31 replies to this topic

[rally1380]

Hi

I'm currently in the throws of fitting twin HS4's to my 1380 engined rally car so gonna ditch the mechanical fuel pump which currently pumps the expensive stuff into the carb.

1380cc, Big valve ported head, unknown cam (until i need to pull engine apart) and obviously twin HS4's.....if spec matters to question below?


My query is this.....as far as i'm aware, SU's like around 3 psi of fuel pressure so why is it that minispares seem to recommend the competition spec ones for the twin hs4 job pumping way in excess of 3psi.

Demon tweeks state that the Facet solid state Road spec pump will deliver 3 psi and recomend this pump for up to 120 BHp so who's right?

Which pump and spec is best for my purposes?

Oh, and i plan to use a fuel regulator too (if that matters)

Cheers.

[R1minimagic]

Its the flow rate of the pump thats more important than the pressure, you only need 3-4psi

[rally1380]

So when you say flow rate what do you mean?

I was advised that Facet's bog standard road spec (the square pump) would be ample....and the specs agree but wanted to check before i shelled out.

Also don't understand why minispares write up's on these says different.

[R1minimagic]

Check on here for specs vs your application

http://www.merlinmot..._159/index.html

[Cooperman]

I use a Facit road pump on my rally 'S'. In fact to make it 'fail-safe' I actually run two of them mounted under the rear seat base panel, within the rear sub-frame, and piped in parallel with completely separate wiring, switching and fusing for each. One is connected to the ignition 'on' circuit and the other has a separate switch on the navigator's panel.
A pressure regulator is mounted just before the carbs (twin H4's) and the pumps have a 3 mm thick aluminium shield covering them. As the exhaust is centre-exit access to the pumps is easy.

I hope this helps.

[dklawson]

To add to what has been said above, you want about 3 PSI at the carbs. You can achieve this with a properly selected 3 PSI (max) pump OR you can buy a higher pressure pump and use a pressure regulator right before the carbs to drop the pressure. Higher pressure pumps generally can move more fuel (gallons per minute) but that is not always true. Most makers will list their pump flow and pressure to help you make your selection.

When people focus on the pump in terms of the engine power (for example the listing you mentioned where Demon Tweeks said such-and-such pump is good to 120 BHP) you have to consider this statement in terms of how you are using the car/engine. Cooperman mentioned the pump arrangement on his rally car. He is going to be putting more demands on his car's fueling during competition than a normal road going car will.

If you are going to use this car primarily on the street, no matter how powerful the engine is, you are not going to put excess demands on a "stock" pump. Short bursts of speed and acceleration will draw more fuel but those are short periods, not continuous. It is highly unlikely that on the street you are going to be calling on your engine's full power reserve for more than a moment at a time. If on the other hand you are going to compete with this car as Cooperman does with his rally car, that's when you may want to consider a pump with higher flow and pressure and using a pressure regulator right before the carbs to achieve the desired 3 PSI. It really comes down to how you are planning on using your car.

For most street installations the relatively inexpensive square bodied Facet pump is more than enough. There are a couple of square bodied Facets that produce right at 3 PSI so no regulator is required. The so-called red/gold/silver top Facet pumps are a bit nicer and quieter though most are rated for higher than 3 PSI (meaning you also should buy a regulator) and cost a bit more. Consider how you plan on using your car and what your budget is when deciding what to buy.

[rally1380]

To add to what has been said above, you want about 3 PSI at the carbs. You can achieve this with a properly selected 3 PSI (max) pump OR you can buy a higher pressure pump and use a pressure regulator right before the carbs to drop the pressure. Higher pressure pumps generally can move more fuel (gallons per minute) but that is not always true. Most makers will list their pump flow and pressure to help you make your selection.

When people focus on the pump in terms of the engine power (for example the listing you mentioned where Demon Tweeks said such-and-such pump is good to 120 BHP) you have to consider this statement in terms of how you are using the car/engine. Cooperman mentioned the pump arrangement on his rally car. He is going to be putting more demands on his car's fueling during competition than a normal road going car will.

If you are going to use this car primarily on the street, no matter how powerful the engine is, you are not going to put excess demands on a "stock" pump. Short bursts of speed and acceleration will draw more fuel but those are short periods, not continuous. It is highly unlikely that on the street you are going to be calling on your engine's full power reserve for more than a moment at a time. If on the other hand you are going to compete with this car as Cooperman does with his rally car, that's when you may want to consider a pump with higher flow and pressure and using a pressure regulator right before the carbs to achieve the desired 3 PSI. It really comes down to how you are planning on using your car.

