Newbie questions

[steve ravet]

Jim Yeagley wrote:
> 
> EFI gurus,
> 
> I've been lurking her for a while, soaking it in.  My EFI project is a 1975
> Pontiac Grandville, 400 cid.  The car is a convertible that sits around a
> lot here in northern Ohio, so I started thinking about injection a couple
> years ago to avoid all the carb problems that come from sitting.  It wasn't
> until I found this list that I knew it would be possible.
> 
> I would like to use a GM TBI system, say from a Chevy Caprice or truck,
> since I've had a little experience a few years back with GM computers.
> 
> Now for the questions.
> 
> What (if any) is the difference between Chevy car systems and truck systems?
> If I use a  late model Ford fuel pump, frame mounted, is the regulator in
> the throttle body?
> Will a 305 throttle body have enough cfm for my 400?

I think most GM TBI systems have the regulator in the throttle body. 
Frame mounte pump should be OK as long as it's the right pressure (about
15 psi for TBI, 40 or more for TPI).

As far as 305 throttle body goes....  I'm far from an expert but this is
what I've read that makes sense.  A 305 throttle body probably flows
enough air for your 400 but the injectors won't be big enough.  Carbs
have to be sized to the engine so that flow velocity is high enough for
the venturies to work.  EFI doesn't have that constraint so throttle
bodies are sized larger to flow plenty of air.  Flow rate of an EFI
throttle body has more to do with the injectors installed in it that the
physical size.

> 
> I've been reading here about different software/hardware for communicating
> with the car's computer, but I admit I haven't been able to pick up much.  I
> have a little experience with OTC Monitor 2000 and 4000, but they couldn't
> change any settings.  Can someone explain the basic idea behind changing
> (and figuring out the changes needed) the prom?

If you go to the DIY_EFI WWW page and check out the programming 101
project and the tuning tips you'll read about how to make changes to the
EPROM.  Basically the EPROM is chock full of tables that relate VE to
MAP and RPM, tables for timing, tables for temp correction and a
bazillion other things.  Once you know where the tables are and what the
units of the numbers in the table are, you can start changing them to
match your engine.

> >From what I can tell, there's a program that allows you to hook up a laptop,
> kind of intercept the signals and change them between the cars computer and
> the engine, test the changes, then save them.  Does this sound right?  Then,
> how do you get these changes into a new prom?

Aftermarket systems may be that flexible, but not the ones that we talk
about, like 747, 730, 165, etc.  The only way to program them is to
remove the prom, edit the image, and burn a new prom.

> 
> Geez, that's enough for now.  Thanks for your patience and answers, or at
> the least the entertainment from reading all the posts to this list.
> 
> Jim Yeagley

-- 
Steve Ravet
ARM, INC
steve.ravet at arm.com
www.arm.com