I ran across some information on a truck site about a throttle body insert made by vararam. It is supposed to increase power and mpg's. The user had good results using it and it didn't sound like he was trying sell it. The company doesn't make one that will fit my 4.3L engine. So in my quest for better economy, etc. I 'm asking for input from members on recommendations and most of all actual experiences with this type of device. I can't use a throttle body spacer due to space limitations.
I think stacks or "throttle body spacers" are more for performance than anything... and yes, some manufacturers had spacers on their designs. [At work] My 460ci Fords that are run on LPG use a 7/8" carb spacer... the engine runs like complete crap w/o it. I don't claim to understand or know why.
I have heard that the spacers worked really well with carburated engines but don't really have any affect on fuel injected ones. there are some that claim otherwise. I am in the same boat as project84, I don't really know enough about them to know either way.
if it is a tornado (or like device) that swirls air, yea, it's crap.
Be the change you wish to see in the world
For carburated vehicles there all lots of atomization enhancers. When I built a Chevy 350 for FE, I used intake manifold gaskets that had a mesh across the openings toaid in this. I don't know if/ how much they worked, but my mileage went up after several bolt-ons, from about 16mpg, to about 21. However, with fuel injection, I haven't seen anything convincing as far as furthering atomization, except maybe "turbulators" (tiny dimples, or bumps) in the runner between the injector, and combustion chamber.
Once installed NO2 kit on a 350 Camaro ('76). Installed the carb spacer which contained the NO2 and gas spray nozzles first, then stopped for the night. Driving the car with this spacer (only) installed definately made a noticable difference. The spacer was about 1" thick. Have seen spacers for sale without the holes drilled and tapped in the side for spray nozzles, meaning that they are meant to be used as stand-alone, no NO2 involved. Dont know anything (good or not) about installing spacers on an injection system, but maybe will try.
My truck (2001 1500 Sierra, 4.8. 4-speed auto, flare side, 3" cat-back duals) gets lousy mileage (around 14 mpg at highway speeds) and am trying to find ways to inprove this. Used to have a '57 Chevy convert., with bored 283
(301 c.i.), Corvette cam, solid lifters and duals (not cat-back) which got 26.5 mpg on the highway when driven gently, but at highway speeds. Don't forget our Canadian (imperial) gallon is 20% bigger than US gallon. Surely similar mileage on a much more sophisticated engine of about the same size should be possible.
One problem - putting 10%ethyl alcohol in gasoline ruduces mileage slightly.
The throttle body spacer will NOT work on your 2001 GMC.
It worked on your 1976 Camaro because it helped with fuel atomization by giving the fuel more time and space in which to mix with the air. It would also work on engines with throttle body injection.
Your 4.8 has injection in the intake manifold, right near the valves, and the throttle body only conducts air.
14mpg highway is pretty awful for that truck. If I'm driving all highway in my 2002 GMC Sierra 5.3 extended cab 4x4 I get closer to 20MPG. I recommend starting a thread describing your truck (including rear end ratio and any more mods than the exhaust).