Using my 454 mpi intake on a bored 502
 

Im building a 502 to replace my current 454 mercruiser. Bored .020 over, dart heads, should be around 600 hp once complete. My question is the mpi mercruiser intake does fit the 502, but is it going to perform up to par on the bigger motor? Or should i buy a carb instead. Also will the computer work with the new motor?

Just a guess, the intake was designed to work on the stock 454 and the ecm was programmed to work on the stock 454, what is the stock HP of the 454 vs what you expect to get out of the new motor. If the intake doesn't hold it back you will probably run lean.

I would say unless your 454 was a 454MPI horizon (385hp) with high rise intake I wouldn't use it on a 502

600hp, if the cam, heads, compression, and exhaust will support it...means throw the 454mpi and 502MPI intake in the trash. Even the 500EFI intake has a hard time getting their.

GEtting something like this with supporting hardware and computer will get her done:

Edit in: Holley made the below intake available with brass passages for marine..not sure if they still do.

https://rspimages.holley.com/9901-203.jpg

Is your 454 a 454 mag or MPI. Totally different intakes. One is for Peanut Port"MPI" and the other is for Rec Port "Mag". I think all 502's are rec port so thats your first hurdle is figuring out what you have.
This is an MPI https://www.youtube.com/watch?v=DjKNG7LhOao

This is a Mag. http://www.mycobalt.net/2009/07/23/2...-223-for-sale/

Mag has the intake with the air cleaner making a turn to starbord.

Chris

If your engine is a MAG, the 454 and 502 MAGS use the same intake. And your computer will need to be programmed for the additional hp anyway. But, as SB stated those intakes won't flow enough to support 600hp.

You'd probably need new injectors as well and at the end of the day wish that you just fresh with a new Holley EFI system or the like. You could luck out and have it be perfect, but the stock equipment is just so unfriendly to any sort of adjustment. I looked into using my 454 mag system on my 502 and just threw a quickfuel carb on it and have been happy with that. I think that you'd have to use the original cam as well.

if the 454 was a mag motor that the mpi setup came off every part is the same inc injectors .the only diff is the ecm has to be remapped to a stock 502 setup .ask me how I know ive done many the cost for remap is 100.00 .never had 1 issue

You might need larger injectors.. They are not that expensive if you get them from rock auto. Yow will probably need and adjustable fuel regulator. As far as cam i would "think" a 500 efi cam would be drop in. Give bob a call at Marine Kenetics, think thats the name, and ask him. If you have a Mag Intake then I think this is totally dooable. Get the PCM flashed by someone like maybe whipple and your good to go. Not 600 hp but maybe close to 500

Chris

Another option and probably a better one is sell your entire MPI setup including Intake, cool fuel , PCM Dist and everything and Call Haxberry and order Holley. He can tune over the net to some degree. Prob get about 900-1100 for your current mpi setup.

Chris

Smokin gun hit it square . Rc injectors .,remap , maybe the tb mod . Assuming you have the the right heads cam exhaust it will get the job done .

Mine dyno'ed at 545 and 617 Tq not using my EMI thunder exhaust, used dry exhaust and muffler during test. Engine mild mild porting on the intake, cut top of runners off, opened up stock cast iron heads slightly, cut down valve guides, bored .030 by Young Perf. Don't know what the cam profile is, and he said the only way to get more is a larger TB. I need torque more then HP so we stuck with modified stock intake. Yours being a lighter boat the Holley EFI systems with Intake might be the way to go. Just my opinion

But mine is a 502

I believe I read on here that the 502 / 454 mag MPI intake stops flowing right around the 550 hp mark.

As stated, the mpi intake is a restriction, cut down top of runners, port match it, have it ported if possible (very hard to find anyone interested in porting one properly as there are LOOOONG runners that virtually nothing can reach), buy a bored out throttle body (I use one and have a spare if interested) and a remap will be necessary on ecu. The stock injectors on a mefi 3 will support 600 hp no problem, I hear the older mefi with the fat injectors flow less fuel, you might need to turn up fuel pressure. I made 700+ hp blown with stock injectors at 78 psi fuel pressure. I made 650 hp NA on my 540 using a modified mpi intake and bored throttle body and well over a 1000 hp boosted. Is it worth all the pizzing around, well thats another story, buy a good std intake set up for efi,fuel rails, a scorpion or fast throttle body and use your stock ecu and wiring harness is another route IF you have someone competent who can tune it on the water. Buy a holley efi set up if you want the least amount of trouble getting it tuned or just bolt on a traditional carb, intake and distributor if you want to get out cheap. IF yours is mefi3 the ecu, unmolested harness and intake IF not rotted in water crossovers are highly sought after and you could probably get enough out of them to buy a new carb, intake and distributor, fwiw, Smitty