twin fuel pump question

[advtracing]

with the change over to webers and the car heading towards more a factory race / rs i am tempted to continue with the addition of twin fuel pumps and mounts in the front trunk next to the smugglers box.
So which fual pumps give the correct look and flow for webers and has anyone got the the basic connection diagram of pipes and how they join the tunnel feeds.

[chris_seven]

John,

It was common practice on Rally cars for many years to fit Twin Fuel Pumps because of reliability issues with Bendix (Facet) Red Top Pumps.

Back in the early Seventies when we first started using these pumps they were commonly installed in Escorts flat on the boot floor and they did, indeed, regulalry fail. I am sure that this was due to manufacturing issues and the mounting arrangement.

They used to be simply piped in parallel and then individually switched through relays so only one pump was electrically connected at any one time. It was also possible to turn off both pumps.

The number of times pumps have been switched off mid-stage with the subsequent time penalty is bewildering and I fail to understand why this should happen but it does.

I have also seen pumps connected in parallel and wired so both work together and then one pump will tend to lead and the other will tend to lag as they rarely have a balanced output - particularly into a pressure regulator.

In recent years I have tende to use a single pump mounted vertically - as recommended - and have had no issues with failure. It simplifies the entire installation from both plumbing and wiring.

We haven't retired from an event due to fuel pump failure for more than 15 years but we have changed car every 5 years and always start with a new Red Top Facet Pump.

We also change one of the internal springs in the pump so its maximum pressure capability is reduced form 6-7 psi to 2.5 - 3 psi.

A single pumps delivers at least enough fuel for a 270BHP Twin Plug on 46IDAs.

I am sure most people will disagree but I just don't like carting around too much weight and too many pipes.

[John Z Goriup]

Even though I'm not able to answer your questions about line routings and other specific details, but I can offer some photos of various twin-pump installations I've seen over the years on Porsches with a wide variety of intake systems:

1.Ed Palmer's 2.5 liter Weber-carburated SWB 911 with his own installation.

2. '74 RSR with twin-pump set-up feeding slide-throttle MFI injected 3.0 liter

3 & 4. Brumos built 2.2-liter, IMSA championship-winning '70 911S

5. a pristine, factory original yellow '73 MFI RSR

[John Z Goriup]

and as final examples:

6. the ex-Fittipaldi IROC RSR with twin pumps feeding the 3.0 liter slide-throttle MFI engine.

7. the 2.0 liter Larrousse R with engine-comparetment mounted twin-Bendix pumps feeding a set of Webers.

[72Group4]

Does anyone know what type of switch was used to control the twin pumps and where the switch was located on the factory cars? If you have can post a picture that would be appreciated.

Andrew

[mike curnow]

On the RSR there was no switch, both pumps ran all the time. On another subject, I have often wondered how they worked on the RSR. The RSR pumps, just like the street MFI pumps are not rubber diaphram pumps. They work with a steel roller, like a roller bearing. In street cars they are located lower or level with the tank output, in the RSR they are basically above the whole tank, which means when the tank is say half empty they have to pull a head of about 12 to 15 inches. I thought a steel roller pump would be a pusher pump, not a suction pump?

[72Group4]

Raj,

So were both fuel pumps always on for the smaller displacement 2.3 - 2.5 litre Group 4 cars just as they were on the RSR?


A

[Flunder]

Wow,i am not sure when twin pumps were first used...Will have to ask others here for their opinion as well.We would have to start with 70,71ST's.
.

The MY1971 Werks built Safari STs had twin mfi pumps located just as in the later RSR.See Werkfoto post 505 page 51 Another Hot Rod.

[72Group4]

On the Werks built Safari STs were both pumps always on or were they switched (Off/Pump 1/Pump 2)? I believe the flow requirements of the 2.3 - 2.5 litre cars can be met by one pump - using one means less wear and tear on the spare pump but not an instantaneous switchover in the case of failure. Also wondering what the period privateer cars did here?

[advtracing]

Continuing the discussion on this , when we had st's running Weber setups would they have had twin pumps and if so which Bosch pumps ate period correct.