MCKILLOP

Curious about this as well? I know Hardin makes an adjustable fuel pressure regulator add on for 502 mpi's. That would probably work pretty well with this set up.

Inspector

Haxby, can you provide details of the intake modificaitons?
Thanks.

audacity

he changed the length of the dividers to replicate a different length runner. I have played and tuned that length...which I've spent a lot of time and $ doing....I'm sure this gentleman would be happy to take your parts and modify them for your needs???...just speculating here.

you can make a bunch of power with a 502 MPI and I've done it. I would not recommend it to ANYONE that doesn't have a lot of engine background a, dyno and all the equipment to build and test it every step of the way....Pull your MPI's and send them to someone like this guy that does it for a living. i know many that tossed the mpi system and replaced it with carb setups.

as a side note i never liked the 500 efi's....i always used the 500hp carbs in the race boats until i was forced to use the 525's....they look cooler and make more power than advertised and can easily make more within minutes.

thanks for sharing your thread with us OSO'ers

dbkski

The Hot Boats articles!
http://www.offshoreonly.com/forums/g...-hot-boat.html

Smitty's play by play!
http://www.offshoreonly.com/forums/g...ghlight=intake

Inspector

That's funny, I have those old magazines and was just wondering if Haxby had a different mod for the intake.

HaxbySpeed

I cut down the tops and opened them up, and cut down the dividers. I went as deep as I could in the ports from both sides to blend it all in. I later tried an extrude honed intake but didn't pick up anything significant over the original mods, the extra flow may have helped a more aggressive build but this one has a mild cam and is still the stock compression. The heads are completely stock with just a bit of clean up work. We originally did the engine two years ago but didn't have time to dyno it. It ran flawlessly for about 60 hours until an injector quit and took out a cylinder. Luckily it was right at the end of our short season here so we re-did it last spring and got a chance to dyno it. It got about 120 hours on last year and other then some electrical gremlins has been trouble free. The engine quit a couple times due to a bad connector in the MEFI harness, and for some reason it went through two IAC motors. Rather then messing around with old wiring and the old MEFI I decided to yank it all off and throw on a Vic Jr intake with Holley throttle body EFI. Should be on the dyno next week, I'll post the results as soon as they're done.

verbi69

Tries sending you a PM but your box is full......interested in making more power in my 525's...sorry for the highjack.

Mike

HaxbySpeed

So, we pulled off the old ported intake, installed an untouched Vic Jr. and a Holley 900cfm TBI unit and changed nothing else.. Here's the results. Interestingly, and this ties in with another thread in general tech right now, the 2" oval flame arrestor cost about 20hp and a bunch of torque. I think the long narrow passage an the sharp angled entry really killed it. It's not a big deal for this app. but definitely worth noting. Without that restiction this thing is solidly in 500EFI territory power wise. This was on 87 octane too.

snapmorgan

Haxby, I believe that I have the white painted, ported and extrude honed manifold that came off this engine. I was planning on putting it on my 540 along with a larger throttle body. I think the stock intake is killing my top end as it will only turn about 5100rpm no matter what prop i put on it. Do you think this is going to be enough intake, or should I scrap it and put on something else? I have about 575hp now and looking for about 625. Also plan on dynoing before and after the intake swap to see exactly what happens.

Engine is 540CI, Edelbrock rect port marine heads, Madara custom cam, 9.2-1 compression, Imco powerflow exhaust.

I am really looking for a few more rpm than anything else. Maybe 5600-5800.
Thanks

mr3dman

I would call Bob back and ask him what intake would work best with his cam. He would know what rpm that cam would fall off at, and why you are stuck at 5100 if the cam has more rpm's left. imo...