Which fuel pump(s) for my 2.5 litre twin-plug ?

andyjboy · 05:47 AM

I am about to install a 2.5 litre twin-plug in my 911R-inspired ('72) car which previously had a high-compression 2.7RS-spec mfi engine.

The 2.5 engine is equipped with 40 IDA Webers & I will be installing new fuel pumps (in parallel) but don't know which particular model is most suitable.

I will be using Facet cylindrical pumps (which look very similar to the late '60's Bendix pumps) with a fuel pressure regulator & in-line pressure gauge - which of these 2 models would be most suitable ?

1) Model 476087 Silver top - 4.0-4.5 psi flow rate 18galls/hr

2) Model 476459 Silver top - 5.0-6.0 psi flow rate 27galls/hr

- or do I need a higher rated (red or blue top) version ?

What diameter fuel hose should I be using - 6 or 8mm id ?

.

304065 · 09-28-2007, 06:05 AM

Andy,

About 3.5 psi should be just right for the Webers. Any more than that it just gets taken up by the pressure regulator. Too much and it's not good for the needle and seat but you know that.

The modern Facet pumps are a good near substitute. You can remove the yellow chromate conversion coating with oven cleaner and slap on a repro decal.

It's the fittings that are problematic, the modern ones use 1/8" NPT, a tapered pipe thread. The originals used a M12x1.5 banjo fitting which is incompatible with the tapered thread. I would use some 1/8"NPT to -6AN Aeroquip fittings for a modern car.

You can get black Kevlar braided hose in -6AN, this is much more old-school looking than the braided stainless. With a little searching the adapters can be found in silver or black instead of blue anodize. Overkill for 4PSI but can be disassembled, and compatible with -6AN fittings on PMO fuel bars, which should replace the old banjo fittings.

If you just want to go with barb fittings, the original hose should be:

COHLINE 251.0600 22 7.5x12.5 >NBR< - 25/98 DIN 73379 8'

Here is how the original was done, this is an Ernie Wilberg photo of 11899011R.

Another Ernie Wilberg photo.

For a regulator consider the Malpassi filter king, it includes a regulator, filter and a pressure gauge. Should be widely available on your side of the pond.

pieterk · 09-28-2007, 06:16 AM

John, since Andy's R-inspired car seems to hew closely to what I'm going to dive in to, is the fuel pump/regulator solution you guys are talking about the most common application for a 2.2-2.8 twin plug Weber carbed motor? What are the alternatives?

If the Facets can be cosmetically modified to look the Bendix's, then that would be great. Although my motor won't be a 2.0R, I'd still like the engine bay and all motor support systems to remain roughly faithful.

304065 · 09-28-2007, 06:32 AM

Pieter, if originality is not an issue, the right thing to do is to run a "modern" return-style fuel system as opposed to the "dead-head" type, with a high-capacity in-tank pump and a good fuel pressure regulator.

This is what I use with the ATL fuel cell in my 2,2E race car-- a Walbro pump inside the tank for good pickup under high-g conditions, feeding '6AN line to the filter console, then the return line from the filter console back to the tank. This keeps the fuel cool and helps prevent vapor lock and is in fact what the factory did in '69.

Fuel pumps are better at PUSHING fuel than PULLING it, hence the in-tank pump. The best part is, the pumps are $140 or so, originally came standard on the Eclipse/Talon cars so any FLAPS can come up with one in a pinch, but I carry a spare they are so cheap. A good fuel pressure regulator is a must with this setup, because you must reduce down the high pressure of the in-tank pump to a level usable by the carbs.

RoninLB actually uses two pressure regulators to get the pressure exactly right for his trick PMO setup.

For racing purposes, this is a better alternative due to the g-loads experienced. Grady Clay posted that a modern solid-state pump can be installed on the front crossmember by the tank and an old-school Bendix fitted, so that the fuel just flows through the Bendix but it doesn't pump. A clever fix, and if Grady were typing this he'd say be careful working with Gasoline, it's toxic and can kill you.

pieterk · 09-28-2007, 06:49 AM

Thanks John.

That was an easy sell on the more modern solution.

If RoninLB's regulators are in series, then is the second one set up with only a minute amount of reduction or are they both set to approximately whatever the specified pressure is, i.e., 3.5psi?

