I have a hard time believing there's anything more to this than hype, based on a few years of studying it in college and what I know from other sources. There was a big push in the 50's to build airplanes with "laminar flow" aerodynamics, meaning NO turbulence - it was a technological dead end, resulting in the Voodoo fighter which, while elegantly sleek, failed to achieve anything that could be qualified as success. ...either in laminar flow or combat! It is, however, a fitting name in the context of this thread, since it proves that there is ALREADY more "swirl" in the airstream of your throttle body than a few 1/16" grooves in the circumference of a phenolic paperweight could ever hope to produce or reduce.
Even if it did create swirl, what effect would that have on the stoichiometry of the combustion chamber? It's at least 12" away in the airflow so any swirl created would die off in the plenum or the runners. And if it reduced the turbulence from the accordion fresh air ducts, it would all come back rushing past the rough interior of the cast aluminum plenum and making all the turns and blasting past the valves. So who is Martin and what is he doing to our dry cleaning? The only thing they're selling is brownie points for guys who think their Chebbies with snazzy paint jobs will dust your Mopar.
Now I'm not saying spacers have NO effect - I don't doubt that having a 1/2" thick piece of plastic GREATLY reduces the heat transferr from the intake to the body of an aluminum carb, lowering the temp of the airstream & reducing the vapor pressure of the fuel in the bowl, but what does that have to do with the price of EFI in China?
The throttle body represents such a small percentage of the surface area the airstream is exposed to that it won't affect Intake Air Temp. significantly. The IAT has no effect on how much fuel is introduced into the combustion chamber (like a carb which is operated by the vacuum it generates). There's no fuel bowl, so the fuel temp. is also unaffected.
The fact that many people buy them doesn't impress me either: many people buy Dominos pizza thinking it's better than the cardboard it's served on; many people buy magnetic "fuel declusterers" that are supposed to break up some mythical clusters in gasoline; many people even buy GM & DC products ([img]/wwwthreads_images/icons/wink.gif[/img]just kiddin'![img]/wwwthreads_images/icons/laugh.gif[/img]). When I find out exactly what the manufacturers think the thing is supposed to do (besides magically drop in 14 HP), I'll reconsider my opinion. Until then, they can keep them on their desks & I'll buy a rabbit's foot.[img]/wwwthreads_images/icons/smile.gif[/img]