robyw1

I think the upgrades didn't help because you are at the max for the components you have.

Roby

502procharger

a used procharger or whipple with 5-6lbs of boost will make a world of diff.

Outdrive1

I did all the mods you did on my 502 mag efi and I didnt really notice any difference at all. I bought a set of Lightning stainless headers and it made a world of difference. About 400 rpm. I used to run a 22 pitch bravo at 5000 rpm, now I can pull it about 5400 with a gain of 4 or 5 honest mph. It still wasn't enough so I'm putting a vortech blower on it, Im lucky enough to live 20 minutes from Az Speed and Marine, they are supposed to be the best. I should have it back any day now (its been three weeks). Back to the subject at hand, I would invest in a set a headers because they will give you some real bang for buck and it will help with any future mods. Not only that they are about 100 pounds lighter (or they seem to be) and they look cool. Try and find a used set of CMI's, Lightnings or Imco's. Dont waste your money on the cheap Eddie Marines (no offense to the guys who have them) but I think you get what you pay for.

L9X25

This thread is depressing!

I'm at the begining of this path with a totally stock 454 Mag MPI and have been contemplating many of the mods just discussed (exhaust, cam, headwork) and would be VERY disappointed with no improvement.

It sounds as if the EFI is the limiting factor. Possibly a larger throttle body, larger injectors, some extrude honing would make a significant difference? Sombody must have had this motor on a dyno and checked the A/F ratio. Anbody have any insight?
I would hate to go back to the world of carbs.

robyw1

The EFI is not the limiting factor. You can modify the engine in anyway you want and just like a carb upgrade will be needed an EFI upgrade will be needed. A properly set up EFI system will always be better than a properly set up carburetor any day.

As far as extrude honing Have the intake honed as smooth as possible down to the injector. From the injector on through the intake port it should have a slight texture to promote proper fuel atomization.

Roby

L9X25

Roby,

I am puzzled by the unresponsiveness of the 454 Mag MPI. The lower HP motors usually respond very well to upgrades ... it's the already close to max motors that are more difficult (costly) to improve.

I agree 100% that EFI should produce more power while remaining more docile than a carbed engine.

What is the big restriction on these motors that is making the external mods irrelevant?

Leo

kmhp

how do you bump up fuel presher

H2Xmark

junk the factory ecm and get a motec or similar system, then you can map your ecm on a lap top computer at your house, you might call Dustin at Whipple he is great on the ecm recal.

Pat McPherson

I am with formulaz583 on this one...
For those of us that like to tinker or do our own work to save some money, a carb is the way to go.
I believe robyw1 has a lot of experience working with MPI systems so it is different for him.
There are some engine builders that do have dyno proven combinations that will add 80 to 100HP to a 454 or 502MPI. Problem is that they cost like $4,500 and you need to tare the engine down.
For that kind of money, you may as well buy a blower and bolt on 160HP.

pkspx

Correct the 454 EFI engine is useless unless you go carb like i did. While the engine was out heavy mods were done I can list detail parts and include dyno plots if you want, I have 515hp not bad for a 454! The boat will cruise at about 74MPH top speed GPS. Thats as fast as some TWIN ENGINE BOATS!

Lots of love for the 454 hehe Now go out and start modding the thing! If you want to take another look at my pics here

www.customtints.com/454/done1.JPG