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sbnova
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Joined: January 27, 2005
Posts: 741
Location: Lakeland,FL
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 Posted: Thu Sep 08, 2005 6:16 pm Post subject: What is the CFM of popular carbs? |
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I read all about Weber 40's,44's,48's and Dellorto 40's and Kadrons, and Solex's, but what CFM's are some of these capable of? I know swapping venturis changes the flow, so an approximate is fine.
On a side note- I thought I posted this question a few days ago, but I cant find it so I appologize if this is a duplicate post.
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DRD RACING HEADS
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Joined: March 17, 2004
Posts: 440
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| Posted: Sat Sep 10, 2005 4:45 pm Post subject: Re: What is the CFM of popular carbs? |
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I flowed and IDA with a 42mm choke, it was 325 cfm. This will give you and idea. Smaller carbs will be around 225 cfm on up.
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sbnova
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Joined: January 27, 2005
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Location: Lakeland,FL
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stealth67vw
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Joined: January 22, 2004
Posts: 1854
Location: Grass Pants, Orygun
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| Posted: Sun Sep 11, 2005 10:49 am Post subject: |
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Here are few I found over the years:
Source: JayCee Ent./Perf.Tech- flowed on Superflow 600 @25" water
Weber 48mm IDA w/44 venturi-348cfm (per venturi) 1392cfm total
Weber 51.5mm IDA w/47.5 venturi-395cfm (per venturi) 1580cfm total
JayCee 62mm /55 venturi -633cfm (per venturi) 2531cfm total
with 20" water
Holley 1150 Dominator (4 barrel) 1180cfm (est.) total
Weber 48mm IDA w/44 venturi-311cfm (per venturi) 1244cfm total
Weber 51.5mm IDA w/47.5 venturi-353cfm (per venturi) 1413cfm total
JayCee 62mm /55 venturi -565cfm (per venturi) 2260cfm total
Source: Gene Berg Ent. no flow specs given
Weber 48mm IDA 40mm venturi-561 per carb
Weber 48mm IDA 42mm venturi-583 per carb
Source: CB Performance 1991 catalog- no flow specs or venturi sizes
I assume these numbers are @28" H2O per venturi
Dell'Orto 48mm DRLA 388.5cfm
Weber 48mm IDA 372.1cfm
Dell'Orto 45mm DRLA 329.3cfm
Weber 44mm IDF 292.3cfm
Dell'Orto 40mm DRLA 266.4cfm
Weber 40mm IDF 212.8cfm
Dell'Orto 36mm 205.8cfm
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sbnova
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Location: Lakeland,FL
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Bugman Jeff
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Location: Evansville, WI
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| Posted: Mon Sep 12, 2005 12:23 am Post subject: |
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I've often wondered why such a small motor uses so much carb? can anyone explain that to me? I mean, 600 CFM is just right for a mild 350(5.7L) Chevy, yet a 3.0L VW will use 1,200 CFM?
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jamestwo
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| Posted: Mon Sep 12, 2005 5:18 am Post subject: |
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on a V8 with a single plane, each cylinder has full benifit of of all four barrels, on a VW with one ventura per cylinder, each cylinder only draws from one barrel.
So on a V8 with a 65 cfm, each cylinder can draw up to 650 CFM, because only one cylinder draws at a time.
running four 325 cfm venturas on a VW would be the same as running a single 325 cfm carb on a single plane intake. |
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dawi4x4
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Joined: September 06, 2005
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| Posted: Mon Sep 12, 2005 6:15 pm Post subject: |
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my pulling tractor is a chevy 2.3L, demon 1050 cfm
use to run it on my pulling truck 468 ci bbc |
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sbnova
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Location: Lakeland,FL
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A.J.Sims
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Joined: December 11, 2003
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Location: LowBugget.com 982 N Batavia A4 Orange Ca 92867
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| Posted: Tue Sep 13, 2005 5:14 pm Post subject: |
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Stock 40 mm Kadron with 28mm vent and stock aircleaner brackit.
165cfm @25"
Our 46mm Kadrons with 38mm vents and our Air Top kit.
243cfm @25"
Our 48mm Kadron with 42mm vents,Air Top Kit, Spray Bar
307cfm @25" With JC.Ent stack 330cfm @25"
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Terry Cloyd
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Location: Valley Center "SO CAL"
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| Posted: Wed Sep 14, 2005 1:11 pm Post subject: |
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| A stock VW dual port head with 35.5mm intake and 32mm exhaust valves will flow 92.93 cfm with 44s. At .450 lift the head flows 126.35 at .600-in lift the flow is 139.01. Terry |
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vdubyah73
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Joined: July 05, 2003
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Location: somewhere in Texas, my house has wheels
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| Posted: Wed Sep 14, 2005 2:09 pm Post subject: |
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Is this 1 barrel or both?
