TBI cam duration

[Walter Sherwin]

>
>I've wondered about doing this (rasing the fuel pressure). Did
>GM do anything to the new TBI's  to hold the additional pressure
>without leaks? Or, are we safe doing it to the older ones? (89-91)
>
>Thanks for the gm #'s.
>
>BobR.
>




Other than the regulator change, I can't see any significant difference
between the old/new TBI's, in terms of sealing.  Have not yet seen any leaks
at 30psig TBI pressures.

I've operated the 454 "17084304"  (service P/N 17112560)  injector as high
as 70psig on the bench, for extended periods of time.  The bench has a steel
holder block, into which the stock injector and stock upper/lower O-rings
are placed.  Have never observed leaks.  Also, have never observed leaks
even when dead heading the injector against 140psig, during the leak test
procedure built into the bench controller.

One caution specific to "old" 454 TBI's, in the face of increased operating
pressures................check the engraved numbers on the injectors.  If
you have part number "5235231" injectors, then you should replace them with
the part number listed above.  This particular injector seems a bit "iffy"
at 30psig, and deviates from predictable flow quite strikingly at 40+psig.

Here's a couple of other TBI numbers that I've found to be tolerant of
increased pressures................."5235206"  (service P/N 17112493) used
in various 5.7litre TBI applications, good through to 70psig, and gives
around 180'ish pounds per hour each at 30psig....................medium duty
truck TBI injectors (service P/N 17112202) used in all  6.0/6.6litre
governed TBI gas engines, good to around 80psig, and gives around 80 pounds
per hour each at 30 psig or 150 pounds per hour each at 80psig.  The really
cool thing about the medium duty truck injectors is that they are physically
much smaller than the conventional TBI injectors, and they are easy to
package in tight places.

All of the above was with one 4/1 amp peak&hold driver per injector.  To
date, I have not tested any other TBI injectors :(




Walt.