[GregGold]

Im thinking of upgrading my dual quad setup to Holley's MPI. Im looking at their 99-119 product. Id like to know if anyone has one or has experience with them.

[JimM]

Greg,
I have a Holley Projection 4DI. It's a TBI system, but uses all the same electronics as the new MPI. See my post to Mike Brown above.

[1st & 2nd GENGuy]

The January 2000 issue of Car Craft has a section on injection swaps.

[GregGold]

Jim,

Does your fi setup control ignition timing? If so, can you elaborate on it, as far as the programming aspects of it?

Ive always wondered why a return line cant be 'T'ed into the supply line between the tank and the pump? Wouldnt that have the same effect/result?

Thanks,

Greg

[JimM]

Two excellent questions, that I didn't address before, but I should.

Ignition: this is a "Standard option". The Holley system has connectors for a late model electronic advance HEI, or a Holley electronic distributor, but you don't have to connect them. The knock sensor module is an extra, and it only works if you have an electronic advance distributor. I think an OEM knock sensor module will work, but I'm not sure. I bought a new mechanical/vacuam HEI before I got the EFI, so I was out of luck here.

Now for the ugly truth about the return line and the rest of the fuel system. I did, in fact, do exactly what you said. I'm running the a new 5/16 hard line for the return, and at the tank, I've attached it to the original 1/4 vapor return coming out of the tank, and also tee'd it into the supply. This does work, but it gets real ugly if you ever get air in the lines, such as running out of gas! The air slug runs around in circles and won't purge out, and you don't get any fuel pressure and the car won't run!

At any rate, the important thing is that the system be able to dump enough fuel at idle. The holley book says no more than 7 psi in the return line. There are fittings on the throttle body to connect pressure guages to the supply (supply pressure is 15 PSI)and return. You can tell if you're not dumping enough fuel because the computer will show the injection volume at minimum and the o2 will show it's still rich.

When I first set mine up, I used the whole vapor return line from the engine back. I had 11 psi return pressure (should be less than 7 psi)and a stinky rich idle. Runnning a new 5/16 hard line from the engine to the tank, and putting in the tee took care of that. After running out of gas, I crimped the bypass line off the tee, and the return pressure is still OK. So that's how I'm running now.

While this works, I don't recommend it. Pull the tank, bring the sending unit to someone with a welder, and have them weld in a 5/16, or 3/8" return line! I've had a lot of fuel system hassles, all my own fault for trying to take shortcuts, and all totally avoidable.

[GregGold]

Thanks again Jim.

Sounds like its well worth the effort in dropping the tank.
Would you recommend the holley electronic advance distributor?
As far as the knock sensor, Do you know if holley offers one?
How about a nitrous control? Ive read where some competitor efi systems come with a timing retard provision for nitrous. I wonder if holley has addressed that. Any ideas?

Thanks again.

[JimM]

Yes, Holley offers a knock sensor. There is some kind of black box that plugs into the tbi harness, and the sensor (an oem GM part) plugs into the box.

I have never had any detonation, with edelbrock 70cc aluminum heads on the 355 (~9.7 cr)I use mid grade unleaded

If I was to do it again, I would use the electronic spark advance, not sure if I'd go with Holley or HEI dist.

I imagine that if you use an hei, any MSD stuff would be useable as well.

I'm not aware of any provisions for nitrous applications in the holley efi stuff, but it would be easy to program a high rpm retard into the spark curve. I wouldn't dare try to use the efi to add additional fuel for nitrous, but if you use the fuel sprayers that come with the nitrous kit, you could use the efi cpu to "fine tune" the mixture with the nitrous on

There are two wires in the harness labelled "Not used". I don't know what they do, and I haven't asked.

[This message has been edited by JimM (edited 12-16-99).]

[This message has been edited by JimM (edited 12-16-99).]

[GregGold]

Thanks Jim. I feel better about the holley product. The accel product looks more appealing but the price doesnt. I cant see paying another grand and getting basically the same thing. If I had the extra grand, Id direct it towards an overdrive or the like.

Thanks again.