Looks like option 1 wouldn't have full control over fuel pressure to the engine, since it could bypass the FPR completely causing irratic pressures or flow issues. If I think of a ball valve tee'd on a garden hose with some distance between the Tee and the valve, open the ball valve to releave pressure and flow out the end of the hose would compensate but with no doubt some delay in pressure and flow. Option 2 has the FPR inline with full control over the fuel flow as the fuel has no choice but to go through it to get to the motor. I would go with option 2, if you get a decent regulator you should literally have NO restriction anyway. Even the $160 bypass style aeromotives flow more fuel than a 450 can put out at the higher pressures (the ball on the diaphram is like almost 1/2" in DIA) which is what seals the bypass port. That ball is HUGE for a EFI style regulator bc it serves dual purpose as EFI and CARB so it has to be able to bypass the high flow low pressure in a carb system.

 

six of one, half a dozen of the other. Really wont matter either way, unless the chosen reg is a very poor design that might impede flow through it.

But as said before....at a push, you're low boost, just ignore the boost reference. Stick the new reg either near the tank, or in the tank and contain everything there.

Although in tank will make adjusting a little more awkward. But as it's low boost, you could just run a static 60, 70psi or whatever.

Although the boost reference does make it more versatile and future proof, so would be preferred.

 

I'm thinking the boost reference may help compensate for my dropping fuel pressure that I'm seeing currently under boost. Seems like there are only 2 options as to why that's happening ......the walbro 450 isn't putting out or has a leak in the feed hose (which was changed), or the stock regulator is being flaky and doesn't know what to do with so much fuel and can't compensate (obviously) under boost.

With the Black Friday sale I picked up a Racetronix FPR that looks good and was like $68 plus shipping, good deal. I can start with option 1 and if I don't like the result always switch to option 2 pretty easily.

 

I guess a question would be what is considered "low boost"?
I use a 255 on the stock system with 80 lb. injectors and a second 255 on a Hobbs comes on at 4 psi. to provide additional fueling, no regulator other than whats in the tank.
Been trying to figure out when an adjustable fuel pressure regulator would be needed, probably when the entire fuel system gets upgraded.

 

I think Racetronix website still has their sale. $75 for a good boost referenced FPR is a good deal.

 

I classify anything below 6psi as low boost. Something like 4psi technically wouldn't even require any timing changes or insane fueling changes if any as long as you dont run out of injector. Also anything below 6psi is less likely to pop a piston if your a little lean.

 

Im at 10 currently and planning on hopefully 15 if the rear mount can make enough steam. 93 octane only.

 

I dunno Spider, I'm at 13 lbs. on the current setup, pump fuel only.
Been that way for years now so technically I should be looking at this lol.

 

I wasn't swaying you 1 way or the other, just saying that I was at 10, trying to move to 15 and adding this regulator. If you plan to get 1, Racetronix has a good deal going right now. I will obviously report back when I add mine and can state how steady the fuel pressure is after doing this mod. If I get it sorted and get to 15 psi, I may also consider a meth kit as well.

 

It's a variable. Say if you ran a flat 65psi fuel pressure. Then really I wouldnt be overly bothered running say 20psi boost on an appropriately setup non boost referenced system with adequate injector, as it's still leaving a solid 45psi pressure across the injector. And 65psi base isnt overly taxing anything on the fuel system run all the time.
Although I probably wouldnt want to be running much more than that, but there's no real reason you couldnt run say 75psi base, in which case even 30psi boost wouldnt be a trouble to the fuel system, again assuming flow/pressure/injector are all adequate.

But boost referencing is the preferred way of doing it.

 

All of gms stuff since the mid 2000s are feed through or some type of odd feedback and arent an issue. Even the regular fbody isnt anywhere close to traditional style.
As long as you keep restrictions to a minimum there should not be an issue.

 

Statement- I'm noticing a drop in base fuel pressure after the car is warmed up and driven for a half hour or so. I cleaned up all the wiring and added a true external boost referenced FPR and bypassed the stock in tank one. Single 450 with a hot wire kit. I had set base pressure on a cold engine with the vacuum line removed to 58 psi. It dropped to ~50 once the vacuum line was reconnected as expected. I noticed in a log after much stop and go driving that my base pressure was down in the 30's.

Question- Do you typically set based pressure after everything is up to temp and warm or it shouldn't matter? Seems very odd unless I'm heating the fuel too much.

 

A drop from 50 to the 30's sounds massive.

I live in a cold climate, so temperature has never really been a concern. Occasionally I have driven in traffic, in very hot weather ( for me ), but even with those extremes, I've only seem small deviations in pressure. Never as much as that

Even with external 044's running, on occasion yes they would audibly change, their actual performance didnt seem affected.

But fuel temperatures with a running engine would never change dramatically. Would need to review logs ( many years worth however... ) but fro memory, highest running fuel temp I've ever seen is around 120DegF
But most typically it's around 80-85degF.

Ambients here would be 50-70degF, with max encountered above say 85F or so.

Generally I set my base pressure ( I use relative FP on my ecu ) with vac line connected, engine running etc etc. relFP is basically FP-MAP so should remain a constant throughout the engines running and at present this is around 3200mBar. ( Same odds as setting base with vac disconnected though ). At very high load it does drop to around 3000mBar. But that's like only a 3psi drop.
That's with a pair of 450's PWM'd running all the time, Edelbrock FPR

Pressure did fluctuate more than this with the 044's years ago, but not as much as you're experiencing. But although it did drop a little under load, it was always totally consistent and repeatable.

If you're dropping at no load....that is a concern. Log fuel temperature if you can, just to see ?

 

I'm beginning to wonder if this 450 is just messed up from the beginning. I redid everything this time. New feed line, cleaned up wiring, removed the 2nd pump, bypassed the return reg, new external FPR, etc. Only constant has been the 450. I guess I could always put the 255 back in and see if cruising drops FP slowly.

I'm following Greg Banishs info for setting up the FOR with his injector data and he has the vacuum disconnected engine running when setting base pressure. Either way it seems awfully odd to drop that much over some cycle time.

On the plus side my MAF curve actually looks reasonable now that fuel pressure increases with boost. That said I'll have to redo it when I sort out this pressure drop issue 😠

 

If you think it's maybe runtime or something causing the pump woes....

Set the pump to run all the time ( engine off ) and record pressure over time, with no other external influences involved ( big battery however )

I did that a few years ago with the 044's to dispel the nonsense of people claiming running 2 pumps heat the fuel up like ****. Fuel temp did rise a little...but only a little over a 20 minute test with both 044's running at 60psi test pressure.

But yes, chucking a 255 in there is another option to test.

 

Good thought! Since adding the hot wire kit that's actually a very easy test to jump the relay to the pump and keep a charger hooked up to the battery and let it run. Will try that today and update. Easier than swapping pumps even though I have a trap door to the tank.

 

Where did you buy the pump from? I have heard of fake 450s being sold from amazon/ebay.

 

Verify pump supply pressure to reg isn't dropping to 30. If it is, pump issue. If not, reg issue.

 

It was an Amazon but I went through the reviews first where enough people said it work well that i trusted it. Had all the right stampings on the pump too.

 

How the heck do I do that without changing the entire fuel system output to get a gauge on it?