MPI compatability
 

I have a set of 1994 454 mag efi units. I have two freinds interested in putting them on 330hp units. Can this be done?

No
 

The intake ports are a big mismatch. The 330 has a small oval port and the Mag EFI has a large rectangle port. The intake manifolds are different.
Sincerely
Dennis Moore

Aren't the mag efi units port injected?
Why couldn't they use some filler epoxy and build-in the ports in the manifold to approximate the head openings? That would minimize turbulence and injecting at the port would eliminate the fuel dropping out of suspension due to low runner velocity.

Thoughts?

mcollinstn,

Yes they are port injected.

Dennis,

Thanks for the info...

Merc used that rectangle port EFI system on the peanut port 7.4 EFI engines in late '96 & 97. The engines were called 7.4LX and rated at 330 PSHP. So, even thought there is a port mismatch it appears to still have been worth a 30 PSHP gain on the 300 HP 7.4. The mismatch does not seem to be as critical in a port injection environment since the fuel is injected directly into the port. However ECU programming would be quite a bit different than the Mag.

bobl,

I can't help but figure the LX's you mention were running a different cam than the 300/310hp 7.4MPI's. (I have no data to back that up though).

I am currently converting my 330 7.4 into a MAG. I have the heads and all the fuel injection stuff including the cam geting heads shaved to try to get the compression up on the 8.0-1 pistons hope it works out .

Keep it under 5000 rpm.

Depends on which 330 you are talking about,,, I would assume you mean a carb 330. My 97 7.4LX MPI was 330hp and had the same injection system as the mags.

Re: No
 

The stock Merc manifold for carbed 330 engines uses a large oval port intake manifold with the small oval port heads which is pretty much the same mismatch as using the MAG efi manifold would be. So its not optimum but no worse a mismatch than the stock carbed engine.

This is because actually the efi manifold is not a large rectangular port. The ports are very rectangular but are some what narrower and shorter then rect port heads. They are actually the same size as the large oval port heads except the rectangular shape means they mismatch in the corners and the floors are a little higher but they are quite a bit, 3/16 " narrower and 3/8" shorter then rectangular port heads and so,,,, the MAG efi manifold is a mismatch no matter what heads you use, something that I always thought odd.

These are avg dimensions from some heads and manifolds I have measured over the years. as you can see the merc manifold is a closer match to the oval ports altho with square corners the heads would need some work as large manifold to smaller head is worse then smal manifold to larger head because of the step created in the flow path.

GM Large rec ports 1.6" x 2.35"
GM Large oval 1.5" x 1.9"
GM peanut oval 1.5" x 1.4"

Merc Mag efi manifold 1.4" x 1.9"