Lift pump pressure and injection pump timing

Hello everyone. just had this rattling around in my head. I read about about an old McCulloch centrifugal supercharger installation and in it was a modification for the lift pump. They had put a hose port on the atmosphere orifice on the lift pump and routed it to the boost side of the compressor. Thus altering the spring rate under boost pressure. I know it's for a gasser setup and there was vacuum also run to the same modified atmosphere port. (They were trying to maintain steady fuel pressure for a blown threw carb system). So my thoughts were this might have some application to our diesel engine that have been turbo charged.
The McCulloch modified lift pump from what I gathered made an additional 2-3psi more pressure under 5-7lbs boost. My question is to the folks who are more savvy with injection pump timing than myself. How would variable lift pump pressure affect injection pump timing?

From what I understand you want lift pump pressure to stay consistent. With more pressure it advances the timing and less pressure retards the timing but the trucks want stable timing.

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There’s been quite a bit of discussion around this. Here is a pretty good starting point.

https://www.oilburners.net/threads/official-test-results-of-fuel-inlet-presure-timing.34636/page-1

The punch line is Mel says you loose about 1/4 degree off the advance curve for every psi over stock (4-5 psi). Now I’ll be honest and say that that I’m still not sure I fully understand exactly what that means. Maybe one of the pump guys would like to chime in and help out.

Thanks for the reply guys! Laserjock I noticed in those test results, most people were referring to a constant higher fuel pressure. I was thinking more along the lines of a variable pressure that increases with boost. I noticed that Macrobb recorded fuel pressure at idle of 4psi and dropped at cruse and he suggested a possible 2.5psi at wot. I think that the mechanical lift pump mod that I was referring to might help keep the fuel supply pressure at a constant 5-6psi throughout rpm? Depending of course on what you pump pressure is at idle.

RetiringColt said:

I know it's for a gasser setup and there was vacuum also run to the same modified atmosphere port. (They were trying to maintain steady fuel pressure for a blown threw carb system). So my thoughts were this might have some application to our diesel engine that have been turbo charged.

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The carb works on pressure differential. Pushing boost through it means the ``vacuum'' created by the venturi is likely to be higher pressure than the output of the fuel pump.

There is no connection between diesel manifold pressure and the diesel injection system. The very good reason for doing this on the old gasser is totally inapplicable here.

Increasing fuel pressure changes the injection advance, and there is no reason to think we want to do that in response to changing manifold pressure.

I run 15 psi in my ranchero all the time.
altho I don't have numbers of how much the extra 10 psi changed the timing.
I did time it after fuel pressure increase to 9*
I don't even get a drop of pressure loss at WOT making 25 psi

@IDIoit what pump at you running? And are you running a regulator?

Oldiron said:

@IDIoit what pump at you running? And are you running a regulator?

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X2

I think you run Holley reds. Are you regulating them?

holley black. has a regulator, but no real need to, its WOT