Rauq

iTrader: (1)

I'm plumbing my own return setup on a swap car- 1984 Mazda RX-7 with an LM7. I've got two screw pumps, one will be on a hobbs switch. This is what my general layout looks like:

click here, image won't resize

Because of the slight vacuum on the return line (which will actually go pre-filter to reduce vacuum) I'll have to bump up the pressure on the regulator a little (58 psi is usually assuming 0 psi on the return line, or even a slight positive pressure, so "62psi" on the regulator will actually be ~58 with 4psi vacuum on the return line)

The fuel cell has two -8 AN fittings for feed. I was just going to run -8 AN everywhere for simplicity's sake.

However... my Summit Racing cart has $75 worth of fittings alone in it. Is there any cheaper option for fittings anywhere?

ss performance

iTrader: (17)

I would run the return back to the fuel cell. I am not familure with running the return back to the supply to one of the pumps, but it seems to me this could cause problems with the regulator. I would feed one pump to each fuel rail tee them togeather to keep them equal then from the rails to the regulator.

Good luck.

Rauq

iTrader: (1)

I'm running stock truck rails with a boost referenced regulator, and I'd like to keep that the way it is. These pumps flow too much (330 lph @ 58 psi) to have them both on all the time. Returning into the feed line prevents the fuel still in the cell from heating up, and reduces plumbing (my cell has 2 feed lines and a vent).

In theory, the fuel pressure regulator functions off a 58 psi difference (+/- boost reference). <58 psi at the rails = no return, >58psi at the rails = return- but all of that is assuming 0 psi on the return line (or maybe a slight positive pressure from pushing the fuel back through the return line). Put a restriction in the return line, and you increase pressure in the rails- 4psi restriction should put 62psi in to the rails. Conversely, with a vacuum on the return line- say 4psi worth, I would imagine that's going to put fuel rail pressure at 54psi.

ss performance

iTrader: (17)

My concern would be that the pump would pull too much from the return side and cause fuel pressure problems.

mjollnir

Never done this but with your routing I can see it will suck air from the return line once it empties it! And you'll inject air in your cylinders. I would plug the return line to the tank.

Lonnies Performance

iTrader: (16)

I wont suck air... there is no air in the return line. Return lines bleed off excess fuel/pressure.

The problem is that the fuel will get hot as it will constantly recirculate through the return line back into the pump. Do not do this, it will cause you problems with pump overheating & cavitation.

Rauq

iTrader: (1)

That's the problem I was intending on addressing anyway- fuel that's made 1 pass through the rails and been heated up getting dumped back into the tank, warming all the fuel in the tank.

I will run the return into a T between the fuel cell and filter. I'll probably try going into the feed for the always-on pump first, and if that doesn't work out I'll switch it over to the hobbs-switched pump.

Hey Lonnies, (Is your name Lonnie?) have you had any experience with the new Walbro/TI screw pump, WSP330? The Supra guys call them a Pierburg 800, but either way, there's not a lot of info out there from users.

Rauq

iTrader: (1)

Also... 8mm barb outlet on the pump is stupid. Barb inlet & outlet is stupid as well, but 8mm barb outlet is especially stupid.

EFI hose clamps?

ss performance

iTrader: (17)

Roug

Your logic is faulty. Yes the fuel gets heated in the rails. If you circulated the fuel from the rails back to the pump you are heating the fuel going through the pump which again passes through the rail gaining even more heat to once again be recirculated to the pump heating that fuel even more to pass again through the rail etc etc etc.

The pump pulling fuel from the regulator will cause the regualtor to have problems, if you place a restriction in the return line to prevent this then you will have back pressure on the regulator causing fuel pressure problems. You can't have a closed loop system with a pump, as Lonnie stated this would cause cavitation which airiates the fuel which causes all kinds of problems.

The hot fuel being returned to the tank would allow that fuel mix with the cooler fuel in the tank, cooling it, before it is once again run thru the tank.

You posted asking peoples opinion of what you are planning. Not one person has thought it is a good idea but it seems you are determined to do it your way. Did you post this looking for information of validation.

Rauq

iTrader: (1)

I understand that running the return into the feed will result in higher fuel temps due to the higher concentration of fuel in the rails that has already been through the rails before and due to going through the pump multiple times. But nothing has been said regarding lower fuel temps in the tank running it that way. I would think that eventually fuel temps in the tank would rise enough to negate the return/feed setup (especially considered I'm running only a 12 gal cell, not an 18 gallon tank with a greater surface area), although you guys have convinced me enough that I'm not going to permanently set up my fuel system to run the way I've got going in my mind.

I addressed the regulator- it's a diaphragm type with adjustable pressure, and raising the pressure setting of the regulator would compensate for any vacuum on the return line. Adding a slight restriction on the return line would also negate any effects that a slight vacuum on that line would have.

Gonoma

iTrader: (15)

Ok why are you worried about the temp of the fuel in your tank? Your tank temps won't do you a bit of good with the way you have your system plumbed...you might as well be running a 1gal cell. Its best to just do it right the first time. Just buy a bulk head fitting and install it in the cell for the return if you can

Lonnies Performance

iTrader: (16)

good luck... you'll need it.