DIY_EFI Digest V4 #593

[CSH-HQ]

Holley is not rating the CFM of it's TBI's by airflow, as strange as that 
might seem.  They are using a comparitive rating of the injector size 
supplied to average jetting used per carb.  I don't have the exact numbers 
here but like they have 3 TB's all with the same butterflies,, but rate them 
as 650 w/45 lb/hr injectors, 750 has 55's, and the 900 80-90's.  
  All I can say with absolute certainty is that for me, a 355 224 at .050 cam,
9.0:1 CR 3000lb car, with gears and converter luvs 2 (2") butterflies, and 2 
90lb/hr injectors..  
Grumpy




>> 
>> Watch out for the flow on things like Holley Pro-Jection. 2 barrel carbs
>> are rated for flow (in cfm) at 3 inches of Hg pressure drop. 4 barrel carbs
>> are rated for flow at 1.5 in. Hg pressure drop--NOBODY seems to publish the
>> pressure drop at which things like pro-jection are flow rated---BUT--I have
>> talked to folks who have tried the pro-jection, and found, by
>> experience--their engine does _ NOT _ flow nearly as well as with a 4
>> barrel of similar flow rating--that Holley must be rating the projection
>> units at some (unknown) higher pressure drop!!!
>> 
>>  (Just for general info, the multiplier for comparing 2 barrel carbs to 4
>> barrels is .707. A 350 cfm rated 2 barrel only flows 247.5 cfm if rated
>> using the same test conditions which are used for rating a 4 barrel!)
>> 
>> Regards, Greg
>
>Thanks Greg...I had completely forgotten that fact...quite right you are!
>