Re: Ok carb size

[Skagdrager@xxxxxxx]

Don,
If you bore and stroke your 318 poly out to 400+ cubes, would you still use 
an 800 or is there an amendment to the formula in this case?
Thanks for all your great info.
Paul
 
 
In a message dated 5/8/07 5:40:12 AM Pacific Daylight Time, 
big-d@xxxxxxxxxxxx writes:

You can do the 17268 cu in thing and divide and mutiply or you can apply 
Don's law which states practical carb size in CFMs is double the cubic inches.
ie a 318 needs 318 X 2 which is 636 cfm so a 650 would be perfect  for a 
screamer and a 600 for a grunter (truck etc)
a 440 needs then 880 cfm so a 850 would do in a heavy vehile and a modified 
850 with choke removed or 870 would be great for a screamer 
A 383 would need a 766 so a 750 would be great for a grunter and a modified 
750 choke removed etc for a screamer.
A 400 would obviously use a 800 and I equipped the Lemans project 400 cu in  
engine with exactly that  producing over 500 hp in streetable trim. 
HOWEVER when you go to a ram style manifold  you can use two of the same 
since the signal a carb gets from this type of manifold is very strong so the low 
speed lazynesss associated with oversize carbs is not there.Also Crossrams use 
vacuum secondaries. (AFB are essentially vacuum secondaries although 
technically they do not use vacuum but air volume to tople the weighted uper 
secondaryair vavle the effect is thesame ( which is to say no airflow in the secondary 
till the engine can sustain it.)Orwe could put it like this i. the car 
operates normaly on a 750 cfm carb (primary side of two 750s which would = 1/2 the 
total volume of the two carbs) When the engine reaches sufficient RPMand load to 
open the secondaries it now has 1500 CFM availble. Vacuum secondaries area 
real boost to street performance vehilces because ofthis. best of both worlds. 
Now if you are a stickler and cant deal withthe Dons law thing then get your 
slide rule out and knock yourself out with the math figuring half (because the 
intake stroke occurs every SECOND revolution)the RPM X cu inches divided by 
1728 (cubic foot in inches ) however i must warn you you wil be picking the 
same size carb when you are done. 
Don
I am getting too old for all this math stuff!!!
Author of
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Old Reliable (Mopar)
http://altonapublicschool.faithweb.com/





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