Posted: Wed Jul 23, 2008 11:19 am
More info:
Throttle bodies
This topic is still kicked around a lot, here is some data of flow bench numbers of different throttle bodies and manifolds. As stated earlier in this thread above, if the engine's ability to draw more air into the cylinders(the part past the intake valves) is not enough to necessitate a bigger throttle body, you may be losing a huge amount of driveability/tuneability and or wasting money and time fitting something your engine cannot handle. Air flow is a very dark art and not an exact science, most times determined by trial and error. For example, take the case listed below of the weber center section by itself with no end castings which flows 181.5cfm, but with dual port end castings flow is increased to 186cfm. It may seem that in this case the manifold would see less restriction to the outside air by having no end castings at all, but the air is actually channeled through the end castings to give better flow. This is also the case with the Digifant throttle body which flows 393cfm by itself, but with a 3" intake pipe mounted it flows 404cfm.
Ford Throttle Bodies-
Size Make CFM flowed @ 28in. of mercury
60mm Ford 526 cfm
65mm AccuFab 616 cfm
70mm BBK 726 cfm
75mm AccuFab 845 cfm
90mm AccuFab 1190 cfm
90mm AccuFab 1225 cfm
Solex Carbs.-
Solex 30 PICT 2 – no choke assembly
71.8cfm @ 20.4in. of mercury
Solex 28 PICT
64.65cfm @ 20.4in.
Single port manifold
96cfm @ 20.4in.
Weber progressive carb. manifold center section
181.5cfm @ 20.4in.
Weber prog. center section with DP carb. end castings
186cfm @ 20.4in.
Weber prog. center section with ’75 bug EFI end castings
175cfm @ 20.4in.
Watercooled VW Progressive TBs(Rabbit, Golf, etc.):
Early rabbit/scirocco 32/40mm(with insert)
280.76cfm @ 10in. of mercury
Primary only – 51.42cfm @ 20.4in.
Early rabbit/scirocco 36/45mm
349.87cfm @ 10in.
Primary only – 72.59cfm @ 20.4in.
Digifant/post-'85 throttle body 35/52mm
393.2cfm @ 10in.
Primary only – 60.5cfm @ 20.4in.
Digifant throttle body with stock intake pipe
337cfm @ 10in.
Digifant throttle body with 3” intake pipe
404cfm @ 10in.
Late '70s bug throttle body size 45mm
Mexican late model bug throttle body 42mm
Vanagon 1.9 is 45mm, 2.1 is 50mm
Throttle bodies
This topic is still kicked around a lot, here is some data of flow bench numbers of different throttle bodies and manifolds. As stated earlier in this thread above, if the engine's ability to draw more air into the cylinders(the part past the intake valves) is not enough to necessitate a bigger throttle body, you may be losing a huge amount of driveability/tuneability and or wasting money and time fitting something your engine cannot handle. Air flow is a very dark art and not an exact science, most times determined by trial and error. For example, take the case listed below of the weber center section by itself with no end castings which flows 181.5cfm, but with dual port end castings flow is increased to 186cfm. It may seem that in this case the manifold would see less restriction to the outside air by having no end castings at all, but the air is actually channeled through the end castings to give better flow. This is also the case with the Digifant throttle body which flows 393cfm by itself, but with a 3" intake pipe mounted it flows 404cfm.
Ford Throttle Bodies-
Size Make CFM flowed @ 28in. of mercury
60mm Ford 526 cfm
65mm AccuFab 616 cfm
70mm BBK 726 cfm
75mm AccuFab 845 cfm
90mm AccuFab 1190 cfm
90mm AccuFab 1225 cfm
Solex Carbs.-
Solex 30 PICT 2 – no choke assembly
71.8cfm @ 20.4in. of mercury
Solex 28 PICT
64.65cfm @ 20.4in.
Single port manifold
96cfm @ 20.4in.
Weber progressive carb. manifold center section
181.5cfm @ 20.4in.
Weber prog. center section with DP carb. end castings
186cfm @ 20.4in.
Weber prog. center section with ’75 bug EFI end castings
175cfm @ 20.4in.
Watercooled VW Progressive TBs(Rabbit, Golf, etc.):
Early rabbit/scirocco 32/40mm(with insert)
280.76cfm @ 10in. of mercury
Primary only – 51.42cfm @ 20.4in.
Early rabbit/scirocco 36/45mm
349.87cfm @ 10in.
Primary only – 72.59cfm @ 20.4in.
Digifant/post-'85 throttle body 35/52mm
393.2cfm @ 10in.
Primary only – 60.5cfm @ 20.4in.
Digifant throttle body with stock intake pipe
337cfm @ 10in.
Digifant throttle body with 3” intake pipe
404cfm @ 10in.
Late '70s bug throttle body size 45mm
Mexican late model bug throttle body 42mm
Vanagon 1.9 is 45mm, 2.1 is 50mm