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The mkiv Supra Owners Club

Quad Fuel Pump Setup


Noz
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Using OEM pumps (1 or more) which the big Walbro pumps are, would be more reliable than a big single aftermarket external single fuel pump.

 

As for the danger of a pump failing, for a built engine you should always have a fuel pressure sensor hooked up to the ECU, so you can shut the engine down quickly. A single pump failing at max boost could still take out the engine.

 

You should stage multiple pumps, so you would be running just one pump when off boost (99% of the time), which would be way quieter than a big external pump.

 

I run two Walbro pumps, staged so one comes on at 10 psi boost so is very quiet off boost and when on boost the exhaust drowns out any extra fuel pump noise. I also run a fuel pressure sensor as well. :)

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a complete fuel pressure drop out is going to safer for the engine, it'll lean to a point where there is no chance of ignition, even with ecu fail safes you'll always get a few engine cycles before the ecu shuts things down.

 

with multiple pumps you'll get enough flow from the working pumps to supply the engine but when needed the extra one won't come in and lean out dangerously.

 

the only down side is if the single pump fails your going to be stuck, but with multiple units you can atleast baby the car home. But in my experience a single system is so much safer, plus the benefits of using a swirl pot to prevent any surge issues.

 

Tim

TB Developments

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i know, i've never seen the point of these multiple pump setups. the large external is more reliable

 

They are noisier (without a controller) and what I've read, the failure rate of the big external pump is a lot higher for some reason.

 

Most modern aftemarket ECU's have AFR lean limits so the ECU would cut fuel if you would start to run lean at wide open throttle in case of a fuel pump failure.

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a complete fuel pressure drop out is going to safer for the engine, it'll lean to a point where there is no chance of ignition, even with ecu fail safes you'll always get a few engine cycles before the ecu shuts things down.

 

You probably also get a few engine cycles where there is still enough fuel to detonate when a single pump fails. I don't know if anyone has ever done a test to see which is best, but my guess is that the ECU will shut the engine off quicker.

 

with multiple pumps you'll get enough flow from the working pumps to supply the engine but when needed the extra one won't come in and lean out dangerously.

 

That's why you always need a fuel pressure sensor hooked up to the ECU if using multiple pumps.

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In theory the reaction time should be the same regardless of pump size.

 

So if the ecu does it's job in theory there's no difference on safety as long as you have pressure and afr covered. The mechanical means of sending fuel shouldn't affect the reaction time of the electronics.

 

So if you can reduce noise on a staged system and maintain reliability why are bigger pumps more popular?

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Down here in NZ, with the high hp street Supra's that I know of, the multiple pump option seems to be more popular. More complex to setup and tune are the downsides.

 

If building a racecar that will see little to no street time, then a surge tank, feeder pump and big single pump is what most people use as pump noise does not matter and it is simpler to setup and tune and you get a larger surge tank vs the small in-tank surge container that the Supra has.

 

Thinking more about how long you would get detonation for when a single pump failed, I think it could be quite a long time. Comparing to a water hose being turned off, it probably takes 1 second for flow to drop to near zero when the tap is turned off. If the same is true for injectors, then the a/f ratio could be in the detonation range for up to 1/2 second. At 8000 rpm with a 6 cylinder, this means there could be hundreds of detonations that occur before the a/f ratio is too lean to detonate. Does anyone know of any research in this area?

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