[Diy_efi] Intro, and q's about fuel economy

Greg Hermann bearbvd at mindspring.com
Mon Dec 16 00:52:31 GMT 2002


At 4:02 PM 12/15/02, James wrote:
>On Sun, 15 Dec 2002, William Shurvinton wrote:
>
>> As for the actual EFI. If you are not after meeting any emissions regs
>> you can build very simple EFI. Have a search on how some of the old
>> Bosch stuff worked. K-jet was all analogue. You can implement a
>> workable EFI system with a 555 and a few op-amps if you approach it
>> correctly. Especially if you only have a limited number of operational
>> states.
>
>Ya, there's no emissions stuff.  We run with a straight pipe and no
>catalytic conv.
>
>The plan right now is to use a microcontroller board (based on Siemens
>167CR) to do everything - where "everything" is a/d converstion of the EGO
>and injector actuation.
>
>An all analog system is certainly intriguing.  I think it'll be easier to
>develop the system with a programable board, but if we get everything
>working before the competition, I'll start looking into a simpler system.

You are going to have a _difficult_ time finding a small enough injector to
run digital !!

How big (displacement) is this one lung engine ?? How many rpm do you plan
to turn it ??
>
>> For reading on economy it is also worth having a read of anything you can
>> find on aviation engine control. As planes in level flight are effectively
>> at a single load point and there is very little qualified in terms of EFi
>> the pilots manually lean the mixtures to get best BSFC, which is not
>> something you can easily do with a car. If I understand it correctly you
>> want to open the throttle whilst leaning the mixture until you reach the
>> lean limit or WOT.
>
>Oo, that's a good suggestion for research.  I think it's applicable... in
>the competition, we open the throttle, get the car to x mph, then kill the
>engine and coast to y mpg, then start the engine and run up to x ... etc.

This is one way to minimize throttling losses ! :-)

Better known in some circles as "Georgia Overdrive" or "Jewish Overdrive" !! :-)
>
>What're BSFC and WOT?

BSFC = Brake Specific Fuel Consumption--the thing you are trying to minimize.

WOT = Wide Open Throttle.



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