For most street installations the relatively inexpensive square bodied Facet pump is more than enough. There are a couple of square bodied Facets that produce right at 3 PSI so no regulator is required. The so-called red/gold/silver top Facet pumps are a bit nicer and quieter though most are rated for higher than 3 PSI (meaning you also should buy a regulator) and cost a bit more. Consider how you plan on using your car and what your budget is when deciding what to buy.

Cheers Doug L.

kinda what i was thinking all along but wanted to hear it from someone else as a confirmation.

The car isn't really used for road use...(i'm lucky enough to walk to work)....it is purely a competition and weekend tool. Got a rally booked for early march, hense wanting to get things sorted sooner rather than later so i can have a few weeks for tweeking...or as is normally the case...last minute panic with stuff not going to plan!!!!

[Cooperman]

The 'S' goes down to about 12 mpg on competitive sections and even then one of my twin Facit 'square' road pumps is quite sufficient.
Quoting a pump against bhp figures is misleading as it's the application of the power, not the power figure, which is important.
I do sometimes run with both pumps 'on', but that is just to 'exercise' the 2nd pump which would otherwise not get used at all.

[rally1380]

The BHP figure i gave was an 'up to ' figure...they also quote engine sizes. I was more interested in the fuel pressure delivery...the 3 psi figure.

I was more wandering why minispares seem to insist on much more powerful pumps when obviously the road spec one can quite happily fuel the monster 'S'. maybe they just want to shift more expensive pumps and regulator's.

[R1minimagic]

It's best to match the pump to the power requirements and then have a little bit of extra flow rate capability in reserve. If you buy a pump which has much higher flow rate and pressure than required and then use a pressure regulator to reduce psi to the carbs, then you are just increasing pumping losses and more likely to develop other issues, such as fuel leaks and battery/charging issues!

[rally1380]

It's best to match the pump to the power requirements and then have a little bit of extra flow rate capability in reserve. If you buy a pump which has much higher flow rate and pressure than required and then use a pressure regulator to reduce psi to the carbs, then you are just increasing pumping losses and more likely to develop other issues, such as fuel leaks and battery/charging issues!

So in other words.....i should go with cooperman's advice and purchase a 'road' spec facet pump as that gives the correct 3 psi required by su's.


Specs....

Road - 12 gallon/hour, pressure of 2.5 - 3 psi, up to 130bhp

Fast road - 18 gallon/hour, pressure of 4.0 - 5.5 psi, up to 150bhp

Competition- 25 gallon/hour, pressure 0f 6 - 7 psi, up to 180bhp.

[Cooperman]

No, you should buy 2 off Facit Road Pumps and pipe them in parallel. Then wire them independantly and you'll never retire from a rally with a failed fuel pump. You might well retire with broken transmission, but not failure of the fuel supply .
I just have mine bolted solidly to the rear seat base panel. The fuel tank outlet goes to a 3-way fitting with the other two feeds going one each to the pumps. From the pump outlets the pipes go to another 3-way comnnector with the outlet going through the inside of the car to the front bulkhead, through the bulkhead near the wiper motor to the fuel pressure valve and from there to the twin H4's. The pipe inside the car is one continuous length of metal pipe with no joins at all (as required by the MSA regulations).
Each pump has its own separate earth connection and is switched separately, one from the ignition and one from a switch. They have separate fuses.
It's 'Fail-Safe'.

[R1minimagic]

Depends how paranoid you are about the fuel pump failing, highly unlikely IMO but if you were going to the moon you would fit 3 and carry spares just in case!!

[Cooperman]

Most rally cars, especially historics, run two separate pumps. Having retired from an event back when Minis were new because the SU petrol pump failed I have always fitted two pumps. A popular solution was the old Jaguar 'twin-knocker' pump which was like two pumps.
When you've paid, say, £250 to enter a rally, plus hotel costs, fuel for the event an 'on-event' insurance it's a shame to have to retire with a failed petrol pump.

[Cooperman]

The 'works' used to fit the Jag twin pump inside the car under the rear seat overhang, but that was deemed unsafe (I wonder why) by the FIA and they moved them into the boot where the pump sat with up to 11 gallons of petrol and a battery! That is supposed to be safe.
I've always fitted mine under the rear seat base with a shield, which is easy if there is a centre-exit exhaust.