Throttle Body Spacer and Fuel Economy

[joelorensen]

I've ready mixed reviews on the web, anyone with 4.7L experience as it pertains to increased fuel economy. If it shows an increase, seems like pretty good bang for the buck.

[Johnny_5]

It does NOTHING!

[joelorensen]

Thanks....actually just found a thread here that states the same thing....guess it was just wishful thinking.

[Salty_Dog]

The best way to get better mileage in your Tundra is to keep your engine properly tuned, keep your tires properly inflated, and to ease up on the gas pedal.

There are no magic bolt-ons to improve mileage. If there were, they would have been installed at the factory. Ever wonder why something like a TBS does not come pre-installed? BECAUSE THEY ARE WORTHLESS!

[Highwaylizard]

Ah yes - some contraversy to bring readers back to the MOST AWESOME FORUM Tundra Solutions!!

Seriously, I was getting ready to do a write-up on Throttle Body spacers and why they do not work but also on what does work in terms of mixing or tumbling the intake air. Maybe I can find some time this weekend. Spending most of my days trying to set up the deal of the century so I can retire.

[Highwaylizard]

I've ready mixed reviews on the web, anyone with 4.7L experience as it pertains to increased fuel economy. If it shows an increase, seems like pretty good bang for the buck.

Throttle Body spacers sound good in theory but do not work in practice. Assuming the spacer could impart enough spin on the incoming air to bring it to the level of better blending the A/F mixture it would still have to surmount a few hurdles.

First there is the throttle plate itself. In all but wide open applications this plate is sitting at an angle to the incoming air. This is kind of like having something lodged in your windpipe. The spinning air would have to make it past the throttle plate and maintain that spin into the upper manifold. The amount of spin imparted on the air will be negated by the turbulence created by moving past the angled throttle plate.

Second, let us assume that the air does remain spinning after passing the angled throttle plate. Now that air stream needs to be split into 8 separate paths - and mind you these paths are not continuous flow but rather start and stop spurts. As each cylinder draws air in through the open intake valves air rushes down the intake runner into the cylinder. As it does so it rushes past the fuel injector (HOORAY!!!) which sprays fuel into the passing air stream. Hopefully the fuel is sprayed in rather than squirted as the idea is to have the fuel evenly dispersed in the air stream and not as droplets - as a side note clogged, blocked, or caked injectors result in coalesced fuel droplets rather than an even mist which decreases fuel economy so keep those injectors clean!

Now, back to what is taking place in the intake manifold and runners. The cylinder draws its air and fuel charge and then the intake valves spring shut. The air previously rocketing down the intake runner now slams to a halt. Simply stated, Newton's Third Law encompasses that for every reaction there is an equal and opposite reaction. Ooops. The air bounces off the now closed intake valves and the shock wave travels back up to the intake manifold where it collides with all the other air milling around in there. This is followed immediately and continuously by the air from the other 7 cylinders. Any spinning imparted by a Throttle Body spacer is systematically pummeled to death by the shock waves created when the air being drawn into the cylinders ricochets off the closed intake valves.

For this reason Throttle Body spacers do not provide improved fuel economy. But the story does not end there.

There are ways to tumble the intake air as it enters the cylinders. A few years back I came across "intake tumblers" while researching a theory of mine. Audi did this awhile back by placing adjustable tabs in the intake runners just before the cylinder head. They would adjust according to intake velocity in order to provide the most beneficial mixing of the air and fuel as it entered the cylinder. They had some problems with the set-up and I am not sure if it was ever perfected but the idea is intriguing. It also brings to mind that any tumbling or spinning should be "tuned" to a particular RPM and Throttle Body spacers being a fixed object are unable to react to or adjust to changing intake velocities. If they did work it would only be in a very limited RPM band - probably in the upper extreme RPM range where things got to moving so fast that each intake stroke of each piston would be so fast as to POSSIBLY compensate for the reverse shock wave created by the intake valve closing.

[joelorensen]

Awsome write-up.....it makes very good sense, and allows me to realize that there is a little more going on inside then I was really thinking about.

[Highwaylizard]

Awsome write-up.....it makes very good sense, and allows me to realize that there is a little more going on inside then I was really thinking about.

Thank you - I have been meaning to address this for awhile. Glad you found it helpful.