Barwick

I've got a fuel cell on the way for my '80 RX-7 SCCA ITA car, and obviously the carb only needs a couple of PSI. However the fuel pump in the fuel cell pumps at like 80 psi the guy said. I don't know jack about fuel systems, so someone help me out?

Either I'd like to regulate that pump to only run at the required PSI, or restrict it somehow so that it only ends up like 80 psi before restriction, and like 7 or whatever after.

Either way, it's GOT to pump enough fuel at enough pressure at higher RPM ranges too.

WackyRotary

That sounds like a annoying problem. I'm sure theres a way to get the PSI you want but would be simplier to have Carter or Holley fuel pump instead you know.

Barwick

how much do those run? and can I fit 'em into the fuel cell?

RXcetera

80psi? lol! If you're running a carb, you'll probably need 3-7psi at the most. That's the wrong kind of pump for your application... regulating 80psi down to 7 will be a high pressure nightmare waiting to happen and will kill your pump pretty quick. Make sure you arent confusing GPH (gallons per hour) with PSI... or buy the FI unit that pump was meant to be used with in the first place lol.

WackyRotary

I got my 95GPH holley fuel pump for $80. A carter 75GPH is like $70. They both run near 7psi, you will need a regulater too.

rotorhead

you could regulate it down, and i'd definitely go with metal fuel lines. but like rxcetera said, you'll be looking at some probs later anyway. i think the carter was like $140 or so. check summit racing for carter afb carbs, holley blue carb, or even holley red(like mine). the red has a bit more output....nowhere close to 80 psi tho'!:p

mar3

iTrader: (8)

Find out from the tank supplier if the pump will tolerate operating at a lower voltage (thus lower line pressures) and if it can, have your favorite local electrician rig up a box to quarter your input voltage to the pump. You'll be at apprx 20 psi and a good regulator along with your return line should keep the unit from stressing out. Plus side is that you can later pull the box and you're ready for FI without having to pull the tank or rework your fuel supply system.

Sleeper

rising rate fuel regulator

Barwick

it's going on a race car (that's why it's a fuel cell), and I'm not about to buy another carb, besides, the one I've got was built for ITA anyhow. Does anyone have any experience with fuel cells? Think I can put a regular fuel pump into the slot on the top of the cell where the current fuel pump is at?

peejay

I think you should be fine if you do some smart tuning.

Here's why I feel this way... fuel pumps do not supply pressure, they only supply a volume! Need proof? Tee a fuel pressure gauge into a fuel line, but don't put anything on the outlet of the tee. Turn the fuel pump on. How much pressure does it generate - nothing! It's only supplying a volume, in this case it's supplying the volume all over the shop floor.

Hmm... let's cap off the end of that tee so we don't start swimming in Shell's finest. Now the pressure gauge is reading something. So what makes pressure?... resistance to flow!

Let's back up a bit... why did he call it a 80+psi fuel pump? I don't know either, given that fuel pumps don't make pressure. Maybe the fuel pump is rated to be able to supply fuel at UP TO 80psi? You see, a fuel pump can supply more volume at lower pressure (like just an open hose dumping it on the floor) and the amount of fuel it can supply tapers off as you increase resistance to flow, and therefore pressure. Like with our tee capped off... in that case we have zero flow.

So knowing this, what can we do? What I would do would be to run two regulators in series, the first set to 9psi or so, the second to whatever fuel pressure you want to run at your carb. Better yet, run a fuel return style setup before the regulator like our cars had from the factory so that the pump doesn't kill itself or your fuel lines trying to cram all that volume into what is basically a closed pipe when you're at idle. It'll take some tinkering with the restrictor in the return line so that you don't run out of volume at the top end, but it can be done. (A little birdie tells me to start at a .050-.075" orifice)

setzep

I like the way peejay thinks!

I've been thinking about the same thing for my buddies camaro. The car has a intank pump that is meant for the FI V-6 that came with the car but he's putting in a carbed V-8. At first I was thinking of using the orifice idea like peejay said but now I'm thinking of using a check valve. I'd run the supply line into a tee, one side of the tee goes to the carb and the other side goes to the check valve, from the check it would go back to tank via return line. The valves that I have are 3, 5 and a 10 psi (meaning that it takes that much pressure to crack the check open going through it in the freeflow direction). I think I'm going to start off with the 3psi at first and see how much pressure I get at the carb, i figure it will build some additional pressure to move the fuel back to tank. If that doesn't supply the 7-9 psi that we are looking for I'll toss in the 5psi check and see where that gets us.

My other friend with a V-8 in his FC is just using a cheep $20 FPR that regulates downstreem pressure of the regulator to 7psi and deadheads the fuel pump, not good for the pump!

Good luck!

Cam

peejay

right! you don't want to dead-head (run w.no return line) a pump that doesn't have an internal regulator. FI pumps generally do not have internal regulators, they have one built in to the fuel rail or just after it. The regulator bleeds off pressure (varies its resistance to flow) after the fuel injectors, maintaining a constant PSI at the injectors.

You CAN dead-head a pump with an internal regulator... that's how WT's system worked. Net wisdom maintained that you needed a huge fuel pump to maintain pressure at the high end, I looked at the system and realized "why do I need a return line? the fuel pump I'm using wasn't designed to have one!" and there I go, no need for $80 Holley fuel pump. You always ALWAYS need to run a regulator before the carb, though, so that you can adjust fuel pressure down as you see fit. (When drag racin' I ran about 5-6psi into the Nikki! No lie! Any less and it'd run lean over 6500... too cheap to buy new jets so I just cranked up the pressure It never overpowered the float either...)