Dual Webers: what low-pressure fuel pump?

Hi, guys.

Looks like the race engine is finally ready. The M102 Cosworth engine has been rebuilt to stock specs, except for cams and associated hardware.

The car originally came with horrid CIS/KJet fuel injection. That's being switched over to dual Weber DCOS/P 48's on a DTM manifold:

Here's a photo of how it should look when installed ... for inspiration:

I've got to figure out what to do with the fuel situation. Is a low-pressure fuel pump sufficient? If so, which pump do you recommend?

Should I also add an adjustable fuel pressure regulator? Or should I keep the stock high-pressure fuel pumps and just reply on an FPR to keep the engine from flooding?

Please help a n00b out!!

I used a simple electric pump and regulator that I picked up at Autozone. It worked pretty well for the 10 or so years I used it. I believe pressure ended up around 3 psi if I remember correctly.

Yep, quite low. I believe DCOEs, maybe the others, require no more than 5 psi

I'd go with the existing pumps and a double regulator arrangement, a bypass regulator running at 6psi or so, and that feeds a standard carb-type regulator running at whatever the carbs like. The Bosch fuel pumps used in anything CIS kick ass and it would be silly to take them out.

I like that idea as the dual Bosch pumps in my car are brand new.

What pressure do you need for Webers? I'm totally new to the carb world.

a good rule of thumb is that the average carb needs about 5 psi i fuel pressure, i'd start there and adjust if needed

3-4 PSI is what DCOE's work well at. Any fluctuation in pressure will mess with your tune.

I think the K jet pumps are way too much. Using an expensive regulator to bring 90+ psi down to 3 seems silly when there are a huge selection of high quality pumps out there.

Every vintage racer I deal with just uses cheap Facet parts store pumps with a spare on the trailer in case it is needed.

Is pressure the only variable? Isn't flow also an issue?

Facet pumps work well

Facet is the brand I used, and I never changed it in ten years. I experimented with the pressure, but my Webers never ran well on anything but 3 psi. They are sensitive to the pressure. I'm with others, I think using the high pressure pumps and regulating them will eventually cause other issues and seems like making a simple process difficult.

+1 for the Facet and regulated to 3-3.5 psi. Webers work best in this range.

LanEvo wrote: Is pressure the only variable? Isn't flow also an issue?

Pressure is just restriction to flow. If you clamp the outlet shut, the pump will run right on up to whatever it stalls at, either from an internal bypass or just mechanical limits.

The CIS pumps have a very very high max pressure. They are also extremely overbuilt as far as pump design and motor durability are concerned. Regulated down to 10psi or so, they are no different than any other pump.

I like the idea of having a bypass regulator and a second, low pressure regulator because it will result in the most rock-solid and steady fuel pressure possible. Carbs like that. As a bonus, you already have the billy bad-ass pumps, all you need is a $80ish bypass regulator and a $50ish 1-4psi Holley regulator. No need to buy a silly-expensive Facet pump, which is little different from the $40 rattlebox junk pumps you can buy at Autozone.

Check out the webz for user experience with the cheap low pressure regulators from Holley, etc.

I've used a Carter 4070 rotary pump on my dual Weber 2002 for many years. No regulator needed, as it's a high volume low pressure pump.

I was looking at Aeromotive. Any good?

Also, what do I do about fuel return?

Don't know about the others, but no return is necessary on the Carter I mentioned.

No return is needed with the Webers.

He'll want a bypass regulator, which means he'll have a return. You can just run it back to the tank.

I run a Holly Blue in my RX7 to ensure I'll never have a delivery issue. It's 110gph open flow.

erohslc wrote: Check out the webz for user experience with the cheap low pressure regulators from Holley, etc.

I went a very long time with one, because Nikki 4-barrel carbs like about 1.5psi fuel pressure. Never any issues.

I guess the question is: do I need a fuel return at all?

Like I said before, NO.

You need a return if you keep your existing fuel pump, because it will require a bypass type regulator. If you ditch those and get a carb pump (low max pressure) then you won't.

Since it's a track car mostly, a return line with a bypass regulator is a very good idea to avoid fuel heating. It's cheap insurance.

When we ran triple Webers on a TR6, they really didn't like going over 4 PSI of pressure. We ran ours at 3.5 PSI with a Holley red pump and a pressure regulator with a gauge. If you already have a return line, it sounds like the bypass regulator would do the trick.

As far as flow goes, you can definitely have too little. We had a small backup pump in-line under the hood, and it couldn't keep up with 3 Weber 40 DCOEs at full tilt.