Uber fuel pressure regulator confusion

[JeepsAndGuns]

We talked about this in one of my oother threads. I found out my edelbrock fuel rail uses a LT1 style FPR.
Well I do a little searching online and I found that the LT1 was not the only gm engine to use the style of FPR. Craploads of vehicles use them!
I stumbled upon one on amazon and there is no real discription of it. At the bottom they show what other people have looked at. I found 6 delphi FPR's that look identical, but with just diffrent part numbers. Nothing in the discriptions about what their pressures are, or what the diffrence in them are. They all would bolt onto my fuel rail. But what pressures are they set at? I tried searching, but had no luck,
Part numbers I found where they all look identical:
FP10003
FP10004
FP10020
FP10026
FP10027
FP10300

Advance auto offeres a BWD brand adjustable one for like $56. I am thinking about just getting that one.

[EagleMark]

I have an LT1! Never really looked at the regulator and right now the car has at least 2 feet of snow on it, but I thought they were vacuum regulated. Wait! I know they are because fuel pressure at idle is 43.5 and raises like 5-6 pounds at low vacuum.

Maybe look it up on Rock Auto. 1994 or 95 should be the same. Probably 1996 - 97 too...same motor PCM etc... went OBDII but they added a crank sensor. Why? I don't know, must have been a law because the optispark distributor already did that.

[JeepsAndGuns]

Yea, they are all vaccume refrenced, and they have pictures and look identical! So there must be some type of diffrence in either max fuel pressure, or the ammount of pressure drop when vac is applied.

So the LT1 is 43.5 WITH vaccume applied, and then goes up? Humm, we talked about it in another thread and I thought the 43.5 psi was the max pressure, meaning what it is with no vac. I thought that was how FPR's were rated. I know the FPR on the 4.0 in my wrangler is a 39 psi regulator. Thats the pressure with the vac disconnected. Its also the only pressure the repair manual gives, because with vac applied, it can vary depending on how much vac is applied. But it drops a few pounds.
So if the 43.5 psi is with vac, then its probably gonna be something like 45 psi with no vac. Thats too much pressure for the injectors I am running. I will be drowning my engine.
From the rough calculations, I was estimating somewhere around 40-42 psi should be about right. 43.5 psi would have been right at the limit, and a bit on the high side, but I think it would have been ok. But now that I know thats not the max psi, I think the adjustable one is gonna be the way to go. For me anyways.

[EagleMark]

There's only one on Rock Auto that is cheaper than the one you found adjustable and it's plastic (maybe black metal). All the others were metal and more money.

[JeepsAndGuns]

Thats what all of the above mentioned ones looked like, And is identical to the bad one I got from the junkyard. Its black painted metal.
Heres the adjustable one from advance auto.
http://shop.advanceautoparts.com/web...R%7CGRPFUELAMS_____#

[EagleMark]

Still vacuum reference and adjustable! Priced right! May be your answer...

[JeepsAndGuns]

Still vacuum reference and adjustable! Priced right! May be your answer...

I believe so too. I have decided to get that one. I think having the flexability of a adjustable FPR will be real handy, seeing as this is not a stock gm engine with stock components.

One question, when I set the fuel injector flow in the 7427 bin, do I set it for the flow with the vac line connected, or when there is no vac. I'm thinking with no vac? The tbi uses the same pressure all the time, and with this one being vac refrenced, it changes. Will that cause any problems, since the computer is expecting a constant pressure, but its actually getting a varying pressure?

[EagleMark]

There is no answer to that? Since 427 has no vacuum referenced fuel pressure regulator from factory. MPFI is a hack.

You are mixing and matching parts so it's going to be a tune issue. But I would start with vacuum on at pressure you figured from calculator. WOT goes low vacuum and increases fuel which is what you want. Then see where tune is. Then maybe see if regulator with no vacuum adjusted to your pressure does better... There is more to this that Six Shooter explained in another thread that I don't remember how it works on injector because of vacuum at idle and no vacuum at WOT

Just looked in my MPFI LT1 XDF and fuel injector pounds per hour is set at 43.5 which would be with vacuum.

[JeepsAndGuns]

I can set the no vac fuel pressure with the engine not running by simply hot wiring the fuel pump. But I wont be able to find out the vac applied pressure untill the engine is running. So I may start with the injector flow set for what they are with no vac on the fpr. I one thing I found out while tuning (both the 7747, and the 7427) is my engine likes little fuel at idle, and lots at higher. Both times when I tuned from the stock chevy fuel maps, the low rpm cells I had to lower, and the higher rpm cells I had to raise.

On the stock lt1 fpr, is the pressure simply one pressure when vac is applied, or does it vary based on how much vac is applied? Meaning at high vac, it might be X pressure, then at med vac, its XX pressure, then no vac its XXX pressure.
Diffrent engines have diffrent ammounts of vac at idle. I know my engine, best I can get at idle is around 49kpa. Just curious if there is a set ammount of pressure drop based on ammount of vac applied.

[EagleMark]

Remembering checking mine it was steady 43.5 PSI while checking under hood revving engine and only went up when I did a big opening of the throttle. So I beleive it's fairly steady till low vacuum.