Fuel Injection, What pump to use? 4

[Spimage]

I have a 377 cu in chevy motor in my cobra (Prototype) and am having a problem with the fuel injection system,in that, I'm told that the system needs a constant 3 bar (50lbs) pressure up to max revs. However, on the dyno, at 4500 rpm the pressure starts to drop off. I need to decipher what fuel pump to install in order to overcome this problem. At the moment I am getting a flow of 1 litre / 20 seconds from the return line. Is there a formula to calculate what the return flow rate should be? On paper, this motor should push out in the region of 600 hp. Any assistance in this regard would be greatly appreciated.

Warren

 

[1Bluegrass]

We need to know what kind of pump system you now have.
In general, the fuel system will be rated in L/HR as you have stated.
My knowlwge of FI is that you need a hi pressure pump sized to deliver enough fuel at the injector working pressure and ECM derived max. pulse width in the (90% range) to supply enough fuel to support 600 hp.
This supposes that the engine is set up properly without adding it's own tuning problems to the basic question.
The pump size that will handle your power is one in the 250 L/hr delivery rate range at 40 to 50 psi drop accross the injectors and should be a two pipe system with a regulator.
Rememmber that there are various pumping volume capacities at the same pressure. This means that as you raise the operating pressure of any given pump system, the volume goes down, so it is important to size the pump to the volume needs at the operating pressure. Don't use lines that are too small to haandle the delivery volume regardless of pump size.

 

[optimum]

http://www.msdignition.com/fuel_6.htm

http://www.weldonracing.com/d2015.html

http://www.weldonracing.com/d2025a.html

 

[Spimage]

1Bluegrass

Thank you for the prompt response to my query.
I am using two Bosch pumps in parallel connected with a Y piece into a 10mm line to the motor. The Y piece at the motor end, feeding the rails is 6mm, being the same size,
as the bridge between the fuel rails as supplied by crowd from whom I bought the system. The return line to the tank is 8mm. Thanking you, or anyone else on this forum, in anticipation of further input.

Warren

 

[WGJ]

Hello Spimage, I take it that your engine is naturally aspirated / not super or turbocharged, based on your use of a 3 bar supply?
Is 600bhp a reliable estimate of power, that works out to 100bhp/litre or 1.59bhp/cu in? Quite a high specific output.

If 600bhp is real then you need about 270 lph @ 3 bar to satisfy the engine, plus some extras to satisfy the vehicles overall fuel handling requirements.
For example, the regulator needs to pass a certain amount of fuel to keep it in it's linear operating area. Then you need to make some allowance for pump wear-out. Then you need to allow some excess flow to cope with high ambient temperature conditions where you may generate vapours that need to be purged from the supply system.

May I suggest that, to get 600bhp installed in the vehicle, you need:
Engine 270lph min
Regulator* 15 - 40 lph
Wear out 10% of total so far
Hot fuel handling 10% again as a minimum.
(*: based on Bosch regs. Minireg 15lph, standard reg 40lph)

This totals about 375 litre/hour for a reliable system.
Next problem: as you're running a full return system, at idle almost all of this will be going back to the tank. All this flow down an 8mm return line will change the characteritics of the regulator due to back pressure so you may want to consider a bigger line. All this flow will also cause a lot of vapour generation in the tank which may be undesirable and will likely age the fuel quickly by driving off the 'light ends'.

I am sure that there is a Bosch chassis-mount pump that will do 250lph at 3 bar and there are Pierburg pumps in their E3TS range that will also perform like that. I'll try to find the Bosch number.

One further thought - have you sized the fuel pump wiring correctly?
Check the battery terminal voltage and then check the voltage at the pump terminals.
If there's any more than 0.75 volt difference you are losing flow straight away.
Electric FI pumps are quite voltage sensitive and the high flow Bosch pumps can take up to 12 amps on load. At this current flow, a 0.1 ohm resistance in the supply wires will drop the pump voltage by up to 1.4 volts, depending on battery condition.
You need to use the heaviest wiring you can manage to keep the resistance down and the pump terminal voltage up.
If the pump is fused, don't share the fuse circuit with any other electrical loads and make sure the fuse is top quality, low resistance.

Hope that helps.

 

[WGJ]

I'm afraid I couldn't get a Bosch part number for the pump I mentioned.

However, the Ford data for the pump is as follows:
Part Number: 86AB 9350 CA
Finis Code: 6163388

This is a European application, if you're in the USA a friendly Ford dealer might be able to order you one using the 'Finis Code' noted above.
A Bosch agent might be able to find the pump from the application, which was the European turbocharged Escort, 1600cc, Bosch KE fuel system, 1989 model year.



The pump was specified at 5.8 bar and flowed 180 lph with a 12v supply. Current like this is over 12 amps.
At 3 bar, I used to see over 250 lph with current in the order of 10 amps.

 

[magnograil]

Spimage - Your feed rail sounds small. My 2.5L V6 Alfa Bosch injection has about a 10mm ID rail each side. It also matters whether you are using batch injection or sequential. Batch requires the rail to feed all the injectors at the same time. If so you might need an accumulator to handle the intermittant pressure drop.

 

[schmidtj86]

You may also be experiencing some manifold vacuum at those revs, and with a vacuum referenced pressure regulater, it will reduce the pressure proportionally. But, the math supplied above is close (but my calcs put the engine at needing around 175 L/hr before factors of safety). At your current 180 L/hr (1 L/20 sec), I'm pretty sure it's not enough, if you factor in a factor of safety. BUT, this engine isn't making 600 hp at 4500 RPM, it's probably 600hp at 7000+ RPM. This may be an indication again that the pressure drop is caused by the regulator referencing, and is not actually a problem, at 4500 RPM. As you should know, regulator referencing is a good thing (unless your efi computer knows that it is unreferenced) as it keeps the pressure difference across the injector CONSTANT, no matter what the manifold pressure is, thus keeping the injectors at the same flow rate all the time.
Magnograil is also right, in that batch or bank systems will have a pressure drop when all injectors fire in one rail, and this can cause problems at certain RPMs, and be fine at others. Dead-headed fuel rails really cause this problem to appear.

 

[EdDanzer]

You may need a check valve at the end of each pump. If one pump pumps more it will over power the other and reduce total flow.

 

[schmidtj86]

EdDanzer,
If the system pressure is set to 50 psi, and both pumps each are capable of deadheading to probably 200 psi (or anything greater than 50 psi + some pressure drop), then both pumps will contribute to flow. One way 2 pumps (or even one big pump) could be a problem is if the suction side feed lines are too small. The suction side can start to cavitate (basically cause vaporization in the line). That'll chew up the pumps, and reduce their capabilities.