It Howls with small throttle bodies

[Doug Robson]

Todd Knighton wrote:
> 
> tom cloud wrote:
> 
> > Now I'm confused....  With my limited knowledge and cranial ability,
> > I thought that throttle size had little effect on FI.  I can see that
> > a larger TB gives less velocity and therefore less momentum and
> > mixture of the fuel/air, but can anyone 'splain to this ole boy
> > how to determine a TB size (talking normally aspirated).
> 
> Tom,
>         There was a really good article just recently in a motorcycle magazine
> that was specifically about this.  They were talking to Mr X from
> Cosworth about port sizing and manifolds, and according to them, the
> port sizing was all about a specific port velocity to be obtained at a
> specific rpm.  Though we calc'd some of the numbers backwards to a
> street oem 911 Carrera engine, and his velocities dictate that Porsche's
> ports are about 30% too large.  Maybe their independent runner, short
> stacked, 14,000 rpm v8's work differently from 7,000 rpm plenum
> chambered flat six's.
>         About the most interesting thing in the whole article was in reference
> to stacks.  They proved that an intake runner with any more than about
> .5 degrees taper, yup that's a 1/2, significantly decreased the flow.  I
> guess that doesn't say much for carbs, jeez they go big, then small,
> then up and around, then small, then big again.
>         Be careful about your throttle body sizes when referencing them,
> because it makes a huge difference if you have a single throttle per
> cylinder, or two cylinders per throttle, or even 8 cylinders feeding a
> plenum with 4 throttle plates, they're very different worlds.
> 
> Todd Knighton
> Protomotive Engineering

Well interesting you say about taper because when i had the 50mm
throttle bodies my inlet port is 41mm, now with 45 this would reduce the
taper signifcantly

regards

-- 
|===============================================================|
|			When I die, 				|
|         I want to go in my sleep, like my grandfather, 	|
|          not screaming like the passengers in his car. 	|	
|---------------------------------------------------------------|
|  	Doug Robson     (H)	   mailto:doug at cia.com.au	|
|			(W)	   mailto:Doug.Robson at chase.com	|
|    Sydney, Australia		 http://www.cia.com.au/doug	|
|---------------------------------------------------------------|
|    Club Car Racing Register of NSW	    |	Thank God	|
|  1992/93 Under 2 litre State Champion	    |	   for		|
| http://www.cia.com.au/doug/ccrrnsw.html   |	Gravity		|
|===============================================================|