fuel pump questions

[J. Salmon]

I only have a few more questions

So my choices include an in-tank pump (as recommended by Kinsler - their part #10271) or possibly the slick external Purolator-Facet pump that Big-Foot has used (see Chuck and Ryan's build thread). I know that you can burn up a pump if you let it run dry with low fuel under braking. I also know it is not the best to suck on gas too much (though your results may vary) as with an external pump.

I like the Purolator pump because it can run for a long time dry. I like the in-tank pump because it will push instead of pull. But mechanical pumps pull...?

Can others share experience? Not having a lot of success searching, as not that many are running EFI, and many more still are doing in-tank baffles and the like, which I cannot do.

And if you do run an in-tank pump (brace yourself for the really dumb question) how the hell are you mounting the pump?

As usual, my thanks. -J.

 

[Ivan]

you could write a book on this subject :drunk:

from my reading of *cough* Fast Ford *cough* (uk performance ford magazine thingy) alot of high power track cosworths run dual systems, from my understanding this is a intank pump to a swirl pot, then annother pump to the engine. alot of people say this is the ultimate in fuel feeding. myself i honestly dont know, but as you have pointed out it is something to worry about.

(the above is my understanding, and may not be 100% correct :thumbsup: )

 

[J. Salmon]

I should have clarified that I am definitely running twin low(er) pressure pumps to a swirl tank (Kinsler's Vapor Separator Tank) and from there to the rails. I have the pump I will be using to feed the rails, but I am looking to choose pumps for the tanks, either inside or nearby.

 

[Ivan]

arrrr i see :thumbsup:

well i honestly dont know the answer to this problem :cry: but i do wish you the best of luck :thumbsup:

 

[Ian Anderson]

Something else to throw into the equation

If you are running vane pumps they generate heat that ends up in the fuel. So run a vane pump to the swirl and then another vane HP injection pump and you are adding a fair amount of heat. That and the fuel lines are in an engine bay that is also HOT.

The fuel in the tank acts as a heat shunt when you reurn the warm fuel to the tank but once you get down to a few litres it does warm up.

So I would recomend fitting a cooler in the return line back to tank that is in airflow under the car - a comon feature in small diesel engined vans etc,

How did I find this out?
I run tank to pollack valve to switch tanks, into a single filter, Facit Red top Swirl, Bosch return to swirl return to pollack return to tank

During shakedowns it all stoped so I checked if I had fuel and looked at the fuel filter and found it was soft to the touch due to heat!

Tank was probably 1/4 at the time and the day was hot. (30C plus)

So I now alternate tanks when in slow traffic which is when the heat builds up. (I will fit a cooler over this closed season)

Also my think on the low pressure pumps is that
1) The engine is fed from the swirl and so long as it has some fuel it will run
2) The engine will only draw full fuel as full throttle and how ofer will you bee at WOT for a long sustained period? (Damn corners get in the way)
3) So when the engine is not a WOT the Low pressure pump will catch up and refill the swirl pot.

My engine is running a limp 230hp and even at LE Mans Classic laps this year I did not get fuel starvation with a facit. Remember under acceleration the fuel is pushed rearwards in the long narrow tank.

In tank would be OK but how to mount and seal would be a problem that I wolould not like to tackle - I like the KISS principle and it is a lot easier to undo 2 connectors remove an in line pump and refit!

I don't have baffles and from 1/2 tank (on gauge not volume as the tank is bigger at the top) under braking the Facit note changes as it sucks air - at that stage the engine is on overrun / idle so is not drawing a lot of fuel from the swirlpot ( about 1.5l in my case)

I have also started my car after priming the swirl pot and only having fuel in 1 tank selected the empty tank and it ran for about 4 minutes on idle / blipping before duing through lack of fuel!

Enough for the moment but ask and I'll assist if I have tackled the problem!


Ian

 

[Paul Thompson 'Hooligan']

I normally use Carter 70gph lift pump(s) to feed the swirl pot and roller vane HP pump from the swirl pot to the rails.

I do try to avoid returning the fuel to the swirl pot though as I've noticed that circulating it around engine fuel rails back to tank tends to heat the swirl pot fuel quite a lot. I normally return to main tank(s), just make sure your lifter pump will keep up with the demand of the HP pump.

Also - make sure your pumps are rated adequately. The Bosch motorsport roller vane pump that is commonly used is reckoned to be good for approx 500BHP - but I know of people making 550+ HP that have required the use of 2 such pumps in parallel to keep up with demand. So do check that pressure under full load conditions too.

 

[mike]

btw.....
im running the TWM fuel injection with the accupump which calls for a dash 10 fuel line...fine and dandy, but the line coming out of the tanks is a dash 8.
are u guys changing those lines to a dash 10 to feed enough fuel??

 

[J. Salmon]

btw.....
im running the TWM fuel injection with the accupump which calls for a dash 10 fuel line...fine and dandy, but the line coming out of the tanks is a dash 8.
are u guys changing those lines to a dash 10 to feed enough fuel??

Is the pump in the tank and the line is downstream, or is the pump remote and the line is feeding it? If the line in question is on the pressure side of the pump, I would think you will be fine provided the motor is not mega hp. If the line is on the tank side and you are pulling though it, I would be more concerned. My understanding is that you want to minimize pulling a vacuum on the fuel to keep it from vaporizing. So, gravity feed with as big a line as possible.

