It Howls with small throttle bodies

[Doug Robson]

Stephen Lamb wrote:
> 
> >On Wed, 30 Oct 1996, 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).
> >
> >Ok, to my understanding a "stock" type car has throttle bodies optimized
> >for nice city driving (ie good power down low). Now if you increase this
> >size heaps, the velocity of air in the throttle bodies is very low at low
> >rpm because of the venturi? effect. But at high rpm's the car should have
> >an advantage (along with other mods) of being able to suck in more
> >air/fuel because of the greater tb size (thats what I was saying). I didnt
> >put the 45mm's on, but I want to choke them down a bit to increase low rpm
> >velocity and there fore low speed drivablity. Please correct my if I am
> >wrong. If there is a formula to calculate the size, please say so (the car
> >used to run carbies).
> 
> Jeremy,
> 
> I seem to remember seeing such a formula in the Haynes Weber carby manual.
> Unfortunately I don't have it here in front of me, but will check tonight
> at home and get back.  Of course, this information is for carby's, but
> would still be applicable (right ??...............waits for the avalanche
> of contradictory e-mail)
> 
> BTW, my experience is with Datsun L-series 6's and the general consensus
> with these engines is that the 45's really only begin to work properly on a
> race engine operating mostly high in the rev band.  If you want flexibility
> - and for a street car this is more important (IMHO) - then 40's are the
> way to go.
> 
> Just my 2c (sorry to be a little of topic)
> 
> Cheers
> 
> Stephen Lamb
> Dept. of Defence DSTO, AMRL
> 506 Lorimer Street
> Fishermans Bend  VIC  3207 Australia
> Tel: +61 3 9626 7525
> Fax: +61 3 9626 7089
> 
> IZCC #180
Well im talking about 2 litre twin cam * valve with 200 bhp at 7500

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