[Diy_efi] Throttle body size

[Dave Dahlgren]

I can tell you for sure on a N/A engine if the manifold pressure drop 1.5" Hg at
WOT that the Tbody is  ok if it gets much more than 2.5" at WOT it is too
small.. For all out race stuff with no consideration for tip in performance or
low speed torque 0.75" to 1.00" seems to work well also.
Dave

Eric Byrd wrote:
> 
> The SDS folks I just got done reading from their site say this about
> throttle bodies:  if the vacuum taken off the MAP sensor is higher at
> full throttle than at idle, your throttle body is too small.
> 
> And here is a rule of thumb.  Since flow rate is (density) x (flow area)
> x (flow speed), and since flow resistance in a given kind of obstruction
> depends strongly on flow speed through it, if you know a certain engine
> has a given TB size, and the engine you are looking at is, for example,
> twice as large, then in general, its TB should be larger by a multiple of
> (root)2.  No doubt there are lots of other factors, but I don't know any
> more than that.


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