Re: Carb CFM
[Re: 1970RT]
#2546104
09/05/18 12:02 PM
09/05/18 12:02 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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If its just for racing then think big.. I had a 405ci and had a 1050 dom on it and wanted to put a 1150 on it but sold the engine
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Re: Carb CFM
[Re: 1970RT]
#2546144
09/05/18 01:32 PM
09/05/18 01:32 PM
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Joined: Aug 2003
Posts: 43,252 Bend,OR USA
Cab_Burge
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Bend,OR USA
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If your racing it or looking for the most power and torque on the engine dyno sheets, bigger is better The difference in head flow, cam LSA, actual rocker ratio and other parts have a direct effect on the engines ability to consume and use the air and fuel the carb allows into them If your after the best mileage and street performance then think small primaries on the carb. Years ago I did some carb size testing at the track on a 440 bracket race motor with a set of mild 906 iron heads and a big solid roller SS cam, it ran faster and quicker ET with the biggest carbs and intake I could put on it, I had assumed that by using a Holley 600 D.P. the car would 60 ft. better and get better reaction times and 60 ft. better, it didn't Every time I put a bigger carb . on the same intake it went faster and quicker Theory and results are not always the same
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Carb CFM
[Re: 1970RT]
#2546151
09/05/18 01:48 PM
09/05/18 01:48 PM
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Joined: Jan 2003
Posts: 11,723 Portage,michigan
B3422W5
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I Live Here
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Portage,michigan
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Most formulas to determine correct size use rpm and cubic inch. That said it generally isnt accurate. I have found bigger is always better in a race car application. I had a hot 318 motor that ran a tenth better with a 950 than it did with two different 750’s i tried on it, as an example
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight 418 BPE factory replacement headed stroker, 565 lift solid cam Best so far, low 10.30’s 1/4 1.41 best 60 foot 6.56 at 104.17
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Re: Carb CFM
[Re: 1970RT]
#2546162
09/05/18 02:16 PM
09/05/18 02:16 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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It also makes a difference if you are using a trans brake.. if you are then use a little smaller carb and the car will leave better off the line due to lower RPMs
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Re: Carb CFM
[Re: 1970RT]
#2546168
09/05/18 02:25 PM
09/05/18 02:25 PM
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Joined: Jul 2004
Posts: 19,318 State of confusion
Thumperdart
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I Live Here
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State of confusion
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Several factors come into play for ME personally, street or strip or BOTH. Heads, fuel,cam,converter, gears,shift points, weight altitude etc........I'm one of the few who never use a calculator to determine these things and I do real world street and track testing so the COMBO tells me what carb will work best for that application............
Last edited by Thumperdart; 09/05/18 02:26 PM.
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Carb CFM
[Re: MR_P_BODY]
#2546181
09/05/18 02:35 PM
09/05/18 02:35 PM
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Joined: Jan 2003
Posts: 11,723 Portage,michigan
B3422W5
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I Live Here
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It also makes a difference if you are using a trans brake.. if you are then use a little smaller carb and the car will leave better off the line due to lower RPMs Not sure what you mean When i used a brake i had 2 step set at 4300 Off foot i left at 2k, so way lower Car 60 footed identically either way( as it should)
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight 418 BPE factory replacement headed stroker, 565 lift solid cam Best so far, low 10.30’s 1/4 1.41 best 60 foot 6.56 at 104.17
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Re: Carb CFM
[Re: Cab_Burge]
#2546293
09/05/18 05:37 PM
09/05/18 05:37 PM
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Joined: Mar 2005
Posts: 939 Metro Detroit
1970RT
OP
super stock
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OP
super stock
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Metro Detroit
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If your after the best mileage and street performance then think small primaries on the carb. I'd like to get the best mileage I can. I know that in speaking of muscle cars, mileage is usually not a concern but I am not concerned with how fast I can go anymore. I'm planning on changing the rear gear to a 3.23 from the current 3.91 that is in it and thought a smaller carb. would help as well as long as it won't affect how well the engine runs (not speedwise but just general operating performance). What I have is a pretty much stock 67 440 HP engine except that when the previous owner rebuilt it, he installed lower compression pistons. I don't know exactly what the ratio is but I think it is about 9:1 or thereabouts based on what he told me. The engine currently has a 750 Edelbrock 1411 carb on it and I'd like to replace it with a lower cfm carb. if possible. Would a carb in the 600-650 cfm range be enough carburation or would that be too small for my 440?
