Tuesday, December 26, 2006

Fuel Pump sizing

My fuel pump pressure post gave me a lot to think about, and few people had some interesting questions as well. One of the simplest, yet most important questions was 'is the fuel pump holding up?' I looked around, and amazingly, I have not found much information on how to estimate how much fuel your fuel pump needs to be able to pump so injectors can keep with the demand.

Most fuel pumps are rated in how many Liters of fluid they can pump an hour. I'm not exactly sure why they'd go with a volume flow rating, when injectors are mass flow rated. The easy way around it is to convert one to the other, which should be easy, as mass=density*volume. Of course there are various types of gas, so the density specific to particular types of petrol will differ, but the generally we should be close to desired rating. I found numbers of 690g/L to 770g/L, so I'm going to use 730 for an easy average. These translate to 0.690kg/m^3, 0.770kg/m^3 and 0.730kg/m^3 respectively, for the more traditional measure of densities.

This spreadsheet converts the rated flow of the pump into units comparable with the units used for injectors, and then divides the flow of the pump by the number of injectors, to see if the flow provided to each injector is larger than what the injector would flow at WOT at standard LSx 58psi fuel pressure.

It's all very simple, but the funny part is that once I started plugging in typical fuel pump flows, the per injector flows were very closely matched to the flows provided by the popular injector sizes!

190 lb/hr fuel pump outputs just above what SVO red tops need.
255 lb/hr fuel pump outputs just above what SVO green tops need.
350lb/hr fuel pump outputs just above what Mototron 60's need.

I'm not sure if it's coincidence or not, but it works so nicely, it's a really easy 'rule of thumb' to match injectors with pumps for a well balanced system.

Here's the DOWNLOAD if you want to play with more specific options.

More fuel system investigations coming soon.
Stay tuned,


At 9:03 PM, December 31, 2006, Anonymous Anonymous said...

Marcin - Good luck on your Masters Thesis. Hopefully by the time you finish I'll be caught up on your other published works and ready for more.



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