Engine Mods Question
 

Okay first off I drive a 1994 GMC Yukon 5.7L
Its an automatic, with currently no modifications, although I was wondering if anyone has a similar engine or knows of experiences with a few mods that I'm wondering about putting on my truck. I just want opinions on each, do you think they will aid in mpg, or some just in power?

The mods consist of the following:
- Cold Air Intake (is my believe that by increasing the quantity of air available to engine and lowering its temperature it makes the engine breath easier and can provide a fuel mileage of 1-2mpg benefit)
- Replace Intake Manifold (have a few friends that swear that if you are getting a better intake you should get a better intake manifold, that it will also increase mpg and power, personally I have no idea, what do you guys think?)
- Throttle Body Spacer (everything I read is split 50/50, but I have a good buddy that swears by them, anyone with a yukon try one?)

- Headers (I'm an engineering designer student, and these make a lot of sense, reducing restriction and back pressure should help mpg and power)
- Straight-Piping (basically reducing the bends and curves as well as lowering the distance from the engine to the end of the exhaust should also help mpg and power)(will also have a pipe coming from each header rather than combining them into one exhaust)
- Glass-Packs (as a form of muffler, I believe that they are the least restrictive therefore should be the most efficient for fuel economy)

Above are the ones that I am looking into immediately, in the groups that I would be purchasing and installing them.

I think you'll find the consensus answer here is to change your air intake to something that feeds the engine with warm air, not cold.

Just cruising around, you don't need anywhere near as much power as your engine is capable of making. Feeding it warm air reduces how much air mass it can pull; to avoid over-rich fuel-air mixtures you get shorter injector pulses. But now your engine is making a bit less power, so you run with a heavier foot on the throttle. With the throttle open wider, you have less pumping losses, so in fact your engine is a bit more efficient in this new, warm-intake operating paradigm.

The other stuff makes perfect sense. Get the gases in more easily, out more easily, it all means less wasted power pushing air around, more power available for pushing YOU around - and isn't that the whole point?

No idea on throttle body spacer. If it's cheap, throw it in there and see what happens? I'll tell you now, you do the mod and post your results, people will read it.

By the way - welcome!

Davyboy - what kind of fuel consumption feedback do you have in your truck? Your garage entry says "custom".

MPGuino?

The reason I ask: mods to you driving style - via instant/average feedback - will net you the largest results, faster.

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Check this thread for a current discussion of many of the issues you're wondering about: http://ecomodder.com/forum/showthrea...ust-10328.html

I wouldn't bother with any of those modifications. They are either going to give you worse mileage (cold air intake) or not much gain at all (intake manifold & exhaust mods) for the amount of cash you're going to plunk down. Seriously look through the 65+ mods list (at the top of the page) and go through there. Those are proven modifications and they will work.

There was a guage that was installed before I bought it which told fuel consumption however it doesn't seem to work(sometimes it gives accurate numbers other times not so much), I am looking to a vacume guage, however I always keep track of fuel consumed vs distance driven

I had a 1990 Suburban, and tried some of that stuff. CAI, headers, free-flow exhaust, K&N filter, fuel line magnet (:rolleyes:)... It made it louder. It might have made it faster, but it was still a suburban (= slow). It didn't help with mpg at all. This was before I did any ecomodding or hypermiling, but I have always checked mpg at the pump.

The throttle body spacer *might* help, by lowering the resonant frequency of the intake. It might help if it improves low-rpm torque and power, since that's where you actually drive.

PaleMelanesian you say there was "no" benefit to mpg?
It just seems strange to me because with my engineering background, it would make sense to me, but thanks for your input, I dunno what to think anymore >.<

There might be a benefit (or a loss) that would show up with controlled testing. I never did that. All I did was drive "normally" and measure when I filled up. There is WAY more variation in that than the mods made, so any change disappeared in the noise.

hey good choice in trucks i have a 93 Yukon.currently i am just using a vacuum gauge to help "teach" me to drive more FE.I plan on deleting the roof rack.
my thoughts on free flow exhaust is more helpful at higher rpm which you should not be doing for FE.plus the louder it is the more your going to rev it up and get on it to hear the cool noice.
make sure it is tuned up and running its best then adjust your driving.i learned alot from the hypermiling tips on here.
btw what milage are you getting?

That's one of those vehicles, that you might as well not worry about mileage.