port injection for 4.3L V6 ?

[Walter Sherwin]

> What is it about CPI that gives it that much of a HP increase?  How much
> of it can be compensated for through careful tuning on the TBI system?  I
> was considering going CPI with my Bravada, but the TBI system is so simple
> and elegant that I really hate to replace it with anything so
> intimidating-looking :)
>
>  On Fri, 13 Jul 2001, Charles Morgan wrote:
>
> > Howells used to sell a kit to retrofit 4.3Ls with TBI to Central Port
> > Injection.  CPI is not really port injection, though it does have
pressure
> > operated poppet valves at each port.  Horsepower is increased from 160
(for
> > TBI) to 200 and peak torque, I believe, is 260 lb ft.  CPI manifolds are
> > listed on Ebay every now-and-again--I think there's one there now.
> >
> > Charles Morgan
> >




There may well be some base engine differences between the two benchmarks
listed above, that makeup the delta's.  IMHO I would stay far away from a
CPI conversion.  The 4.3 CPI spider unit is the goofiest/dribbliest thing
that I've ever played with on the wet flow bench.  Fun to watch, but I can't
imagine what they were thinking.  Even GM gave up on it after a few years,
and in turn went to sequential CPI (aka SCPI).  Warranty and customer
satisfaction were awful for CPI, and a bit improved for SCPI.  You'll note
that all of GM's recent product offerings are now PFI.  Both CPI and SCPI
fall far short of of a basic/good  PFI setup, no matter what yardstick you
use (except perhaps the bean counters' yardstick......but then you have to
install the special myopic glasses so as to understand the rationale).  For
all round truck use, an optimized & well calibrated TBI setup is pretty hard
to beat and very little would be gained by going PFI.

The problem is that most people have, at first thought,  junked the TBI
hardware in favour of the more sexy stuff.  Within the realm of TBI stuff,
you've got OE hardware that came on everything from wheezy 4-bangers to
throttled 454's.  With some tinkering, you can get almost anywhere you want
in terms of HP with TBI.  A BBC 2bbl dual 2" TBI, for example,  can be made
to support about 450+ Hp with the aid of near stock OE software.  Optimize
what you've got on your 4.3, enlarge the TBI blade area and injector flow as
required, get a good manifold, and watch/tune your fuel pressure as
described here ....  http://www.aces.edu/~gparmer/efi/tbi_adjust.htm ).
You'll have a lot of fun........


Walt.


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