Re: 4 BBL Carburator for new Poly Intake
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Re: 4 BBL Carburator for new Poly Intake



Heh, heh, well I feel like the Google translator that is trying to translate Don's experience -- and probably doing a similar quality job. LOL I wish Don was still a member here so he could 2c it out!

Your argument I buy, and the math seems to follow along. 

Here is what Don wrote about his practical carb size formula:

"... the question comes up in one’s mind that carb sizing is for racing of full performance. What if one just wants carb for an engine that will never see 6000 RPM. Should you use a different formula?
Actually it is not necessary. Because carb sizing is focused on the whole rpm range and proper carb operation at low speed. That is because any engine will operate a carb at high speed. That is never a problem, even a 1050 Dominator on a VVW flat four would be possible at 2500 RPM. It is the low speed performance that we are always concerned about and the carb sizing formulas, mine or the complicated math version, are picking the largest size of carb practical that will still drive normally and properly at normal low speed so you can use the same formula even if you intend to drive like yer Granny...." 

Thanks,
Gary H. 

>  -------Original Message-------
 
>  
>  Gary, I'l defer to you, but let's explore this a bit further just for
>  discussion purposes.
>  
>  
>  Don acknowledged his math (CID x 2) was a cheater method given it wouold
>  always end up close anyways to the specific formula of RPM / 2 x CID/1728.
>  However, I interpreted his cheater method in the context of his race motor
>  builds.  Here's how I came to this conclusion - and let's use the Poly 4
>  barrel as an example:
>  
>  
>  DD rule of thumb: 318 x2 = 636 CFM
>  
>  
>  Specific formula, using 7000 RPM as a rev limit for a race engine: 7000 / 2
>  <3500> x 318/1728 <0.184> = 644 CFM
>  
>  
>  => DD method and formula close enough to not be concerned, right?
>  
>  
>  Now ... let's apply the formula to a cruiser, and just for discussion say
>  the shift points are 4500 RPM.  Now we have 4500 / 2 <2250> x 318/1728
>  <0.184> = 414 CFM.
>  
>  
>  My thinking is the RPM is the variable, and really the telltale on a) what
>  kind of driving you will be doing, so b) you can find the sweetspot CFM.
>  
>  
>  Fun stuff...
>  
>  
>  Jim 

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