Weber 44mm IDF 292.3cfm
Thanks Bill |
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stealth67vw
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| Posted: Wed Sep 14, 2005 4:43 pm Post subject: |
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One venturi (barrel)
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John Bates
JB Machining Services
1967 street Bug 2276 w/ 48 IDAs, 2020lbs with driver
7.76 @ 89.55mph 1/8 mile
12.34 and 108.10 mph 1/4 mile |
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vdubyah73
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| Posted: Wed Sep 14, 2005 5:11 pm Post subject: |
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Does that mean I can tell some mook thats raggin' on my 2275 cc dune buggy that I got 1170 cfm worth of carb on my puny little VW engine?  
Thanks, Bill |
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stealth67vw
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| Posted: Wed Sep 14, 2005 6:07 pm Post subject: |
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You sure can 
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John Bates
JB Machining Services
1967 street Bug 2276 w/ 48 IDAs, 2020lbs with driver
7.76 @ 89.55mph 1/8 mile
12.34 and 108.10 mph 1/4 mile |
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RanX0R0X
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Joined: December 22, 2008
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| Posted: Thu Dec 02, 2010 7:10 pm Post subject: |
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| jamestwo wrote: |
on a V8 with a single plane, each cylinder has full benifit of of all four barrels, on a VW with one ventura per cylinder, each cylinder only draws from one barrel.
So on a V8 with a 65 cfm, each cylinder can draw up to 650 CFM, because only one cylinder draws at a time.
running four 325 cfm venturas on a VW would be the same as running a single 325 cfm carb on a single plane intake. |
Yeah, I know, this post was from a long time ago but I'm curious to know how to think about the flow rate.
1 cubic foot/minute = 0.471 947 45 liter/second
Dell'Orto 40mm DRLA
266.4cfm*0.471 947 45
=~125L/second
1914cc/4=478.5cc which thanks to metric
=0.4785L
(2000RPM/2)*0.4785/60 seconds
=~8L/s
Does that look right? |
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VW-Gasser
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Joined: January 30, 2006
Posts: 204
Location: Quincy MA
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| Posted: Thu Dec 02, 2010 9:23 pm Post subject: |
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| stealth67vw wrote: |
Source: CB Performance 1991 catalog- no flow specs or venturi sizes
I assume these numbers are @28" H2O per venturi
Dell'Orto 48mm DRLA 388.5cfm
Weber 48mm IDA 372.1cfm
Dell'Orto 45mm DRLA 329.3cfm
Weber 44mm IDF 292.3cfm
Dell'Orto 40mm DRLA 266.4cfm
Weber 40mm IDF 212.8cfm
Dell'Orto 36mm 205.8cfm |
I am not sure if I read this data right, but it looks like that 48 DRLA are less restrictive than 48IDAs? And does that mean that you can get a little more power out of the DRLA (perhaps the TriJet ones) than out of the IDAs?
Thanks
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modok
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Location: Colorado Springs
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| Posted: Fri Dec 03, 2010 12:53 am Post subject: |
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| RanX0R0X wrote: |
| jamestwo wrote: |
on a V8 with a single plane, each cylinder has full benifit of of all four barrels, on a VW with one ventura per cylinder, each cylinder only draws from one barrel.
So on a V8 with a 65 cfm, each cylinder can draw up to 650 CFM, because only one cylinder draws at a time.
running four 325 cfm venturas on a VW would be the same as running a single 325 cfm carb on a single plane intake. |
Yeah, I know, this post was from a long time ago but I'm curious to know how to think about the flow rate.
1 cubic foot/minute = 0.471 947 45 liter/second
Dell'Orto 40mm DRLA
266.4cfm*0.471 947 45
=~125L/second
1914cc/4=478.5cc which thanks to metric
=0.4785L
(2000RPM/2)*0.4785/60 seconds
=~8L/s
Does that look right? |
Do keep in mind
Holley's carb CFM ratings were usually @ 3mm HG for regulear apps and 1.5mm HG for Hp apps. You can roughly convert 25 inches of water depression CFM to the lower carb CFM rating with a conversion you can probably find somewhere maybe.
I don't know what you are trying to figure out, for IR carbs most everybody just goes by venturi size. To get scientific maybe you could figure the flow coefficient of the vent size?? and use that to compare? |
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RockCrusher
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Joined: August 03, 2010
Posts: 4596
Location: Parkesburg, PA
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| Posted: Fri Dec 03, 2010 1:02 am Post subject: |
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| vdubyah73 wrote: |
Does that mean I can tell some mook thats raggin' on my 2275 cc dune buggy that I got 1170 cfm worth of carb on my puny little VW engine?
Thanks, Bill |
You can....kind of.
Those ratings are based on steady stabilized flow where as we use them in a stop and start mode......kind of. Independent runner applications are far different than plenum apps.
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catbox
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Posts: 869
Location: Portland, Oregon
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| Posted: Fri Dec 03, 2010 9:25 am Post subject: |
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This is good information to have.
I just stepped up to a set of Dell 45's for my new motor and was just wondering what these flow for a comparison to the numbers the head guys put out.
Of course they are probablly not a direct comparison but a comparison anyway. Better than nothing.
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