[Diy_efi] Fuel Pump speed controller

[efi_student]

Maybe not so dumb.  Toyota is using a returnless system on their Group A
rally car.  From someone very close to the source:

"The reasoning is, its easer to keep the fuel pressure controlled
without all the changes in engine temp in the mix. Also the controlled
fuel evaporative keeps the fuel not only cool but in a controlled
condition, this also helps with tuning and better mapping across the
board, as the fuel is not all over the scale in temperature. Another
benefit is weight, far less plumbing in the car no return line, no
evaporative lines and fittings, evap tank separator its all gone one
neat compact unit in the tank looks after all including fuel pressure."

Initially I would have agreed with your analysis, but there is certainly
something to be said for stable fuel density.  Having come from vacuum
systems and gas control devices, I have always thought the method of
controlling fuel pressure pre-regulator a bit at odds with industry best
practice for gas systems.

Lance

-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On
Behalf Of Greg Hermann
Sent: Saturday, August 03, 2002 11:14 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] Fuel Pump speed controller


At 12:40 AM 8/4/02, Scott F. Williams wrote:
>Please educate me as to why you'd want to control the speed/output of 
>the fuel pump. Isn't the fuel pressure regulator the proper way to 
>control the pressure to the fuel rail, etc? I'm obviously missing 
>something here...
>--
>Scott F. Williams

If he's talking about a non-return fuel system, would be one reason, but
that is really a dumb design for performance use.

A better reason is that two controls over a variable will give a MUCH
tighter, more accurate control over the controlled variable--in this
case fuel rail pressure.

Kind of like the way heavy trucks use a thermostat AND (sometimes)
radiator shutters AND (occasionally) a variable pitch cooling fan to
control coolant temp.

Greg




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