Calculating CFM from different TB?
Calculating CFM from different TB?
Hello,
I could of sworn I read a thread about this, but I cant find it. Anyone has knows how to calculate cfm and TB plate area from different throttle bodies. So if we want to convert from a 3 plate TB to a single, two, or quad plate TB we can get the proper sizing.
1)Stock 3rd gen -
2)Stock 2nd Gen TII -
3)48 IDA -
4)55 IDA -
5)E&J TB - 1244 CFM
6)Q45 -
Thanks
I could of sworn I read a thread about this, but I cant find it. Anyone has knows how to calculate cfm and TB plate area from different throttle bodies. So if we want to convert from a 3 plate TB to a single, two, or quad plate TB we can get the proper sizing.
1)Stock 3rd gen -
2)Stock 2nd Gen TII -
3)48 IDA -
4)55 IDA -
5)E&J TB - 1244 CFM
6)Q45 -
Thanks
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 15
From: Perth, WA, OZ
Originally Posted by bumpstart
some basic tech -
multiple throttles may be set up to allow staged throttle ( as in rx7 )
smaller multiple throttles of same area to a large single
may prove more responsive to throttle changes
due to inherent more liner airflow response to tip in throttle movements off idle
( especially in petrol and liquid fuel cars when air velocity is critical )
IE
in a big single TB, a small throttle movement down low can amount to a large change in surface area, and drop in airspeed
- hence mazdas trick to use a single 45mm bore for its primary in rx7
then staged 2 x 45mm secondary, with delay till after that critical throttle position
some direct comparisons of the various common import and aussie TB sizes
will update as i go
top to bottom
circle area =
pi x radius squared
42mm x 4
3.14 x ( 21 x 21 )= 1385 mm2 each
1385 x 4
= 5540 mm2 4 x 42 mm
( bike quads , also aftermarket )
stock FD- 45mm x 1 + ( 50mm x 2 )
3.14 x ( 22.5 x 22.5 ) = 1590 mm2
+
[ 3.14 x ( 25 x 25 ) x 2 ] = 3926mm2
= 5516 mm2 staged throttle body, 1 x 45mm, 2 x 50mm
( suspect cosmo RE also similar )
stock FC- 45 mm x 3
3.14 x ( 22.5 x 22.5 ) = 1590 mm2 each
1590 x 3
= 4770 mm2 staged throttle body, 3 x 45 mm
( s4 and s5 rx7, NA and turbo )
weber type TB 55 mm
3,14 ( 27.5 x 27.5 )
= 2375 mm2 each
2375 x 2
= 4750 mm2 2 x 55mm
( weber type efi TB )
compare the weber 55 TB and the stock unit !!!!!!
( some brands taper down to 50 at flange !!! )
38mm x 4
so each 38 mm diameter = 19 mm radius
3.14 x ( 19 x 19 ) = 1133 mm2 each
1133 x 4
= 4534 mm2 4 x 38 mm
( bike quads , also aftermarket )
75mm x 1
3.14 x ( 37.5 x 37.5 )
= 4416mm2 single 75mm TB
( nissan VH45DE 4.5 v8 )
weber type TB 50 mm
3.14 ( 25 x 25 )
= 1963 mm2 each
1963 x 2
= 3926 mm2 2 x 50mm
( weber type efi TB )
70mm x 1
3.14 x ( 35 x 35 )
= 3847 mm2 single 70 mm TB
( lexus 1UZ-FE v8 4.0 )
65mm x 1
3.14 x ( 32.5 x 32.5 )
= 3316 mm2 single 65 mm TB
( holden Vn V8 5.0 )
64mm x 1
3.14 x ( 32 x 32 )
= 3216 mm2single 64mm TB
( ford EA 3.9 )
45mm x 2
3.14 ( 22.5 x 22.5 )
1590 x 2
= 3180 mm2 2 x 45mm TB
( mazda HC JE 3.0 v6 )
60mm x 1
3.14 x ( 30 x 30 )
= 2826mm2 single 60mm TB
( holden VN v6, toyota 7M , 1JZE-GTE, nissan RB20 , SR20. liberty 2 and 2.2 )
