OK you LT1 guys, I have a question

[cmaje72]

I can tell you for sure that with the vacuum disconnected on my 93 LT1 fuel pressure is 43.5psi.

[EagleMark]

I can tell you for sure that with the vacuum disconnected on my 93 LT1 fuel pressure is 43.5psi.

My 94 too!
But just like GM specs for TBI there is a varible, I don't know why they did this as it is not correct. TBI specs are 9 to 13 PSI? Wrong! I don't care what GM service manuals say! It may run at 9PSI but the lower you go from 13PSI the worse things get. I have never seen one higher then 13.5PSI. These are all done on my same ol trusted gauge.

For instance, I have never worked on a stock engine in person that ran well at anything other than 13PSI. As a matter of fact if it is not 13PSI I usually find something wrong like a pump or clogged filter then when fixed it's 13PSI. If it's higher than 13PSI it's usually a ubstruction in the return line. Check return line pressure and should be 0PSI. If it's 2PSI you will usually find inlet line 2PSI higher.

They may have varibles to compensate for gauge differences. I have checked cars set to xxPSI on their gauge and it is yyPSI on my gauge. I have seen diffences as much as 4PSI on gauges.

[JeepsAndGuns]

Ok, I think I understand what your saying now. So basicly its like a siphon or suction effect, where the higher vaccume of the engine at low load is actually kinda helping to suck the fuel out of the injector, then at low/no vaccume, the fuel is simply being pushed out the injector by the fuel pressure alone. So at high vac, its sucking the fuel out, so less pressure is given so they dont flow as much, then low/no vac, pressure goes up for more flow.
Do I have that more or less right?

[Six_Shooter]

No, not really, don't think of it like a siphoning, that would require a different principal.

It's just simply pressure differential. The pressure difference between the fuel rail and the intake runner in this case. The vacuum referenced FPR is used to keep this pressure difference more or less the same at all engine loads.

[JeepsAndGuns]

If its not like the vaccume is basicly helping to suck the fuel from the injector than I just dont understand what your talking about.
But you know way more than I do and I value your advice. So I will run the vaccume line to it. So in the bin where you enter your injector flow, do you enter the flow when the vac line is unhooked?