[Diy_efi] efi conversion

[Gene Holtzclaw]

Paul, thanks for giving me more to think on. If I understand, there is an 
ECU in a GM 85-88? that has an EPROM which is programable? I'm not a 
programmer, and do not have a laptop. Am I better off with any other maker 
of control units that are adjustable? I once installed a Holly Pro-Injection 
4 on a truck with great success but that was easy as it gets. I'm in a whole 
new ballgame here. I'm much more mechanically inclined than electrical and 
may be getting in over my head. I really do appreciate you helping me learn 
as a child does yet I am willing. I like the idea of using an injector that 
can be upgraded later as I don't want to totally butcher this PI unit should 
I decide to get rid of it.






From: Tlsalt at aol.com
>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] efi conversion
>Date: Mon, 17 Mar 2003 07:36:36 EST
>
>Gene wrote,
>
>  My question is in injector sizing because it seems that fuel pressure and
>timing would be more a factor in conversion than size of injector. Or am I
>over simpifing it? Anyway, as far as controllers are concerned, it looks 
>like
>a GM of a mid 90's v-6 will work and put the leads on the injectors as 
>needed
>to correspond to firing order.
>comments?
>
>Hello Gene,
>
>Either you are over simplifying it or over estimating the intelligence of
>ECU's. To further over simplify, EFI injectors are very different animals
>from your mechanical injection. The amount of fuel they deliver is 
>controlled
>by the pulse width, not the timing or the fuel pressure, which is held at a
>relative constant in most systems.  You need to control the pulse width to
>build the proper fuel curve for your specific engine. The injectors are 
>sized
>so that their duty cycle (on-time in relation to engine cycle) does not
>exceed 85-90% and so that the pulse width at idle is not so short to be
>unstable. Most of the injectors you will find on domestic cars will have 
>the
>same nozzle dimension, physical size is a minor issue. A quick and dirty
>estimate of HP potential is (lbs/hr x #inj x 2 x 0.85). The Ford 5.0
>injectors are usually 19lbs/hr, so 6 of them would be(19x6x2x0.85)=194HP.
>This is probably at the high end of what you could expect from this engine
>NA, but probably insufficient for a turbo.  The same size Ford injectors 
>are
>also available in 24,30 and 36lbs/hr.
>
>I would say it is pretty wishful thinking to expect a EFI system from a
>3-4litre GM engine to have anywhere near the proper fuel curve for a 2.5
>Triumph motor with a very different VE curve. Add a turbo on top of this 
>and
>the probability drops further. You need to be able to hack into the ECU and
>control the injector pulse width.  The best option is to use a programmable
>MAP based ECU, but even then you are probably looking at an injector size
>change and MAP sensor change when you go with a turbo. The nice thing about
>MAP is that you don't need anything (MAF or barn door) in front of your six
>throttles. Even if you could find a system from a same displacement engine,
>with the same # cylinders (2.5 BMW ?),you may be in the ball park, but far
>from ideal.
>
>Your fuel rail idea sounds good cosmetically, but not so good from an EFI
>stand point. The injectors need constant pressure and the rail should be
>designed to minimize fluctuation. That said, there are hard adapters for 
>the
>injector top Orings to connect to your metering unit, the GM blower guys 
>use
>them.  Fuel needs to constantly flow through the rail, exiting through the
>regulator and back to the tank.  There is someone in the UK doing EFI
>conversion on this motor using this manifold, have you seen it?
>
>Paul Saltwick
>
>
>
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