TBI cam duration

[rr]

Walt,

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.

Walter Sherwin wrote:

> >Assuming I can find a 454 tbi, how much hp will it feed without going to
> >bigger injectors or making custom modifications to it?  I'm a "bolt on guy"
> >not a machinist and am just learning ecm.  (I ordered the new board, but it
> >appears it will be a while before I have it up and running).
> >
> >I would appreciate any ideas  on a simple and inexpensive way to keep efi
> and
> >still get 400 hp.
>
> Hi all;
>
> The biggest trick when seeking high HP from a 454 2" TBI unit, is to work on
> the fuel flow capacity offered by the stock TBI injectors.  There is ample
> airflow capacity from the TBI unit, in comparison to the fuel flow
> ............
>
> A typical late model GM 454  (L19) dual 2"  blade TBI unit will be equipped
> with two TBI injectors which will each be engraved with this number
> "17084304".  The dealer service part number for these injectors is 17112560.
> When controlled by a typical GM TBI box, firing in synchronous fashion (ie:
> firing each injector once per every other distributor reference pulse),
> these little guys will squirt about 120'ish  pounds per hour of net fuel
> into the motor at say 5000RPM on a typical V8, at the stock average TBI fuel
> pressure of 10psig differential.  This level of fuel flow will only support
> about 275 naturally aspirated Hp max, BUT,  the available airflow capacity
> of the TBI will easily support 400+ naturally aspirated Hp, if  not hindered
> by the limited fuel flow.   Does one have to give up on the lowly GM 2bbl
> TBI at this point?............No.
>
> If you raise the fuel pressure differential across the injectors, you will
> get more fuel delivery,  roughly in accord with the "square" rule found in
> most hydraulics texts.  One really simple "bolt-on" way of accomplishing
> this is to go to your local GM dealer and order  P/N 17113079.  This is a
> 30psig TBI regulator/meter cover assembly which will bolt directly in place
> of the stock parts found on your TBI unit.  Doing so will give you about
> 220'ish  pounds per hour of net synchronous fuel at around 5000 RPM on the
> same V8 engine, which is roughly enough fuel flow for around 500+ Hp max.
>
> The only drawback is that you must also rescale/reprogram your TBI software
> tables to suit the newfound injector flow.  There are enough "hacks"  of the
> common GM TBI boxes that this should not be an insurmountable problem once a
> basic understanding of TBI/EFI software is  acquired for your application.
> Don't just change single variables like "KNEGRCNST", without  massaging the
> equivalent EGR mass tables, if you wish to retain EGR functionality.
>
> Walt.