Do throttle bodies benefit from velocity stacks???

[ecksrash]

I'm working on a modified air cleaner system for use on a type 3. I'm curious to know if throttle bodies benefit from velocity stacks? I see many modern cars that do not have stacks and function very well. I'm running dual 43mm throttle bodies from VW Speed Shop. Thanks for any insight.

[ecksrash]

I imagine that using a dual type throttle body configuration on a VW engine would benefit like a carburetor does by straightening the airflow as it enters into the cylinder head. Any of you dual throttle body users confirm?

[Ol'fogasaurus]

https://en.wikipedia.org/wiki/Velocity_stack

A quick and easy discussion on a long/short subject (pun intended). In the days of the old Hilborn injection the velocity stacks used to reach for the sky and really looked cool but more is known about them and their use now days.

[Piledriver]

Throttle bodies need velocity stacks as a rule, both to smooth airflow and for tuning purposes.
The ones you see with "no stacks" have them effectively built into the air cleaner or such.

The ones typically supplied for Webers etc have such a small bell mouth they are really only useful for tuning, although any transition is better than a sharp squared off edge.

A properly made bell mouth can increase airflow significantly.

The "stacks" on my 42mm ITBs (originally off a FX160 Yamaha jet ski) also have airflow straightening elements in the stacks, like many MAF sensors have, and had a ~4L airbox built into the chassis from the factory.

A central airbox//plenum should be used if possible, several hipo motorcycles out there will lose 15-20HP on the dyno if the airbox is removed to "free up airflow" (`Busas, GSXRs)

[Jadewombat]

Short answer is yes, they would benefit.

I had access to a flow bench years ago and did several tests, PICT carbs, Jetta TBs, etc. Here's the data:

Digifant/post-'85 throttle body 35/52mm
393.2cfm @ 10in.
Primary only – 60.5cfm @ 20.4in.
Digifant throttle body with stock intake pipe
337cfm @ 10in.
Digifant throttle body with 3” intake pipe
404cfm @ 10in.

The top one had no intake pipe on it, the bottom had an oversized one and it flowed more. There's a very dark art to understanding flow characteristics.

[panel]

Good pic to look at for ref........http://www.vvwc.ca/albums/album05/velocity.sized.jpg