weber , 42 mm chokes
3.14 x ( 21 x 21 )= 1385 mm2 each
1385 x 2
= 2770 mm2 2 x 42 mm choke weber
( about 200 bhp with extend port on a weber )
55mm x 1
3.14 x ( 27.5 x 27.5 )
=2375 mm2 single 55 TB
( mazda BP, holden / nissan RB30 )
weber , 37 mm chokes
3.14 x ( 18.5 x 18.5 )= 1075 mm2 each
1075 x 2
= 2150 mm2 2 x 37 mm choke weber
( about 170 bhp on a extend to bridged motor )
multiple throttles may be set up to allow staged throttle ( as in rx7 )
smaller multiple throttles of same area to a large single
may prove more responsive to throttle changes
due to inherent more liner airflow response to tip in throttle movements off idle
( especially in petrol and liquid fuel cars when air velocity is critical )
IE
in a big single TB, a small throttle movement down low can amount to a large change in surface area, and drop in airspeed
- hence mazdas trick to use a single 45mm bore for its primary in rx7
then staged 2 x 45mm secondary, with delay till after that critical throttle position
some direct comparisons of the various common import and aussie TB sizes
will update as i go
top to bottom
circle area =
pi x radius squared
42mm x 4
3.14 x ( 21 x 21 )= 1385 mm2 each
1385 x 4
= 5540 mm2 4 x 42 mm
( bike quads , also aftermarket )
stock FD- 45mm x 1 + ( 50mm x 2 )
3.14 x ( 22.5 x 22.5 ) = 1590 mm2
+
[ 3.14 x ( 25 x 25 ) x 2 ] = 3926mm2
= 5516 mm2 staged throttle body, 1 x 45mm, 2 x 50mm
( suspect cosmo RE also similar )
stock FC- 45 mm x 3
3.14 x ( 22.5 x 22.5 ) = 1590 mm2 each
1590 x 3
= 4770 mm2 staged throttle body, 3 x 45 mm
( s4 and s5 rx7, NA and turbo )
weber type TB 55 mm
3,14 ( 27.5 x 27.5 )
= 2375 mm2 each
2375 x 2
= 4750 mm2 2 x 55mm
( weber type efi TB )
compare the weber 55 TB and the stock unit !!!!!!
( some brands taper down to 50 at flange !!! )
38mm x 4
so each 38 mm diameter = 19 mm radius
3.14 x ( 19 x 19 ) = 1133 mm2 each
1133 x 4
= 4534 mm2 4 x 38 mm
( bike quads , also aftermarket )
75mm x 1
3.14 x ( 37.5 x 37.5 )
= 4416mm2 single 75mm TB
( nissan VH45DE 4.5 v8 )
weber type TB 50 mm
3.14 ( 25 x 25 )
= 1963 mm2 each
1963 x 2
= 3926 mm2 2 x 50mm
( weber type efi TB )
70mm x 1
3.14 x ( 35 x 35 )
= 3847 mm2 single 70 mm TB
( lexus 1UZ-FE v8 4.0 )
65mm x 1
3.14 x ( 32.5 x 32.5 )
= 3316 mm2 single 65 mm TB
( holden Vn V8 5.0 )
64mm x 1
3.14 x ( 32 x 32 )
= 3216 mm2single 64mm TB
( ford EA 3.9 )
45mm x 2
3.14 ( 22.5 x 22.5 )
1590 x 2
= 3180 mm2 2 x 45mm TB
( mazda HC JE 3.0 v6 )
60mm x 1
3.14 x ( 30 x 30 )
= 2826mm2 single 60mm TB
( holden VN v6, toyota 7M , 1JZE-GTE, nissan RB20 , SR20. liberty 2 and 2.2 )
weber , 42 mm chokes
3.14 x ( 21 x 21 )= 1385 mm2 each
1385 x 2
= 2770 mm2 2 x 42 mm choke weber
( about 200 bhp with extend port on a weber )
55mm x 1
3.14 x ( 27.5 x 27.5 )
=2375 mm2 single 55 TB
( mazda BP, holden / nissan RB30 )
weber , 37 mm chokes
3.14 x ( 18.5 x 18.5 )= 1075 mm2 each
1075 x 2
= 2150 mm2 2 x 37 mm choke weber
( about 170 bhp on a extend to bridged motor )
PS
"holden" is an aussie chev/buick/pontiac
Hey Bumpstart,
Thanks a lot for posting up the equation and doing the math I appreciate it. Let see if I got this right...
