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Author: Subject: Required Fuel Flow for BHP
davidimurray

posted on 28/5/14 at 10:45 AM Reply With Quote
Required Fuel Flow for BHP

Just wondering if anyone had seen any figures for the required fuel flow to produce a certainn BHP?

Just curious as while testing my blocked fuel filter I measured my ZX6R pump as giving out 1L / minute and wondered what that would be good for.

I have seen one suggestion on the internet, which was to multiply BHP x 0.38 to give L/hr - which if correct gives 157 BHP from the pump.





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DW100

posted on 28/5/14 at 11:41 AM Reply With Quote
I'd hope you didn't need 1 litre per minute for 157 Bhp as you soon empty your tank

Are you getting ltrs/hour and ltrs/minute mixed up?

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Mr Whippy

posted on 28/5/14 at 12:07 PM Reply With Quote
A 60L tank gone in one hour, big engine...depressing
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umgrybab

posted on 28/5/14 at 12:13 PM Reply With Quote
You can calculate your theoretical power by calculating the energy in 1 Litre/60 seconds mixed with oxygen at the correct a/f ratio then multiplied by the efficiency of the engine (approximately 0.33). This will give you a power unit (Joule/second or Watts) that you will then have to convert to BHP.

Using the energy in petrol as 42.4 MJ/kg and the density as 0.74 kg/L we get 31.376 MJ/L
multiply this by 1 L/60 s gives us 522.933 KJ/s or 522933 J/s or 522933 W
multiply by 1 BHP/ 0.7457 W gives 701.265 BHP then multiply by efficiency of 0.33 gives a theoretical maximum power of 233.76 BHP, with the units i quickly googled.

But don't forget that your measurement may not have included the resistance of fuel line, filter, injector jets. This could be much lower once all of that is accounted for.

[Edited on 28/5/14 by umgrybab]

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Slimy38

posted on 28/5/14 at 12:23 PM Reply With Quote
quote:
Originally posted by DW100
I'd hope you didn't need 1 litre per minute for 157 Bhp as you soon empty your tank

Are you getting ltrs/hour and ltrs/minute mixed up?


It actually sounds about right to me, if you run your car at 157 bhp for an extended period of time you could quite easily burn through a litre a minute. You'd have to be on an oval track at full speed though, that's the only time you'd actually be using such a high power for a long period of time. Out in the real world you don't use anywhere near 157 bhp.

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davidimurray

posted on 28/5/14 at 01:20 PM Reply With Quote
quote:
Originally posted by umgrybab
You can calculate your theoretical power by calculating the energy in 1 Litre/60 seconds mixed with oxygen at the correct a/f ratio then multiplied by the efficiency of the engine (approximately 0.33). This will give you a power unit (Joule/second or Watts) that you will then have to convert to BHP.

Using the energy in petrol as 42.4 MJ/kg and the density as 0.74 kg/L we get 31.376 MJ/L
multiply this by 1 L/60 s gives us 522.933 KJ/s or 522933 J/s or 522933 W
multiply by 1 BHP/ 0.7457 W gives 701.265 BHP then multiply by efficiency of 0.33 gives a theoretical maximum power of 233.76 BHP, with the units i quickly googled.

But don't forget that your measurement may not have included the resistance of fuel line, filter, injector jets. This could be much lower once all of that is accounted for.

[Edited on 28/5/14 by umgrybab]


Interesting, I like the thinking, but the figure seems much higher than I expected. I found another set of working out here - excuese the american units - http://www.chevytalk.org/fusionbb/showtopic.php?tid/240020/





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matt_gsxr

posted on 28/5/14 at 02:01 PM Reply With Quote
If you want to sanity check some numbers then you can see what power output cars have with which fuel injectors.
Injector duty cycle maximum of maybe 80%.

For example gsxr1000 k2. 155bhp. 4x240cc/min injectors. So your pump will easily support 157bhp.

Generally fuel pump outputs are way over specified simply because it is the safe thing to do. Otherwise on the day when the voltage is a bit low, the fuel filter a bit clogged, the air a bit cold, and the driver a bit keen then the fuel pressure drops and it all goes molten pistons.


Have you noticed that if you reverse the polarity on those mitsubishi pumps that they still work, but pump less fuel? Well mine did.





http://jpsc.org.uk/forum/

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hughpinder

posted on 28/5/14 at 03:40 PM Reply With Quote
1lt/min would give about 190bhp, with no fuel return. (the formula is 0.19*cc/min=bhp. For the injector example, you get 157 bhp from 960cc/min (4*240cc/min) of injector because you wouldn't run them at 100% duty. I suspect this is about right, or you could start to suffer from misfueling, so you always have a bit of spare duty on the pump.
Regards
Hugh

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big-vee-twin

posted on 28/5/14 at 05:47 PM Reply With Quote
link





Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016

http://www.triangleltd.com

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coyoteboy

posted on 31/5/14 at 08:19 AM Reply With Quote
1 litre a minute is a fairly small engine, my 2 litre turbo runs 550cc injectors at 90% at Max load, 2 litres of fuel going a minute no problem.

Also, are you checking the pump loaded at full pressure or just open flow?






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davidimurray

posted on 31/5/14 at 11:29 AM Reply With Quote
quote:
Originally posted by coyoteboy
1 litre a minute is a fairly small engine, my 2 litre turbo runs 550cc injectors at 90% at Max load, 2 litres of fuel going a minute no problem.

Also, are you checking the pump loaded at full pressure or just open flow?


Only tested open ended, but with all the fuel filters in place as I was checking for restrictions. The pump is used on the zx6r and zx9r so should be good for around 140bhp.

What sort of power are you getting from your 2 l turbo at those flows?





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coyoteboy

posted on 31/5/14 at 11:47 AM Reply With Quote
Open flow rate will be much higher than at 3 bar, depending on the pump type exactly.

Typical flow chart;



I'm playing around the 300 mark, with some overhead (running lots of fuel top end to keep it cool, could lean out a lot but ~330 is about the known limits for the 550 injectors on this engine).






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davidimurray

posted on 31/5/14 at 02:59 PM Reply With Quote
As my setup is carbs and the zx6r pump is for carbs the pressure is only just a couple of psi.

Was curious as to the fuel pump capacity as I plan to transfer my setup from my 1800 pinto over to a Duratec when I swap engines.





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coyoteboy

posted on 31/5/14 at 03:25 PM Reply With Quote
My bad, assumed EFI! Should be fine then!






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