Step By Step
The beauty of the TBI fuel delivery isnt in its performance potential but in the amazing driveability it delivers compared to the Quadrajet carburetor that it replaced. Cold-weather starts, high-altitude driving, and even extreme angles like this are no sweat for EFI. Another benefit of the TBI system is that it simplifies the engine compartment by eliminating a ton of vacuum lines, wiring, and emissions band-aids that GM engineers had to use on the 86 carbureted engines to meet federal emissions standards.
If carb guys can stroke their 350s out to a 383ci big-block killer then so can you. The Jan. 2000 issue of Hot Rod featured a 91 350 bored 0.030 over that used a 33/4-inch stroke crank to give them a TBI 383. The long-block was built up using World Products S/R iron cylinder heads with 76cc combustion chambers and 1.6:1 ratio roller rockers. Compression ratio was kept at a relatively low 9.1:1 with hypereutectic pistons from Federal Mogul swung on 5.700-inch connecting rods. Edelbrock supplied the cam and intake manifold, but it took Tom Miller from Turbo City to program a custom PROM chip to get the 383 to even come close to running right. Miller is building a Vortec head TBI 383 that uses the new GM Vortec TBI intake, and a 454 throttle body and injectors that will work with the factory ECM and his custom chip. Does 330 hp and 450 lb-ft of torque sound good? If you want to go any higher than that you will have to add injectors as the 75 lb/hr units for the 454 become the limiting factor.
Performance camshafts for TBI engines are rarely talked about but there are a few out on the market. Because these engines use a manifold absolute pressure (MAP) sensor they are very cranky when they dont get manifold vacuum that is within stock parameters. We called around to a few of the major cam manufacturers to get an idea of what was out there for you to get a little more power.
The engineers at Vortech produce this smog-legal supercharger kit for 90-95 TBI 305-, 350-, and 454ci engines. The gift of boost comes from a centrifugal charger that mounts next to the alternator. Supplemental fuel comes from two new injectors that mount in a plate that is sandwiched between the stock intake manifold and the throttle body. The small-block kit (PN 4GB218-050SQ) blows out 295 hp and 375 lb-ft on the 350. If youve got a big-block (PN 4GC218-090SQ) then you can expect 315 hp and 465 lb-ft to get your heartbeat moving faster. Either kit will set you back $3,708.75. Speeding tickets will cost extra.
How many times have you sat on a trail and waited for a guy with a carbureted engine in front of you to climb that steep or rough section up ahead, only to watch him stall out over and over because his carb keeps flooding out? You know the drill. The guy has to go through the ritual roll back, restart the engine, rev the snot out of it to clear the flood, and then put it in gear to try the obstacle another time. He lines up, gets on the throttle
and stalls again. While youre sitting there sniffing the unburned fuel spewing out of the truck, you are thinking how electronic fuel injection (EFI) was made for us off-roaders.
Sure, people will tell you that fuel injection was invented for cars, and for getting better fuel economy or cleaning up emissions. But the truth is that EFI never shines brighter than it does in our off-road rigs. And thats because we ask our engines to function flawlessly in situations other engines would never see. We go vertical, bounce all around, idle for hours in desert heat, and lug the engine rpm down way too low. EFI is great at doing all these things, and when GM introduced the throttle body injection system (TBI) on its V-8s in 1987, we were immediately spoiled by how forgiving it was even when we abused it. That is until we tried to modify it for more power.
To keep the carb guys from having all the fun we dug up a few engine modifications you can make to keep up with all your four-barrel buddies. Just keep in mind that you cant get too radical with these engines because supplying them with enough fuel and keeping them emissions-legal are huge limitations. Figure 360 hp as the most youre going to get out of a TBI 350. If you want any more than that youll have to move up to a multiport fuel injection system
which is always an option!
World Products Inc.
Sterling Heights, MI 48312