Rick252

I'm planning to buy another engine either a used Gen VI 454 0r 502. I want to bore the block about 30 over, put in some forged pistions and have the heads re-worked and larger valves added new cam and exhaust. My question is, what can be done with the stock fuel injection system ? Will raising the fuel pressure be enough. I really don't want a blower, because of cost but most of all reliabilty.

rjcardinal

Rick,

You are asking the same question as I did yesterday. Look at my thread titled Modifying a 502 EFI. I thought I would get several replies but the topic is quickly dropping to the bottom of the page. This is the most common engine in performance boats and I figured lots of people modifyed them but I guess not.

Good luck and post what you find out.

Ron

DonMan

Rick, as you know from my email, the MPI can be a source of limitation on a performance engine. The big question here is: Which MPI system are you using? The 7.4 MPI or the 454 Mag system? They are totally different. I will relay all that I have found out. I have spoke with Arizona Speed & Marine, Vortec and a few others. The consensus is you can modify either system with more psi at the injectors, recalibrate your ECM and even swap to bigger injectors (depending on your horsepower level). The biggest factor seems to be CFM flow through the throttle body. If you look at a throttle body on a 7.4 MPI and compare it to one from a 454 Mag, you will see what I`m talking about. Also, by comparing the two intake manifolds, you can easily see that the 454 Mag has a superior style design for pushing air. It is a big, tall intake compared to the 7.4 MPI intake. As I stated in my email to you, I am planning on swapping to a "Mag" style fuel injection. Later down the road, I want to get a lot more serious with my engine, and I truly feel like my current fuel injection will not support more than about 375-400 hp.

Rick252

Thanks fellows.
Don: you answered my question. I have the 7.4 MPI system. I'm glad to know it can be modified. I'm trying to get everything lined out before I get started and hopefully stop as many "surprises" as possible.

turbo2256

7.4 MPI

lets see ..Scat crank and rods ... blower pistons .... Edelbrock ported oval port heads .... custom roller turbo cam .... 7.4 MPI intake .... 2 turbo chargers ..... missing Electomotive engine managment system and one laptop. Will I get to it this next season. building three other engines right now and guy down the street wants more from his oval track car just lucky to get out on the water right now .... turning to page one of oval track rule book........

DonMan

Rick, What type of mods are you planning? According to ASM, the best mods for the 7.4 MPI would be: High-flow flame-arrestor, adjustable fuel pressure regulator, good exhaust system, high-perf camshaft and a recalibrated ECM. Anything more than this, they didn`t think you could get the required CFM from your current MPI system. I`m talking about things like: aftermarket heads, "big" camshaft and so on...

blown formula

Gentlemen....... your attention Please !!

ANY time you change to an adjustible fuel regulator the new regulator MUST be mounted as close to the fuel rail as possible or you cannot maintain pressure. If a rail mounted pressure gauge oscillates, you have a serious problem and do not use a oil/water dampened gauge. I have proof of that!!
Increasing the pressure only allows more fuel in during the interval the INJECTORS are open (interval is controlled by ECM).
Mercruiser MPI & Mag's are BULK injection. That is ALL injectors are open at the same time....Adding pressure is not an upgrade per se, but will be required to obtain gains from a cam or blower and have the engine live.
NOTE: if a Aeromotive fuel pump is used, be sure it was built or upgraded to the mechanically attached magnets in the pump. The old epoxy design was still used until MAY 2002. Our fuels/gasoline has alcohol & additives that destroy the epoxy in the old style pumps. Those epoxy particles the stop up your injectors & viola!!! fried engine!! Trust me on this! Call Aeromotive... they are very helpful.

audacity

no adjusting the psi is NOT the only thing you will have to do!...502 mpi can make 550hp NO PROBLEM...and have done it....make your life much easier....put a carbonmaker on it!

Shorty

I'm really nowhere near qualified to comment on this (as if that stops any of us) but seems common sense if the computer don't tell the injectors to squirt more, then how could you ever maintain the correct air/fuel ratio if you don't re-calibrate the ecm after the engine mods?

audacity

you can but an injector in tested and calibrated to flow X at Y...the EEC tell it time and durration...not how much!...one again you should play if your not for sure...like i said...bolt on a carbonmaker