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502 mpi procharger fuel system questions

Old 03-19-2013, 04:44 PM
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Here ya go Gris. This is one in the shop now. We also redrilled the fuel rail and the intake to accept 65lb. injectors. It is one of the older style rails that had the Kiehin injectors and there are no direct replacements that are larger. The later model rails are quite a bit easier.
Eddie
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Old 03-19-2013, 05:37 PM
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Exactly what I was looking for Eddie, much appreciated.

From what I see, the fittings are on top of each other and only one comes from the regulator? The other seems to direct downward. What is the hose running across the valve cover?

Last edited by Griswald; 03-19-2013 at 05:59 PM.
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Old 03-19-2013, 06:31 PM
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In that style rail, the fittings are held into the rear of the rail by a retainer plate. The fittings have O-rings on them, so the holes don't have any threads. We drill and tap the holes for 1/4"NPT.They have to be tapped pretty deep so that the fittings clear the distributor. We also have to cut the back off of the rail on a 45* angle to clear the fittings. We put it in the mill and cut off quite a bit so the fittings clear. Originally, the rail was feed into the top passage, it went forward to the regulator, and then returned through the lower passage. The problem with the rails is that the passages are small. If you plan on making any amount of power, you have to feed the rail from both ends so that you don't run one end of the rail dry. The other issue is that if you install a larger fuel pump, then the regulator can't bypass enough fuel at idle.

We block off the regulator internally so that it no longer works. Once we do that, there is no connection from the top passage (feed) to the lower passage (return). We then come in from the bottom of the rail in the middle and drill through both passages. We tap the outside of it and put a plug in it so that the fuel doesn't leak out. This hole now connects the 2 passages together. The fuel then runs out the rear lower passage and to the regulator where it is returned to the tank.

We come out of the pump and run a #10 line into a Y-block. It then splits into (2) #6 lines that run to both the front and the rear of the rail.That hose you see running along the valve cover is going to the front of the rail.

Hope this helps. It's hard to explain. It is a very time consuming job to do. There are other things that need to be done, like drilling out the #7 injector hole. Let me know if you have any other questions.
Thanks,
Eddie
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Old 03-19-2013, 06:59 PM
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I have a '97 mpi with the Kiehin injectors as well and have already bored #7. I dead head the rail and return from the regulator back to the inlet of the sx pump. Haven't had an issue that I'm aware of and have been running it that way for 3yrs now. Thought about ditching the mpi and going with a single plane but can't seem to justify the want vs need at this point. I appreciate your comments.
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Old 03-20-2013, 07:46 AM
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We have found, with the larger pumps, that returning the fuel to the inlet of the pump can possibly cause some issues. It will certainly work in some cases. I don't have the benefit of monitoring every setup on a continuous basis. Once finished, we give them back to the customer. I have to know that it will work all day, every day. By returning to the tank, I know for certain that it will work, no matter the situation. Basically, i have to make it dummy proof. There is always more than one way to get a job done. This is what we have found to work well for us. The engine in the pic has an M3 Procharger and made just shy of 900 hp. We have used the exact setup in the pics to support near 1000 hp.

Give me a shout if you have any questions Gris. I'll be glad to help whenever I can.
Thanks,
Eddie
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Old 05-19-2013, 08:19 PM
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To the top.

I'm reworking the fuel setup on my 502 Mag because the VST failed and i have to say, Eddie your idea on the fuel rail look much better than mine. I was just going to snip off the factory hoses and tie them to my new hoses with some barbed brass fittings and hose clamps.

Thanks for the tip.
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Old 05-22-2013, 12:46 PM
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If you got the ECM remapped wouldn't that negate the need for a fuel pressure increase with boost pressure?
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Old 05-22-2013, 01:11 PM
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Originally Posted by korvetkeith
If you got the ECM remapped wouldn't that negate the need for a fuel pressure increase with boost pressure?
If the injectors were large enough, you could compensate for this in the programming. Remember that boost in the intake tract negates fuel pressure. So if you run 43psi while in vacuum, if you don't raise FP with boost, each pound of boost effectively reduces fuel pressure by the same amount. If the engine gets 10psi, then that would be like only having 33psi of fuel pressure to work with. The size of the injectors needed to get an appropriate amount of fuel at 33psi would be much larger. By raising fuel pressure at the same rate as boost, in effect you keep the fuel pressure static.
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Old 01-27-2014, 08:59 AM
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Does anyone have a picture of a machined fuel rail before it's installed?
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Old 01-27-2014, 09:19 AM
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I have some. Pm your email address and I'll forward.
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