 

[mike]

Is the pump in the tank and the line is downstream, or is the pump remote and the line is feeding it? If the line in question is on the pressure side of the pump, I would think you will be fine provided the motor is not mega hp. If the line is on the tank side and you are pulling though it, I would be more concerned. My understanding is that you want to minimize pulling a vacuum on the fuel to keep it from vaporizing. So, gravity feed with as big a line as possible.

well we changed our line coming from the tank.
it is a mega hp engine i suppose...
regardless, the point is that TWM calls for a dash 10 line feed, if the feed from your tank is dash 8, dash 8 is all your going to get and you wont be able to maximize the power you otherwise could get.
im just letting folks know that if your fuel injection system calls for a dash 10, be aware if you dont change the line from the tank u have a dash 8 feeding a dash 10. which means your not getting all the fuel the system potentially can handle and utilize.
i posted just as an FYI....

 

[Ian Anderson]

I have read
Allow 15cc of fuel per minute per HP

So a 300hp engine
300*15*60 = 270 000 cc per hour

This equals 270 litres per hour

Or about 60gph (The Facit Red top is rated near to this)

Thank goodness I am not constantly at max power as my full on car petol capacity would last 15 minutes!

Yes you want to be safe to avoid the engine running lean but at the same time you will not run for long!

Ian

 

[mike]

I have read
Allow 15cc of fuel per minute per HP

So a 300hp engine
300*15*60 = 270 000 cc per hour

This equals 270 litres per hour

Or about 60gph (The Facit Red top is rated near to this)

Thank goodness I am not constantly at max power as my full on car petol capacity would last 15 minutes!

Yes you want to be safe to avoid the engine running lean but at the same time you will not run for long!

Ian

well when ur tuning the engine via fuel injection, you will tune it to how much fuel you have available, be it fed from a dash 8 line or 10.
a dash 8 line wont allow as much fuel as a dash 10 and you would tune accordingly.
nothing to do with "safety" but more to do with utilizing full potential.

 

[J. Salmon]

OK, I get the concept that you need adequate fuel. But I thought that the EFI was tuned via constant pressure to the injectors. So the pump simply has to maintain the pressure you set via the regulator. if you have a -8 feed line, the pump will have to work harder (more resistance) to get the pressure at the injectors vs. a -10 line. But I thought you tune via pressure at the injectors, not flow rate. You just need to make sure you have enough flow to sustain the pressure you are wanting. Certainly, if you do not have adequate pressure, you will not get as much flow and could be leaving hp on the table.

Am I screwed up here?

 

[Ian Anderson]

Efi is based on a set pressure at the injectors - this is done by the regulator at the end of the fuel rail that thn allows the excess fuel pumped to be returned to the tank / swirlpot.

The bigger pipe will flow more volume than a smaller pipe at the same pressure so as your fuel requirement increases you may need to increase the pipe diameter.

The low pressure side would normally be a bigger diameter pipe as it is at lower pressure

As my motor is small at 3.9litres and about 230 hp I can cope with 8mm pipe on both feed to and flow from the HP pump - so it also made it esier to get all the fittings the same size

Ian

 

[mike]

OK, I get the concept that you need adequate fuel. But I thought that the EFI was tuned via constant pressure to the injectors. So the pump simply has to maintain the pressure you set via the regulator. if you have a -8 feed line, the pump will have to work harder (more resistance) to get the pressure at the injectors vs. a -10 line. But I thought you tune via pressure at the injectors, not flow rate. You just need to make sure you have enough flow to sustain the pressure you are wanting. Certainly, if you do not have adequate pressure, you will not get as much flow and could be leaving hp on the table.

Am I screwed up here?

the part i bolded touches on the point im making.
in ian's post above, it doesnt matter if hes running a dash 8 or a dash 10. his engine isnt going to need that much fuel.
in another application where your building a hp motor, it may make a difference.
keep in mind im not saying it wouldnt be a "safe" tune either way.
your statement is correct in what im saying in that one MIGHT be leaving some power on the table because you can only feed as much fuel as your smallest line can feed. in the spf, that would be a dash 8 unless you change it. i changed mine because the TWM fuel lines are all dash 10.
none of this may even apply to you, i just threw it out there as an FYI.

 

[Paul Thompson 'Hooligan']

Below 400HP, -6 all throughout would work fine..

I try to at least have a gravity feed -8 min from the swirl pot to the HP pump.

If your HP fuel line splits and travels down both sides feeding 4 injectors each side, it will feed more easily than a 'long line of 8' injectors. Although pressure fluctuations will normally only be detected on the long line method at wide open throttle, where demand is greater. The dual feeds effectively being the same as larger volume fuel rails.

It is normal on normally aspirated engines to map to a specific fuel pressure, that best suits the injector's spray pattern - eg 45-55psi.

BUT

IF you have a higher power engine, say 550+ HP, it sometimes becomes difficult to get regulation friendly emissions when larger injectors have a hard time opening/closing fast enough to control the small amounts of fuel required for idle/part throttle.

In this instance, connecting a vacuum pipe to the fuel pressure regulator to vary the fuel pressure can help, as at idle, the fuel pressure is pulled down to say 35psi, which in turn means larger (more accurately controlled) injector opening times.

This is also done on Forced Induction engines, where running say 10psi of boost would mean that the injectors would be fighting a losing battle. Imagine the extreme, with a fuel rail pressure of 45 psi, at 45 psi boost, nothing would flow out! So fitting a feed from the manifold to the pressure regulator in this instance will widen the range of control for the injector further. Off boost with vacuum, the fuel rail pressure drops to say 35psi and on boost, it becomes the norm 45 + the boost pressure to overcome the increased manifold pressure.