dual GM TBIs [Fwd: CFM numbers]

[Shannen Durphey]

Actually, I asked this question of many sources.  Most were more
detailed, and most got no answer. (Turbo City replied to say they
consider the information "proprietary").  This one was a long shot,
and so little effort was put into it.

That said, I'd guess it's rated at 3" Hg.  I looked through my
Rochester carb book and compared two barrel carb throttle bore sizes
to CFM ratings, then looked at a 305 cid TB and checked throttle
bore.  That would make this a psuedo-scientific WAG.

Shannen

Greg Hermann wrote:
> 
> >> Dear Sir:
> >>
> >> I am wondering if you know, or can point me toward a source for, cfm
> >> ratings for GM tbi units.  I haven't been able to find them anywhere.
> >> Thank you.
> >>
> >> Shannen Durphey
> >> shannen at mcn.netShannen,
> >
> >        My apologies for the delay. The GM tbi units are not rated by cfm
> >numbers but by displacement size of engines. 4.3, 5.0, 5.7, and 7.4 etc.
> >        Although the 4.3 to 5.7 is approx 465-500cfm and the 7.4 is
> >approx. 550-670 cfm.
> >
> >                                REP. Troy Brown
> >                                Howell Engine Developments Inc.
> >                                6201 Industrial Way
> >                                Marine City, MI 48039
> >                                (810)765-5100
> 
> Hey neat--now--are these (approximate) ratings based on 3 in Hg, (pressure
> drop) like all two barrel carbs are, or on 1.5 in Hg like four barrels
> are??? I believe that Holley, for one, rates their two and four barrel
> Pro-Jection units on the two different standards. (All you gotta do is
> multiply one by .707 to get the other.) Just wonderin' and askin'!
> 
> Regards, Greg