Infiniti Q45 90mm Throttle Body
90mm x 1
3.14 x ( 45 x 45 )
= 6379mm2 single 90mm TB
Weber type TB 62 mm
3.14 ( 31 x 31 )
= 2375 mm2 each
3018 x 2
= 6036 mm2 2 x 62mm
Your right about the Weber 55mm TB its a downgrade from the FD throttle body.
Thanks a lot for posting up the equation and doing the math I appreciate it. Let see if I got this right...
Infiniti Q45 90mm Throttle Body
90mm x 1
3.14 x ( 45 x 45 )
= 6379mm2 single 90mm TB
Weber type TB 62 mm
3.14 ( 31 x 31 )
= 2375 mm2 each
3018 x 2
= 6036 mm2 2 x 62mm
Your right about the Weber 55mm TB its a downgrade from the FD throttle body.
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 15
From: Perth, WA, OZ
i have 90 mm throttle as 6362 mm2
and the other weber 62mm TB as 2[( 31 x 31 )x 3.14159265] = 2[3018] =6035mm2
PS where have you sourced a 62mm weber TB from?
largest i know of is 55mm
( and when mated to an ex carb manifold had a 50mm choke size in the manifold entry )
make sure that the weber manifold of choice is not more of a choke than your TB !
and the other weber 62mm TB as 2[( 31 x 31 )x 3.14159265] = 2[3018] =6035mm2
PS where have you sourced a 62mm weber TB from?
largest i know of is 55mm
( and when mated to an ex carb manifold had a 50mm choke size in the manifold entry )
make sure that the weber manifold of choice is not more of a choke than your TB !
i have 90 mm throttle as 6362 mm2
and the other weber 62mm TB as 2[( 31 x 31 )x 3.14159265] = 2[3018] =6035mm2
PS where have you sourced a 62mm weber TB from?
largest i know of is 55mm
( and when mated to an ex carb manifold had a 50mm choke size in the manifold entry )
make sure that the weber manifold of choice is not more of a choke than your TB !
and the other weber 62mm TB as 2[( 31 x 31 )x 3.14159265] = 2[3018] =6035mm2
PS where have you sourced a 62mm weber TB from?
largest i know of is 55mm
( and when mated to an ex carb manifold had a 50mm choke size in the manifold entry )
make sure that the weber manifold of choice is not more of a choke than your TB !
TWM makes 56mm, 58mm, and 62mm TB with four injectors for the rotary at about $836 last I checked.
Lives on the Forum
Joined: Sep 2003
Posts: 5,707
Likes: 6
From: BC, Canada
Keep in mind that with more holes you have adding up to a given area, the more wall area you've got, so the lower it'll flow. So it's not a direct comparison. Also remember that with a 3 bore 13B TB, you've got only the one bore for the primaries, and the other two feed the secondaries, so it's not exactly even.
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^^^^what he said.
I've found on my flow bench that there is really no way to just use an equation and get the exact numbers your looking for. TB design etc will throw any calcs based on area off in the real world. I've seen flow increase of about 30% from a 12% increase in size and well over a 100% increase in flow from a 50% increase in size.
Bigger is not always better. There is no need for a 1200cfm TB on an intake system that can only flow 650cfm. You can actually hurt your power and part throttle response if you go too big.
If you want to send me a few to test I'll post the numbers for the collective. My bench can flow over 800cfm@28" depression, and IIRC about 1370cfm@10". I tested a 90mm TB that came out about 1200 once.
I've found on my flow bench that there is really no way to just use an equation and get the exact numbers your looking for. TB design etc will throw any calcs based on area off in the real world. I've seen flow increase of about 30% from a 12% increase in size and well over a 100% increase in flow from a 50% increase in size.
Bigger is not always better. There is no need for a 1200cfm TB on an intake system that can only flow 650cfm. You can actually hurt your power and part throttle response if you go too big.
If you want to send me a few to test I'll post the numbers for the collective. My bench can flow over 800cfm@28" depression, and IIRC about 1370cfm@10". I tested a 90mm TB that came out about 1200 once.
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Jeff20B
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