crmax

can I put the cam from the 7.4 385 horse version mpi into the 7.4 310 mpi?

SledgeHammer

I am no tech guru, and do not know the answer to your question. It may be possible, but I think there might be other issues. The Mag motor has a rev limit at 5,200 RPM's. Our 7.4MPI only goes to 4,600. We have cast pistons and a cast crank, so reving to 5,200 is not good. I think we can rev safely above 4,600, but I'm not sure the 7.4 MPI would hold up at 5,200. If it will, you will also have to get the rev limiter changed or you won't get all the horse power out of the cam. I hope someone with more knowledge jumps in on this. As an owner of a 7.4 MPI, I would like to know if anyone does recommend a cam for this motor that will give an increase that can be seen on the speedometer.

cheitman

The 7.4's biggest downfall is the peanut port heads. Any cam change would require a better flowing head to see any improvement. I just rebuilt my 1996 7.4 and was planning on changing the cam and porting the heads. My machine shop said it would be a waste of time to spend money on the small port heads. I put it back to stock and plan to build a 540, possibly blown, next year. That way I will have the fresh 7.4 for a reliable spare!

mcollinstn

A 7.4 mpi's biggest restriction is its intake system.

Go to a carb and 4-barrel and you can cam yourself to some decent hp. The 385 hp cam is not a good choice, though.

A 7.4 MPI is a good unit as it sits. Can't do a lot to it affordably and get much in returns.

crmax

cheitman,
the 7.4 mpi dose not have the peanut port heads they use the vortec heads,
Ray,
the cam in the 385 version is not the reason it revs to 5200, the heads on that flow better at high rpms I would like a cam that has more duration and if I can get a used cam I may give it a try
mcollinstn,
Ive been thinking alot about swithing to a carb but I want to give the mpi a chance, my gaol is around a 5 mph gain

bobl

I'm currently working on that engine in Searay Jim's boat and I'll share what I know. I ported the Vortec heads, installed large valves and installed a Comp cams hydraulic roller cam. There are 2 major stumbling blocks with the fuel injection. First the throttle body is very small. It only flows about 500 CFM. Secondly it has 22 lb. injectors. I did some work on the intake and throttle body to get a little more air flow. At that point it was extremely lean. I reprogrammed the ECU, but couldn't get enough pulse width. I had to raise the fuel pressure to 60lbs to get it rich enough at WOT and the engine won't idle with that kind of pressure. So, the injectors are too small to support the air flow even that small intake/throttle body will flow. I've switched to 36 lb. injectors now, requiring starting all over on the programming. We have picked up about 5 MPH, which translates to about 375-385 HP. In reality, that is way more hassle than it's worth. I'd recommend going to a carb if possible, or aftermarket EFI if you must stay with fuel injection. That will get well over 400 HP. As far as a cam swap, it's not worth the hassle to change only the cam. Going to an after market cam with low lift would be a better choice. You cannot run much more lift than stock without cutting the guides down on those heads. The retainers will hit the guides.

Bob

cheitman

My 7.4 is the carb. version. The mpi must use the better heads.

Madmax

We performed this swap on a friend of mine's 96 baja with the carb motor. With this cam, new timing chain, and an Edelbrock performer RPM intake, he picked up a solid 2 mph. It's a drop in cam with no spring changes needed. Lift is only .483 on this cam. Has a very nice sound to it also at idle. You decide wether it's worth the trouble. Cost is nothing, this cam can be bought for 40 bucks on e-bay.....shop around. Also www.competitionproducts.com has this cam.

o, by the way, power range didn't change much at all. His will rev to 5 grand easily. 96's don't have a rev limiter.

enjoy.!

crmax

bobl,
thanks for the info, I guess its cheaper going back to plan A, change to a carb.wow only 500 cfm now I know why those motoers didnt make alot more power than the 330s. any idea how much power just changing to a carb will get me??

mcollinstn

Just changing to a carb - virtually no gain.

Carb, performer RPM intake, aftermarket cam with lift less than .520 and duration around 215-220@050 with a 114-115 lobe center...

Give you a solid 60-70 hp.