Throttle Body Size

[Chuck Tomlinson]

> From: Mazda Ebrahimi <kleenair at ix.netcom.com>
> 
> Does anyone have a rule of thumb formula for determining throttle bore 
> diameter based on air flow or horsepower data?  I realize I can go 
> around and measure this on various vehicles and come up with a 
> reasonable formula, but I want to know if there is any generally 
> accepted formula.

Based on a glance at some US cars, I'd try:

TB_Diameter(mm) = SQRT( Horsepower / TB_Blades ) * 4.25

This seems to work for naturally aspirated cars with a single- or dual-
blade throttle body and a common plenum.

Give it a try.
--
Chuck Tomlinson