Airbox Trumpets

[OB_hayabusa]

I have a question for the engineering minded people on this board. (There seem to be a few)

I noticed that the Air Trumpets for the throttle bodies are made of fairly flexible rubber. Would these not deform at high rpm or big mph when the airbox is pressurised.

I only have experience with V-8 injection trumpets and know that they are shaped perfectly for a smooth airflow and exact lengths. They are made from thin aluminium, not flimsy rubber.

Any thoughts on this topic?

 

[OB_Falconer]

Hmmm. An interesting question, I'll take a stab at it.

The trumpets on your V8 were/are probably tuned to work best at a particular RPM (most likely peak horsepower), and whoever designed them had to assume that at that moment there is no differential air pressure assisting the air down into the carb(s)/fuel injector bodies. The trumpets might provide a very small ram effect at that particular target RPM, but nothing all that remarkable, a couple of % at most I'd guess. At other RPMs, they'll just look pretty.

If they look nice and get you that extra 0.02 seconds which let you win a drag race, hey, why not?

In the circumstance you're thinking of, there is a significant net positive pressure in the airbox, so while it is conceivable (or even likely) that the trumpets are no longer in their ideal shape, the positive pressure in the airbox is still providing far more ram effect than you'd ever see with perfectly tuned trumpets. So therefore it's a non-issue, relative to the gain you're seeing from the ram-air effect.

Has anyone out there seen any claims for how much pressure is seen in the air box at speed? While certainly it's a help, I'll make a guess you have to be moving pretty darned fast (well, fast for anything other than a 'busa) to see much of an effect.

-- Falconer