FPR psi/inHg relationship, question

[Schmieder]

Does anyone have or know of a chart for the GM FPR and what pressures it provides in relation to manifold vacuum in inHg?

Or if anyone knows....what are these...

0 inHg = ?? fuel psi
7.35 inHg = ?? fuel psi
14.7 inHg = ?? fuel psi

[Azrael]

For the older FPR's: WOT/zero vacuum = 45 psi. Idle vacuum (~18 in-hg) should be around 37-39 psi IIRC.

Newer 00+ FPRs are 55 psi at zero vacuum. No idea about idle but likely a similar difference to above.

[86FieroSEv6]

Failing that, you could hook up a fuel pressure gauge and use a mighty vac or similar device to supply a controlled/measured amount of vacuum to create your own matrix.

[Syclone1452]

All of the OE regulators I know of are 1:1. You will see + 1 psi of fuel pressure for each psi of boost in your manifold. And, you'll drop .491154 psi for every inHg of vacuum you're pulling. 2.03 inHg = 1psi. vacuum is just anti-boost <grin>

Rising-rate regulators and FMUs are setup to provide more than one psi rise of fuel pressure for each psi of boost. I don't like 'em 'cause with a 12:1 FMU for example, the regulator will be asking for an additional 60 psi of fuel pressure for only 5 psi of boost. If your base is 45 psi, that will attempt to force your fuel pump to generate 105 psi of fuel pressure. At that pressure, most fuel pumps won't flow enough fuel to feed a Geo Metro... not to mention what your injectors are going to do with 105 psi behind them... Stick with a 1:1 FPR

[Schmieder]

For the older FPR's: WOT/zero vacuum = 45 psi. Idle vacuum (~18 in-hg) should be around 37-39 psi IIRC.

Newer 00+ FPRs are 55 psi at zero vacuum. No idea about idle but likely a similar difference to above.

Thanks

Failing that, you could hook up a fuel pressure gauge and use a mighty vac or similar device to supply a controlled/measured amount of vacuum to create your own matrix.

Interesting because I have a manual boost controller bolted in the engine bay but isn't being used atm. Ends up the spring itself tops at 8psi. It hits 7psi then gradually builds to 8psi over the wot run.

I also have a spare vacuum gauge.

I could use the MBC to have a controlled vacuum and the spare gauge could tell me the vacuum in inHg in the line past the MBC. So I could boost up pressures at idle and light load. It should provide a finer mist of sprayed fuel. And a finer mist = more power per part fuel. It may even help the turbo spool up faster, yet it spools very quick as it is now.

All of the OE regulators I know of are 1:1. You will see + 1 psi of fuel pressure for each psi of boost in your manifold. And, you'll drop .491154 psi for every inHg of vacuum you're pulling. 2.03 inHg = 1psi. vacuum is just anti-boost <grin>

I like your attention to details. This is what I was looing for, hard numbers. Now I can start working out some charts.

Thanks, best answer yet.

edit:

All of the OE regulators I know of are 1:1. You will see + 1 psi of fuel pressure for each psi of boost in your manifold.

I use a check valve to my FPR so no boost there. But are you saying I'll get positive pressures in the fuel rail if I have boost psi on my FPR? GM stock FPR for a 96 Grand Prix SE 3100. Is the stock FPR in my built to withstand 8psi safely or is that harmfull to my FPR?

Thanks for taking the time to answer my questions.

[Syclone1452]

I use a check valve to my FPR so no boost there. But are you saying I'll get positive pressures in the fuel rail if I have boost psi on my FPR? GM stock FPR for a 96 Grand Prix SE 3100. Is the stock FPR in my built to withstand 8psi safely or is that harmfull to my FPR?

remove that check valve... you really need the increased fuel pressure...

With boost, you get the intake pushing back against the injectors, so a 45 psi base will actually be lowered with every psi of boost. You need to increase the pressure in the rail... just to maintain the same relative fuel pressure in the intake.

... thinking about the Syclone and Grand National...
you need a check valve in the line to the brake booster, possilby one in the line to the EGR, and maybe one to the vacuum reservoir

Happy Resurrection Day!!