Tuesday, April 26, 2022

A useful bit of fuel math.

Chatting with a friend, he mentioned that he didn't think the low pressure pump that GBS provided with his kit would sufficient. That got me thinking about my own car and whether or not my fuel pump would be sufficient for supplying my 2.5L engine.

Time for Maths.

How Much Fuel Does My Engine Need

The injectors plugged into my ATR throttle bodies are Bosch 0280 155968 which are rated to 453cc/min @ 3 bar. The table below shows up the fuel flow required at 80%, 85%, and 90% injector duty cycle.  (Technically I should be doing this by fuel mass/weight to be super precise but volume is fine for my use.)

Injector cc/minGPH @ 3BAR80%85%90%
Total Flow (x4)28.723.024.425.8

So this tells me that I need to be able to supply the engine between 23 and 26 gallons per hour from the tank. Cool.

How Much Fuel Can I Push From the Swirlpot to the Injectors

The high pressure pump between the swirlpot and the injectors is a Bosch 0-580-464-015. This pump moves 34gal/hr @ 3bar. That ~32% more than would be required running at 90% duty cycle. (And running at 90% is dumb, realistically I'm going to top the injectors out around 80%)

Sweet! No changes needed there.

How Much Fuel Can I Push From the Tank to the Swirlpot

The low pressure pump is a Facet 40105 that can move upward 30gal/hr @ 5psi.  This pump will provide 16% more fuel than required at 90% duty cycle.  Should be plenty.

How Long Can I Run the Car at full load?

You wouldn't really run the car at full load until the tank is empty but it's a reasonable metric to know if you're into motorsports.  Say a track day with 20 minute sessions where you do spend not an insignificant amounts of time at wide open throttle. Knowing that it's possible to blow through the majority of your fuel tank in a single session gives you an idea of how frequently you're going to have fill the car up throughout the day. (Basically, you need to top-up after every session.)

On The BoilMinutes Till Empty


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