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formula to work out, how many cfm for tb size 

 

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 Post subject: formula to work out, how many cfm for tb size
Posted: Thu Jan 17, 2008 9:48 pm 
Oompa Loompa
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Does any one know the formula to work outcfm for throttle body size. eg how many cfm will a 70mm throttle body flow?
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Posted: Thu Jan 17, 2008 11:01 pm 
Getting Side Ways
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65 mm is o/k modded street....
70 mm on camed up, high rpm engine...

 

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Posted: Fri Jan 18, 2008 7:37 pm 
Tyre Shredder
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dont know any formula...... spose its just pye r squared - the area of the spindle shaft

in a book ive got it says that 60mm flows 526 cfm 65 =616 cfm 70 =726 75=845 would vary a bit on different brands

hope this helps
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 Post subject: thanks
Posted: Sat Jan 19, 2008 9:19 pm 
Oompa Loompa
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thanks that does help
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Posted: Mon Jan 21, 2008 11:52 pm 
EFI Guru
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That same book also shows MAF flow rates .@28"....
Stock 55mm MAF = 606cfm
Ford Cobra 70mm = 815cfm
Pro-M bullet 75mm = 964cfm
Pro-M 77mm = 1598cfm
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Posted: Mon Jan 21, 2008 11:57 pm 
Getting Side Ways
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XR9UTE wrote:
That same book also shows MAF flow rates .@28"....
Stock 55mm MAF = 606cfm
Ford Cobra 70mm = 815cfm
Pro-M bullet 75mm = 964cfm
Pro-M 77mm = 1598cfm
shows how well matched the ford v8 is,suprised the smaller maf runs so well.

 

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Posted: Tue Jan 22, 2008 11:25 am 
Getting Side Ways
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Don't mean to be a picky little prick but I believe those flow rates would be the tb on its own. What about the rest of the inlet tract pre tb?
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Posted: Tue Jan 22, 2008 12:35 pm 
Tyre Shredder
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how longs a piece of string?.... every model built with different size pipes and angles , filters , airboxes would vary ...you,d have to test each one....if the cross sectional area is greater than the throttle body then it shouldnt be a restriction
the motors just an air pump so you could calculate how much the motor needs at 100% volumetric efficiency by calculating the swept volume of the engine and multiplying it by engine RPM then convert to CFM

then it gives you an idea as to whether intake improvements will work or not
ummm i think thats right :?
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