Re: Ok carb size

["Ben Jr. Morgan" <polara_hotrods@xxxxxxx>]

So then how come a 750 was drowning my 383 unless I was running all out all the time??? (mild performance cam, M1 intake)
  ----- Original Message ----- 
  From: Don Dulmage<mailto:big-d@xxxxxxxxxxxx> 
  To: 1962to1965mopars@xxxxxxxxxx<mailto:1962to1965mopars@xxxxxxxxxx> 
  Sent: Tuesday, May 08, 2007 5:01 AM
  Subject: Ok carb size




  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!!!
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Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
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