Mechanical fuel pump limit

[promotor]

At what engine spec do you guys think it is a good idea to fit an electric fuel pump?

I'm not a fan of the electric fuel pumps and I think that the mechanical pump could still easily supply enough fuel for a road car (max 6500rpm) with approx 150bhp.

Any experience here with good and bad stories of mechanical and electric fuel pumps?

[nmauduit]

I would suppose this is not for racing (where one would opt for ruling out uncertainty), and I believe LTC mechanichal pump may vary in the maximum flow they are producing (depending on throw / gasket thickness, membrane actuator ring size etc ...), so once the engine is set and tuned I would install a fuel pressure gauge at the carbs and check that the pressure does not drop to zero when at full revs. This can be achieved cheaply by tapping a spare Weber inlet filter plug so that is can accomodate a small pressure gauge:


https://lotuselan.net/forums/viewtopic.php?f=40&t=46956

[JonB]

The benefit of an electric fuel pump is reduced cranking prior to start, which you need to do in order to fill the float bowls of Webber and Dellorto carbs, especially after any short lay up. When you park up, the fuel in the float bowls evaporates, as they are open to atmosphere. Takes about a week when it’s warm.

Not sure if this affects Strombergs.

(Edit: viewtopic.php?f=39&t=14220 is pertinent.)

Anyway, FWIW I fitted a Huco low pressure pump to my Plus 2 and it make a real difference to cold starts. Couldn’t hear it either, once started. It’s made for carbs and needs no pressure regulator.

[elans3]

Agree with the above. I have fitted a Mitsuba FP3 pump to most of my Twincams (both Alfa & Lotus,) and the main benefit is no churning over as above, and when coupled with electronic ignition (123 distributor on the Alfas, & Aldon Ignitor on the Loti), means instant starting. Wouldn't go back to a mech pump.

[webbslinger]

I agree with the last 2 posts regarding ease of starting with an electrical pump. As for reliability, I carry a spare complete with fittings in the car.
The reason I switche'd to electric though is primarily because of the nearly inaccessible location of the mechanical pump. I can swap an electric one in minutes beside the road, but just getting to the mechanical one is a nightmare.

[2cams70]

The flow rate limit of the mechanical fuel pump would be largely governed by the diameter of the diaphragm and roughly speaking fuel flow rate requirements of any engine is dependant on the HP rating. As far as I know there was only one available diaphragm diameter for the AC glass bowl fuel pumps.

Here in Australia the AC glass bowl fuel pump was still standard fitment on the 3.3L 6 cylinder Holden LJ Torana XU1 engine developed for racing. It had a 190HP rating.

I'd suggest therefore that the AC fuel pump has quite a bit in reserve insofar as flow rate is concerned. The limitation may be the maximum RPM it can reliably operate at.

https://www.tradeuniquecars.com.au/feat ... r-turns-50

[StressCraxx]

I have a mechanical pump on mine. If the car sets for a week, I crank the engine without pumping the pedal until I see the oil pressure come off the peg. Then I give it about 5 to 6 pumps and crank it over again. Starts right up.

I have had several Fact "cube" pumps. They are great until they are not. The best electric one I had was a little Mitsubishi rotary fuel pump that made 2.5PSIG and never had an issue until it started to weep from the case.

[Foxie]

When I first got my Plus 2 many many years ago I had a few problems with the mechanical pump. Problems were difficult to diagnose as the engine would not start to make the usual checks, and worse if you were stopped on the side of the road it was a big problem to access.

After reading up on an electric conversion ( like you are doing here ! ) I bought TWO electric Facet pumps over 20 years ago. The first one is still running, and never failed.

I have it mounted in the boot. I have a Facet Filter King on the front bulkhead which I set up with a mini pressure gauge as seen in a previous post, and a relay operated by the oil pressure light to as a safety cut out, ( the only good thing about the mechanical pump imho )

[2cams70]

The old original AC mechanical fuel pump was extremely reliable back in the day and used in millions of vehicles of varying makes and models. Whether it is still reliable today due to fuel spec changes, poorly remanufactured service parts and meddling by incompetent people not knowing what they doing I am unable to say.

[alanr]

Re- Mechanical pump from the point of view of starting.
I have found that since I fitted a Hi-torque starter motor that turns the engine over much faster any thoughts of fitting an electric fuel pump are now completely gone because the engine now starts quite quickly even after not starting the engine for a few weeks.
What the rpm limits of the mechanical pump are though I have no knowledge.

Alan

[gjz30075]

I'm not a fan of the electric fuel pumps and I think that the mechanical pump could still easily supply enough fuel for a road car (max 6500rpm) with approx 150bhp.

I agree. My 1720cc 150hp (flywheel) goes to 7k rpm without a problem with the stock mechanical
pump, but without an AFR gauge, I don't know for sure if it runs lean there. I don't think it is.

[rgh0]

Once I got my engines above 170 hp they started to run out of fuel at full power on the track and on the dyno due to the original fuel line being to small and the low pressure cylindrical facet pump not able to get the fuel to the engine fast enough. A mechanical pump sucking woulld have the same problem. A larger fuel line and better pump resolved the issue.

With 150 to 160 hp your probably Ok with the mechnical pump or typical low pressure electric pumps and original fuel line

cheers
Rohan

[gjz30075]

Rohan, are you still running the stock fuel tank? I'd imagine the choke point would be the metal pickup
tube within the tank.

[Craven]

Original AC pump fitted to the Twin Cam was an uprated version, seems to be expediently forgotten in the mist of time. Remember the pump is running at half engine speed and only makes pumping strokes when needed, self-regulating.

[2cams70]

Original AC pump fitted to the Twin Cam was an uprated version, seems to be expediently forgotten in the mist of time. Remember the pump is running at half engine speed and only makes pumping strokes when needed, self-regulating.

The original Lotus Twin cam pump is not an uprated version of the standard AC pump. The only difference between the Lotus Twin cam AC pump and the AC pump fitted to millions of standard Cortinas is the spring behind the diaphragm. This spring regulates the delivery pressure which is actually lower for the Lotus Twin Cam to suit the needle and seats and floats used in the Weber carburettors. Diaphragm is the same, everything else is the same and so therefore maximum flow rate is the same.