Throttle Body Spacer

How does a throttle body spacer give you more power? Can somebody explain the theory behind it? What's a good one to use? Can you use it on MPI engines? Thanks.

The idea of the tbody spacer goes back to carburetted engines, when smoothing out the airflow path helped to keep the fuel from pooling in the "corners" when it turned into the the intake runners and into the cylinder head from there. It's the same sort of thing that allows the HO head to make more power - the air flows in more efficiently than in the Renix head.

With "dry" manifold setups (MPFI/TPI,) there is no fuel atomised in the intake airstream to pool anywhere. There is a small benefit, as I understand it, to be gained from the increase in intake volume, but I don't recall it being enough to be worth doing the mod. If you are thinking of some serious power mods, consider a "big valve" head swap from Clifford or Accurate Power, and use a late (HO) head and intake setup to do the swap. Couple that with Mustang SVO injectors and you can really start making some progress. You can really get somewhere if you put a stroked short block underneath that head...

There are a lot of power discussions to be followed on the "strokers" board (groups.yahoo.com/group/strokers) with a larger exposure to the Jeep community (sorry, but we're mainly XJ/MJ here, and strokers is pretty much the entire AMC/Jeep inline six community...)

How much power are you trying to gain?

5-90

It increases the plenum volume and in fact the factory did the same thing in 97 so it must be doing something
I have fitted one to a 98 as well and they still felt benefits. I feel more change when I bored my throttle body myself but already had a spacer and bored that out too to match. The Helical bore on the Poweraid spacer I had does nothing and even on their site they list the same improvements with the spacers that do not have them!
I have all the details on how to make your own as well as boring your own T/B in the how to section.

Ah - THAT was the difference! I was thinking along the lines of the old tunnel ram intakes, but I'd forgotten about the "spiral" bore, or whatever they're calling it this week. Orderly turbulence in the airflow is a good thing if the intake is "wet" for the reasons I stated, but with a "dry" intake it don't matter. I did think there was a slight increase in power due to the intake plenum volume, but do you have any non-advert numbers, Gojeep? I'm just curious...

5-90

Sorry but do not understand your question! "do you have any non-advert numbers, Gojeep?"