot of head work. Then they installed a roller cam with specs nearly the same as a 525 cam. They ended up with 543 hp @ 5,400 RPM. That happens to be where the rev limiter starts to hit on a 525 and is where I run my 525 on the top end. I've often read that the 525 actually puts out closer to 540 hp. The project engine made 594 Lb-ft torque @ 4,000 RPM where the 525 specs at 570 Ft-lb torque @ 3,800 RPM. The project engine was held to just a slight compression increase of the stock 8.75:1 which is the same as the 525. They also confirmed that with the lower compression ratio the engine runs best on 87 octane fuel and lost power with 92 octane. I will always run 87 octane in my 525 from now on unless I'm topping off old fuel.

I did a few projects with Jeff Koerner back then in the early days of MEFI 1 very nice to work with. Marine efi has come a long way since then. Great power from that manifold mod still works today.

I would think that you could purchase a performance intake and heads now for less money than all of that machining work.

Much less and better. Just saying if you keep the mpi manifold the mods are well worth the work

Hot Boat was my favorite performance boating magazine.

I sure do miss it.

I learned a lot from reading it.

Damn whered the article go!

I know that this is a SUPER OLD thread, but any chance someone has the articles still?

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I may still have the old magazines. I followed this back then and built a motor based on it. The guys name was Gary Knox If my memory serves me correctly, Speedstar Marine in AZ. If I can't find the article I do have all the specs. if that's what you are looking for. 502 MPI + 0.30, aluminum heads, 1.8 rockers, I think the lift was 648 on the Ultradyne cam, intake work and so on. Let me know if I can help.

Wanted to read through the article. I might be looking to upgrade next winter and wanted to see what was out there for the MPI. If you can't find it..specs are all I need.

With the factory manifold I dont think theres is alot of room for improvement. Best move would be decent cam, A decent set of heads, and convert it to a EFI manifold like this Pro-Flo

https://www.offshoreonly.com/article...om-stock-power
We've come up with a pretty good formula to balance cost vs power

Is this the son Johnny I met in Bimini last year? at the gas dock filling up buddies 32 Fountain that was one of the pace boats for the day

Im in the middle of putting LS engines in my Donzi, maybe I should do something with the heads/cam on the 502MPI engines I pulled out and throw on the engine dyno. What kind of air/fuel and timing do you guys usually run on those things, Im sure alot lazier than we do on our street/drag race stuff

Yes it is! Sure you should, great engines. 12.5/1 afr average. We use Pro Maxx heads on that package. Best bang for the buck there is. No reason to get crazy, they arent race engines. Shoot Jason an email with any questions on it. Hope you're well!
[email protected]

What exhaust are you using on the 454/502 MAG Stage 1, 2, and 3 upgrades? Thanks in advance!

Interesting I thought youd run much richer A/F ratios than what we do, but thats typically where we head for NA anyway. The LSA blown LSxs going in my Donzi I was thinking Id drive it to 10.5-11:1 a/f but thats prob being super overly conservative then LOL

Ive heard about the Pro Maxx supposed to be a pretty good casting actually especially for the money. I was looking at Summits iron heads as Ive seen tests where they picked up 40 over ported 088 castings and figured that be good enough for $750 but they look more promising still and not much more

EMI Thunder