Re: 2005 Honda Civic LX gas mileage



Elle wrote:
>> I did say "virtually constant" and you missed a significant factor
>> (for in-tank pumps in the Honda/Rover cars) which is that the fuel is
>> sucked into the pump without being replaced by air from the outside
>> thus reducing the absolute air pressure in the tank. You can verify
>> this by listening for the 'whoosh' of air into the tank when you
>> undo the tank's filler cap.
>
> One should note here that, as long as the tank is not vented to
> atmosphere, then the pressure due to the air above the fuel level in
> fact will be reducing (contrary to the implication above)

It isn't contrary - that is exactly what I said - "reducing the absolute
pressure in the tank"!

> as long as
> the fuel level goes down. Thus the pressure at the pump inlet will
> be even lower than if the tank were vented to atmosphere.

Agreed.

> With no venting, even more pump work is necessary than with venting.

Agreed again.

> It's mere theory, and in this application out in left field, because
> the pump is such a low power device, raising say 1 gallon / hour a
> few psi, well less than 1 hp of motor power, I'd guesstimate with
> some rough calculations.

Your figures are a bit adrift though. Yes I know they are guesses but
since the pump needs to raise the delivery pressure at the filter so
that the engine's FI is supplied with enough fuel at the most extreme
of power demands and RPM, the volume at a guess is far higher than
1 gallon / hour. That fuel which isn't consumed by the FI injectors is
returned to the tank through a pressure relief valve. So at 90 mph
the engine will be burning around 3 gal / hr or more and that figure
doesn't include the amount returned to the tank.

Here are some figures to play with. The pump output pressure runs
at 2.3 to 3.0 bar (that's about 33 to 44 psi). At 16volts it can deliver
at nearly 60 psi. Figures taken from Haynes for my Honda engined
Rover 216 16 valve 1.6 litre.

How do those numbers run out at HP needed from the pump?


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