For this setup, would you still recommend the Malpassi Filter King? Or is something else better suited?

I like Grady's idea a lot. But then, if the Bendix copies would only be there for appearance and spirit, I'm seeing that as dead weight, which means I wouldn't need them.

cgarr · cgarr's Garage

This carter 4070 pump is nice for this application, just make sure you put in a crash safety switch in line, old junk fords have them.

http://www.racetep.com/webfuelspark.html

chris_seven · 09-28-2007, 07:38 AM

Andy,

Red Tops are the normal 'issue' and we have used them for quite a number of years.

I think that the only differences between the pumps if due to the internal filters and Blue and Red are the least restrictive.

There is an old calculation for pumps when used with restrictors BHP x 0.23 gives the flow rate needed in US gallons/hr and 0.17 as a factor when used with a spill return regulator

I always use a pressure reg set at 2.0 psi with a Weber.

The flow rates quoted are into an 'open' tank. They will deliver zero flow at 6.0 psi.

The Red Tops will provide around 35 gallons - (US gallons) an hour at 2.0 psi and when in good new condition pressure can be as high as 7.5 psi.

The 85mm metal bowl filter king has a tapping to a pressure gauge.

I always worry about connecting fuel pumps in parallel as I am not sure that the flows between pumps will balance. The stronger pump will always lead and do most of the work. Possibly not a problem in practice.

The location of the pumps in the 911R is not ideal as Red Tops and Blue tops work best when pushing rather than pulling and they are quite high compared to tank level, but I would mount them in this location jsut for appearance.

I would certainly use an 8mm ID fuel line as a 6mm could be a bit small depending on how you are connecting the pumps.

I am not sure about plumbing them in parallel as they may not share load equally and one may lead but maybe this isn't a problem in practice.

The other issue about parallel mounting is the size of the fuel lines and the flow capability of the pressure regulator. I have seen a 240Z with triple 48 DCOEs using a single Purolator glass bodied filter and adjustable regulator which suffered fro fuel starvation on long straights as the pipes and regs just couldn't deal with the flow.

I think PMO have two regs for this reason.

I have thought about piping a single pump to each bank of carbs being fed from a large diameter fuel line and then installing splill returns to prevent fuel in the engine bay lines from heating.

On our rally car sometimes we queue at a start line for 5-10 minutes and I imagine that there will be some fuel heating.

If originality isn't an issue Holley make a great rotary vane pump with an integral regulator that is very good.

andyjboy · 09-29-2007, 07:16 AM

Thanks for the replies so far guys.

I am keen to keep the installation looking 'period' & have some repro Bendix fuel pump decals (in German) on their way.

As I mentioned in my original post, I will be using 2 Facet cylindrical pumps mounted as in Ernie W's picture & using the correct-style fabric overbraided fuel hose - probably connected via the brass 'elbow' unions supplied with the pumps (although I may get some NPTF:metric custom addapters made up so that I can use original-type banjo connections) but will probably modify the layout to include a 'circulation' system (as often recommended by Grady Clay) since I still have the mfi return line to the tank.

Any comments from owners already running such a twin-plug set-up on the road ?

bob barnes · 10-01-2007, 06:50 PM

Guys,
Sure seems like overkill on plumbing these carbs. I had my 2.4L twin-plug ST clone using one Holley Red pump installed up front in the heater well and fed with no. 6 braided to a earls fuel in line filter and then to a holley regulator in the engine compartment. Branch off the regulator to each bank of 46IDA's. Also had a Fram competition filter between the fuel cell and pump. The 46ida's were replaced with 50PMO's for the 3.4l twin-plug and worked well until I just converted to FI. Before the holley, the Stewart warner pump with filter was used(1972-1995).

Bob

Eagledriver · 10-01-2007, 07:58 PM

You could just keep your original MFI pump. That's what I did. You just put a regulator between the pump and the carbs. I ran a loop of fuel line from the fuel filter consol just like the loop to the MFI system and then used a T fitting to tap fuel from the loop through the regulator and to the carbs. Works great and you still get the nice big filter as well as a return system. You can even use the cold start enrichment solinoid if you want for quick cold weather starts.

-Andy