Unless the guy doing the swap didn't know how to tune the carbs 
One of my old race cars, 440 powered Duster that I bracket raced and ran in S/ST was used as a mule for carb size testing by me back in the early 1990s, I started it off with a Hollet 600 D.P. thinking the car would leave harder and react quicker with the smallert carb, back then NHRA Division 7 used the 4 tenths Pro Tree in S/ST and Pro bracket racing. I had bought a tranny with a trans brake in it so that was the reason to try and step up the reaction times. I put 4 or 5 carbs and two different intakes on the car by the end of that year, every time I put a bigger carb on it the car ran quicker and faster It picked up almost .8 ET and 7 or 8 MPH by going from the Hollet 600 D.P. on a TM7 intake to a Holley 1050 CFM Dominator List # 9375 on a Mopar M1 4500 intake My last mule motor, 526 C.I. Bracket race motor, liked the dual 1050 Holley Dominator carbs. a lot comparted to a single 1050 Dominator 
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My experiences have been that you can get to the point where a bigger carb that makes more HP on the dyno actually goes slower than a smaller carb that's more responsive and has better shift recovery.
I've dropped from a Holley 1.562" v downleg carb to the original "950" HP w/ the 1.375" v downleg design and the car picked up .15 in 60-ft, .2 in ET and 2 MPH because the smaller carb simply ran better. Yet on the dyno, they showed virtually identical HP.
Plenty of people on here seem to "always" go faster w/ bigger carbs, but I'm not one of them.
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I lost .2 in going from a 750 Holley to 870 Holley..no other changes ,,just a carb swap at the track...
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OK, here's a thought for you. At my last race at Atco, I was trying to slow my car down, to 10.0 I was running 9.95 to 9.98 lifting early in time trials. I got through the 1st round but had a much better light and passed the slower car by the 1/8th and lifted to just stay ahead and ran a 10.02. Being the idiot that I am, I backed the throttle cable so the secondaries opened about 1/2 way. 2nd round, I passed the car at about 1000' and lifted and did a 10.89 at 110. The 60' improved by .05 while the mph at the 1/8 was down by 2. So in my case, less carb was better (at least that day)
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OK, here's a thought for you. At my last race at Atco, I was trying to slow my car down, to 10.0 I was running 9.95 to 9.98 lifting early in time trials. I got through the 1st round but had a much better light and passed the slower car by the 1/8th and lifted to just stay ahead and ran a 10.02. Being the idiot that I am, I backed the throttle cable so the secondaries opened about 1/2 way. 2nd round, I passed the car at about 1000' and lifted and did a 10.89 at 110. The 60' improved by .05 while the mph at the 1/8 was down by 2. So in my case, less carb was better (at least that day)
This had something to do with why I posted this. As you know when we race at National Trail, I have to slow down to an 11.50. I do have a smaller carb, but have never tested back to back with my 1050. when I did run this smaller carb, I also was running a different combo. I do plan on doing some track testing this spring with the smaller one for the NTR meet later this summer.
As far a street ability. My car has no issues. I wouldn't be afraid to get in it and drive across country. I'd run out of gas money before I got to the Mississippi, but it is what it is. Throttle response ... lets just say that from just above idle (1300rpm) with my foot off of the clutch, I can punch it and it will go sideways with ease. (This is the reason I use for not street racing anymore.)
What intake are you running ? Ron
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Thats great that it has good driveability with the Dominator. What intake are you running ? Ron
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Thats great that it has good driveability with the Dominator. What intake are you running ? Ron
Ron, No dominator. Quick Fuel Q 1050 AN on top of a Victor.
Larry
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For performance I would lean towards the 825 , QF 850 or Proform 850 as a starting carb ,then if I can borrow one try the hp1000 sized carbs - QF950 , Proform 950
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For performance I would lean towards the 825 , QF 850 or Proform 850 as a starting carb ,then if I can borrow one try the hp1000 sized carbs - QF950 , Proform 950
I'm currently running a Quick Fuel Q1050AN.. So you think I will go faster with a smaller carb????
Here's a thought. Isn't it true that a carb will only pass the quantity of air that the engine demands? If so, then putting a larger carb on and tuning it should be the answer and to slow a car down, put a smaller carb on so it can't pass the amount of air that the engine needs. After all, isn't an engine just an air pump? Just thinking out loud, maybe I'm completely out in left field here????????!!!!!!!
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Yes the motor is a pump and will only pass through what the smallest restriction allows , for peak flow . If the carb is the restriction and you increase its size that will help . My example is the heads were the restriction - they had reached max flow and a bigger carb did not help power / flow . Yes a smaller carb can restrict flow and reduce power , as I noted with the hp950 I tried plus the back to back carb test on the dyno with new heads. But remember a smaller carb will often have a better signal and can help the short times ,responsiveness , but give up a bit in the top , this can only be seen on the track not dyno . That is why I start with an 1.40/42 venturi carb for performance use , maximum power .
JMO
Tex
But I take it you like the carb alot that you are running now ? Ron
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... know because I kept thinking you ran a Dominator is why I was wondering how well it runs on the street. Dumb me. I guess because I would like to try a Dominator one day I just assumed you ran one. But I take it you like the carb alot that you are running now ? Ron
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I'd consider pulling timing out of it to get to where you need to be. Much simpler and less expensive way to achieve a specific performance benchmark / E.T. than investing in and learning the tuning curve of a new carb.
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I'd consider pulling timing out of it to get to where you need to be. Much simpler and less expensive way to achieve a specific performance benchmark / E.T. than investing in and learning the tuning curve of a new carb.
I hear ya, and will probably end up doing that, but I don't have to buy a new carb. I already have the smaller carb. I was using it before buying the Quick Fuel. With my set up, changing carbs take about 5 minutes. All hook-ups are the same on both carbs.
Just joking but one day I want to try a 1050 carb. Ron
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There is no "determined size".
The real question is "how much pressure differential do you want at WOT?"
Big carb = weak signal = difficult to tune, big power: 1" WOT vacuum.
Economy car = small carb = excellent response + good mileage: 3" WOT vacuum.
Very complex carbs such as Weber DCOE, Dell'Orto DHLA have good response and signal as low as .5".
Carb CFM is not a fixed number. A 750 only flows 750 is the engine demand produces the Holley test vacuum figure of 1.5 inches of mercury. If the engine produces more vacuum (2" etc.) carb flow increases, and vice versa.
Why does high WOT vacuum reduce power?
#1. pumping loss
#2. the VE is affected by the vacuum reading. No N/A engine has 0 vacuum, which means the maximum VE (absent wave/sonic tuning) is below 100%. Theoretical calculation is
((ATM - WOT loss) ÷ ATM)^.5