Lotus Elan

Fuel pumping rate

PostPost by: street » Sun Oct 06, 2024 3:34 am

My pump flow rates over 3 litres are as follows:

Test 1
500 ml - 1min 15 secs (75secs)
1000 ml - 2min 30 secs (75secs)
Test 2
500 ml - 1min 10 secs (70secs)
1000 ml - 2min 25 secs (75secs)
test 3
500 ml - 1min 10 secs (70secs)
1000 ml - 2min 23 secs (73secs)


So I have constant fuel pump pressure, however is this sufficient for standard Twinkie.

Thanks
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PostPost by: Andy8421 » Sun Oct 06, 2024 6:32 am

Flow isn't pressure.

Assuming you have Webers, internet consensus is that fuel pressure should be 3.5psi. This is important as Webers are prone to flooding with too high a fuel pressure.

Flow requirements are a different matter, this is set by the HP your engine is producing. Lets assume your engine can produce 100BHP at wide open throttle. There are lots of assumptions that go into how many litres per minute you need per 100BHP, but a quick average of numbers I could find on the internet seemed to indicate about 0.4 litres per minute (the range was really wide, so this number could be way off - please treat with caution).

So on the basis of the above numbers, to avoid flooding and provide enough fuel to avoid starvation at full throttle, you need a pump that has a 3.5psi output, that can flow at least 0.4 litres per minute at this pressure. The flow rate drops off as pressure increases - reputable pump suppliers provide a flow vs pressure graph, or alternatively quote a HP range that the pump is suitable for (so they have done the flow to BHP calculation for you).
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