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Re: Carb CFM
[Re: 1970RT]
#2546296
09/05/18 05:40 PM
09/05/18 05:40 PM
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Joined: Jan 2003
Posts: 31,056 Oregon
AndyF
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Oregon
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Is there a formula or some method (other than actually trying different carbs.) of determining what size carb. cfm would be best suited for your engine based on how your engine is built? Some people get confused over how much air the engine needs and how big the carb should be. If you know how much power the engine is going to make then you can calculate how much air the engine will consume to make that power. For example, a 600 hp engine will consume roughly 850 cfm of air at peak power. So that is the easy part, the harder decision is what size carb to buy. Obviously a 850 carb would work but so would a 650, 750, 950 or 1050. The different carbs will work differently with the smaller carbs working better at low speeds while the bigger ones are better at WOT. So the answer is "it depends" which is the same answer to most of the questions on here. You would need to provide some specifics on the car and engine and how you are planning to use it to get a better answer.
Last edited by AndyF; 09/05/18 05:42 PM.
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Re: Carb CFM
[Re: 1970RT]
#2546298
09/05/18 05:44 PM
09/05/18 05:44 PM
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Joined: Jan 2003
Posts: 31,056 Oregon
AndyF
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I Win
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Oregon
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For your application the 750 would work but a slightly smaller carb might work even better. The factory used 600 cfm carbs on a lot of 440 engines. A 400 hp engine only uses 560 cfm at peak power so a 600 cfm carb works just fine on a street driven 440. 90% of street driving is at part throttle anyway.
Last edited by AndyF; 09/05/18 05:46 PM.
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Re: Carb CFM
[Re: B3422W5]
#2546304
09/05/18 06:00 PM
09/05/18 06:00 PM
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Joined: Jan 2003
Posts: 25,903 Rio Linda, CA
John_Kunkel
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Posts: 25,903
Rio Linda, CA
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Most formulas to determine correct size use rpm and cubic inch. That said it generally isnt accurate. But they can be if you know, for sure, what the engine's volumetric efficiency is. It is possible for a normally aspirated engine to attain better than 100% volumetric efficiency.
The INTERNET, the MISinformation superhighway
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Re: Carb CFM
[Re: 1970RT]
#2546314
09/05/18 06:29 PM
09/05/18 06:29 PM
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Joined: Jan 2003
Posts: 14,506 So. Burlington, Vt.
fast68plymouth
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So. Burlington, Vt.
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If you’re looking for better economy, try the new Edelbrock avs2 650 or one of the Street Demons.
I’m not sure how much better the mileage would have to be to justify buying a new carb, but imo if it improved the mileage by 1-2mpg....... you’d be doing pretty good.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Carb CFM
[Re: 1970RT]
#2546371
09/05/18 08:30 PM
09/05/18 08:30 PM
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Joined: Aug 2003
Posts: 43,252 Bend,OR USA
Cab_Burge
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I Win
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Bend,OR USA
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Last edited by Cab_Burge; 09/05/18 08:31 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Carb CFM
[Re: Cab_Burge]
#2546400
09/05/18 09:38 PM
09/05/18 09:38 PM
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Joined: Feb 2005
Posts: 4,318 Prospect, PA
BSB67
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master
Joined: Feb 2005
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Prospect, PA
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On your deal I would look at a Thermoquad or Quadrajet type carb. to get the small primaries with the larger CFM rating at WOT, you will need the correct intake manifold(stock 1972 and later 440 intake This. I have an 800 CFM Holley spreadbore carb on a factory cast iron intake that is my go to combo. The carb has been attached to the intake for the last 25 years and I use it on my stuff or loan it our for others to use because it runs so beautifully on stockish 440s. Then I wrap it back up and put it back into storage until the next guy needs it. Throttle response is great, mileage is better, and power is as good as anything except a 6 bbl.
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Re: Carb CFM
[Re: lewtot184]
#2546530
09/06/18 02:45 AM
09/06/18 02:45 AM
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Joined: May 2003
Posts: 13,202 aZLiViN
J_BODY
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I Live Here
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Posts: 13,202
aZLiViN
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i don't get lost in cfm ratings and don't use them as a major criteria for carb(s) selection. i'm old school and still look at venturi area. So how much would a 1.48 venturi 1.79 throttle blade carb support..... asking for a friend
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