14 replies to this topic

[matthew_leech]

Posted 30 December 2012 - 09:45 PM
Right, looking for a little adice

The engine spec is

1293
Stage 3 head
Lcb + rc40
Sw5 cam and 1.5 roller rockers
Twin 1.5su's(abd needles and red springs)


Will the dry trusty and reliable fuel pump be suitable or will the facet fuel pump I already have (so at no expense) be a better option for me?



Thanks a lot,

Matt

[Sam Walters]

Youll be more that fine with a mechanical one.

[dklawson]

Unless you are running your engine for prolonged periods at full power (i.e. racing on a track) either pump will be more than capable of keeping up with the fuel demand.

[matthew_leech]

Excellent thank you guys!

I have only had my mini 2 years, and as a second car not doing much mileage, is there one which is more reliable or preferred??

[dklawson]

There are arguments for each type of pump. For simplicity, if you have a working mechanical pump, use it. If you are replacing a defective pump you could go either direction.

If you don't have an electric pump at the moment you will have to run wiring, bypass the mechanical pump, and fabricate a mount for the electric pump. It's not a lot of work but it is certainly more than replacing an existing mechanical pump with a new one. The only advantage I can think of for an electric pump is that you can turn on the ignition key and wait for it to fill the carb float bowl. That can be helpful if the car is not driven frequently. With a mechanical pump, if the float bowl is dry you have to crank the engine over on the starter to get the float bowl to fill. If the car is driven daily this is not an issue as the bowl will always be "full enough" for easy starting regardless of the pump type.

Then there is the issue of fuel pressure. A factory type mechanical pump will deliver the proper pressure (about 3 PSI) for the SU carb. There are electric SU pumps and they also deliver the correct pressure. However, many people who fit electric pumps choose an aftermarket brand. If that pump does not have the correct pressure rating you have to fit a pressure regulator in addition to the pump itself (more parts, more plumbing, more money).

The last consideration is cost. It has been a while since I bought any fuel pump but traditionally the electric pumps have cost a bit more than mechanical even before you factor in other items that you may want or need like the pressure regulator and an inertia or roll-over safety switch to stop the pump in an accident.

[MRA]

Electric fuel pumps must have a regulator fitted, this is to control the pressure difference caused by voltage surges.

I would never fit a mechanicalpump with an LCB simply for safety reasons..

[dklawson]

Being an electric pump does not automatically mean you need a pressure regulator. A stock SU electric pump does not require a regulator. If you choose the correct Facet pump (many are available) it won't either. On SUs there is no change in output pressure based on voltage, as a spring controls the discharge pressure (the electrics are used only on the "suction" stroke of the pump). Not all electrical pumps are constructed this way but I have never heard anyone mention voltage fluctuations affecting output pressure on other brands of electric fuel pumps.

Regardless of which pump you select, your goal is for a pump offering a discharge pressure close to 3 PSI (at least if you are using the stock SU carb).

[matthew_leech]

There are arguments for each type of pump. For simplicity, if you have a working mechanical pump, use it. If you are replacing a defective pump you could go either direction.

If you don't have an electric pump at the moment you will have to run wiring, bypass the mechanical pump, and fabricate a mount for the electric pump. It's not a lot of work but it is certainly more than replacing an existing mechanical pump with a new one. The only advantage I can think of for an electric pump is that you can turn on the ignition key and wait for it to fill the carb float bowl. That can be helpful if the car is not driven frequently. With a mechanical pump, if the float bowl is dry you have to crank the engine over on the starter to get the float bowl to fill. If the car is driven daily this is not an issue as the bowl will always be "full enough" for easy starting regardless of the pump type.

Then there is the issue of fuel pressure. A factory type mechanical pump will deliver the proper pressure (about 3 PSI) for the SU carb. There are electric SU pumps and they also deliver the correct pressure. However, many people who fit electric pumps choose an aftermarket brand. If that pump does not have the correct pressure rating you have to fit a pressure regulator in addition to the pump itself (more parts, more plumbing, more money).

The last consideration is cost. It has been a while since I bought any fuel pump but traditionally the electric pumps have cost a bit more than mechanical even before you factor in other items that you may want or need like the pressure regulator and an inertia or roll-over safety switch to stop the pump in an accident.

Thank you for spending the time to write this, it's for a new engine build so its all off the car, luckily in my dads vast spares, I have both a regulator amd a facet pump available for my use at no cost!

I think I will go for the electric pump, I will also be able to wire something up so the pump won't get power if you just jump in and start it up. With the amount of minis getting stolen I need to make it as hard to steal as possible!

[matthew_leech]

Electric fuel pumps must have a regulator fitted, this is to control the pressure difference caused by voltage surges.

I would never fit a mechanicalpump with an LCB simply for safety reasons..

I can see the logic in this, but there will be two carbs sat over the top of it anyway? Surely the carbs are much more likely to leak onto the manifold than the pump???

[MRA]

Being an electric pump does not automatically mean you need a pressure regulator. A stock SU electric pump does not require a regulator. If you choose the correct Facet pump (many are available) it won't either.

Sorry forgot about the good old SU Butec electric pumps... :-(

[MRA]

Electric fuel pumps must have a regulator fitted, this is to control the pressure difference caused by voltage surges.

I would never fit a mechanicalpump with an LCB simply for safety reasons..

I can see the logic in this, but there will be two carbs sat over the top of it anyway? Surely the carbs are much more likely to leak onto the manifold than the pump???

Any fuel leak is a bad thing, not just because your MPG goes out the window, but fumes can be dangerous inside the cabin area and volatile, however the pump is often very close to the left hand branch of an LCB and the pipe work is often even closer....

[crock]

A problem I have run into with SU pumps is that if you ever run out of petrol the pump will die a little after you have refilled the tank.

[dklawson]

A problem I have run into with SU pumps is that if you ever run out of petrol the pump will die a little after you have refilled the tank.

Electric or mechanical SU?

No worries Martin. I like the reassuring "tick-tick-tick" of an electric SU but they are not for everyone.
I have a sidebar comment on the fuel leak issue. Growing up I used to be much more aware of the condition of the car I was driving based on things like smells, sounds, and vibration. All these cues are gone with modern cars that are so quiet, odor free and smooth. Last week I pulled up to a stoplight and all of a sudden my gas gauge started falling like a stone. Instinctively I rolled down the window and started "sniffing" to determine if my car was really pumping fuel from a broken fuel line. Almost as soon as I started sniffing the needle bottomed out and began to climb again... apparently the victim of a car computer glitch or loose connection. Sometimes I miss the old days.

[MRA]

Oh the good old days...... where have they gone ?

[MRA]

A problem I have run into with SU pumps is that if you ever run out of petrol the pump will die a little after you have refilled the tank.

I last had an SU pump in about 1984, however I don't remember them doing that and used to run out of fuel all too often :-(