GM Injection
 

Hi folks. Say, has anyone tried blowin' thru GM throttle body injection? Can it be richened up enough for even low boost? I'd like to get a little more grunt from my 454 pk. up, for towing. I have a good Garrett 7101 from a 671 Jimmy diesel, that should work well. Ideas? Thanks, S.

I'm sure you could blow through a throttle body injection system. However, you probably will only be able to run about 2psi of boost on the stock injectors with the stock rail pressure and a tune.

So, you have two options. Get bigger injectors and a computer to hold the injectors open for the proper amount of time, or get an fmu and use the stock injectors.

The 1st option will allow for a fine tune, better reliability, and the ability to make more power (depending on size of injectors).

The 2nd option is crude. It increases rail pressure depending on the manifold pressure to get more flow through the stock injectors. It is pretty reliable, but crude. I wouldn't run more than about 8psi with an fmu setup. Make sure you have a good pump capable of flowing well at high pressures.

I have a tunable ecu with 95lb/hr injectors on my race car. I'm trying to squeeze all the power I can reliably out of it. It works well but is expensive and takes a good while to fine tune.

I have a fmu on my daily running stock injectors and 7psi. It isn't a power monster, but it knocked 2 seconds off my factory 1/4 mile time. It has been very reliable, pistons still intact.

Don't forget about the ignition side of things though. Fueling needs to be ballpark to make good power. Timing needs to be spot on. Does your truck use vacuum advance or electronic advance?

Thanks for your response. Yes, I figured i'd need bigger injectors, a boost referenced fpr, & maybe an in line pump, if the in tank won't keep up with it, (Megasquirt II if I have to). It's a 94, 454, OBD I, 2 bbl.,electronic advance, knock sensor spark retard, crank angle sensor only. I'm thinkin' 8 or 10 lbs. should be a plenty, been gathering parts for a while. I'm lookin' at mounting it under the fr. corner of the bed on pass. side, plenty of room, & not far from where exh. Ys together. And of course, tryin' to get it done on a shoe string. Thanks much for your reply, S.

I didn't realize the tbi systems only run 13psi of base pressure. Fmus are designed for high pressure fuel systems, so that is probably not an option. I don't think they make larger than stock 454 injectors for tbi. To worsen the situation the factory regulator is not 1:1.

Basically the only way you can reliably boost this rig with the tbi intake manifold is auxiliary injectors and a standalone. Even then you will probably have to run a separate regulator and fuel return to the tank for the auxiliary injectors. I think a better option might be to go with a blow through carb setup. You could run the stock ecu and just retard the distributor a few degrees if you only plan on running 8-10psi.

Hi. Yea, I was afraid it mite be like that, it seems like a step back to go to a carb set up. After mkt. injection to costly. On another turbo site, a guys makin' over 800 hp with mid 70s 525ci Caddy, blowin' thru a Holly. With no other mods, it'll smoke the tires to the cords. I'll admit to being burned out on turboed carbs. My hot rod Karmann Ghia is runnin' a 2 L 914 Porsche motor, with a TDO4 blowin thru a pair of 40mm Dellortos. Makes a ton of power, but constant tuning & jet cleaning. I plan to inject it when I can find the time & money, at the same time. Well anyway, I do enjoy the discourse. Thanks again, S.