Picking Carb Size: 950, 1000, or 1050 CFM?

Which Quickfuel Carb?

  • QFT 950

    Votes: 4 50.0%

  • QFT 1000

    Votes: 1 12.5%

  • QFT 1050

    Votes: 1 12.5%

  • Other (In comments)

    Votes: 2 25.0%
  • Total voters
    8
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ToMang07

ToMang07

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So without getting into the entire build, motor (440 bored .040 over and decked) will be balanced, and set up with all ARP hardware, windage tray, 6qt pan and std Melling oil pump, stealth heads, roller rockers, porting, etc.

Cam is CCA-CL23-233-4, Basic Operating RPM Range: 3,200-7,000.
Intake is Victor, Basic Operating RPM Range: 3,500-7,500.
Rods are Eagle H-Beam, 850HP rated and Advertised RPM Rating: 7,500 rpm.

So I plan on being able to (not frequently, but due to a 4-speed and very low gears) spin it up to 7,000 rpms.

I have all but decided on Quick Fuel carbs. Yes, I know they are now owned by Holley, but the overall responses I have gotten about carbs AND from what I have seen on successful builds, Seems the way to go for me.

When running CFM calculators, most frequent estimates are 750-850 CFM for street, 900-1000 CFM for "Race/Track". Summit and Speedmaster calculators both seem to agree on this.

Summit:
Street Carb CFM : 767.85
Racing Carb CFM : 993.69

Speedmaster:
Street Carb CFM : 769.57
Racing Carb CFM : 995.92

So I guess my long overdue question is, what are you running, and what would you recommend? I'd rather over-fuel that under-fuel, mileage is NOT important to me, however I don't want to be washing the cylinders out, either.
 
A fairly competent guy with a calculator should be able to figure out the cubic feet of an engine, find the revolutions per minute and decide how many cubic feet of air they need to keep the engine fed. You'd be surprised(probably not) at how many people over carburete their engines and bog off the line.
 
Excellent choice I've been running a Quick Fuel 850 on my smallblocks BEST carb. I ever bought..with your combo I'd go 950..
 
Leadfoot said:
A fairly competent guy with a calculator should be able to figure out the cubic feet of an engine, find the revolutions per minute and decide how many cubic feet of air they need to keep the engine fed. You'd be surprised(probably not) at how many people over carburete their engines and bog off the line.
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Uh... ok. Already used multiple calculators, as stated. Wasn't asking for help there.
 
however I don't want to be washing the cylinders out, either
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OMG! Really?!?!?!

If your washing down your cylinders, that jus means you have no freaking clue how to tune a carb. Size of the carb has ZERO bearing on that issue.
 
I run a 950 on mine. You have more cam than I do in my 440. Not sure of what heads you're running. I'd at least run a 950. If you are running stock heads or eddy RPMs's tat are untouched I would not go smaller than a 950 on that. Mine responds like cracking a whip.
 
oldkimmer said:
I ran a QF 750 on my 470 stroker for awhile. 10.51 at 126.5 mph. Went to a 1000 10.37 at 129.65mph. 74 duster 3300 lbs. Kim.
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My engine builder has always said that mopars restriction is the port and valve. They do not like restriction on top. I've seen this confirmed on my own stuff and on other dyno mills over and over and over. and you just proved it again.
 
roccodart440 said:
I run a 950 on mine. You have more cam than I do in my 440. Not sure of what heads you're running. I'd at least run a 950. If you are running stock heads or eddy RPMs's tat are untouched I would not go smaller than a 950 on that. Mine responds like cracking a whip.
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Stealth Heads port matched and polished.
 
For almost the same cash you can call BLP and get a custom carb.

You should buy you carb based on Venturi diameter and NOT claimed airflow.
 
So I plan on being able to (not frequently, but due to a 4-speed and very low gears) spin it up to 7,000 rpms.
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It sounds like this is a street machine.And a manual trans is a special case.

Any 4bbl will rev to 7000 on that engine, on the street.
Even with 4.10s(a very low street gear), 7000 is about 51.5 mph, in 2.66 low gear. The shift into second drops the Rs to 5026 , and then you pull to 65@6340, and you are done.
Now, in first gear, that engine will be smoking the tires all the way, so the engine is not even working hard. Then, on the shift, there is a more than a good chance the tires will continue to spin, so again the engine is hardly working.
So lets say that engine puts out a lotta hp the dyno. That is working pretty hard, about as hard as it ever will.
Now on the street, that engine has a preponderance of power,and is never working very hard, so maybe it can breath just fine thru a 750. How will you know if it is too small? I know!; time it from zero to 60. Well since this is gonna be about 5 seconds, what if a 650 hits 5.04 seconds, and a 750 hits 5.02 seconds, and an 850 hits 5.01 seconds, and a 950 hits 5.00. You can hardly measure the difference. And Do you really care? I mean it's spinning all the way already! What's the difference if you ANNIHILATE!! the tires, or just annihilate the tires?

The problem with a big carb on the street is that the primary side is really big too. And sometimes metering at low rpm can be problematic with a 4 speed. But you have that kindof covered with the "very low rear gears".

But here's what I am thinking;
If you can't idle below 1000 rpm, and you have a 2.66 low in the tranny, and say 4.10s in the back, and say 28 inch tires, then your minimum roadspeed will be about 7.6 mph. Are you good with that? Well your 1050 might not be. And your 950 might not be, you might have to go down to a 750 before you can meter that low speed. The bigger the carb, the touchier will be the gas pedal. It starts to feel like an on-off switch;when it's not doing the rocking-horse dance that is.......
I've never had a combo like yours, so I can't vote, nor recommend, but I can advise for street; easy-does-it!
 
AJ/FormS said:
It sounds like this is a street machine.And a manual trans is a special case.

Any 4bbl will rev to 7000 on that engine, on the street.
Even with 4.10s(a very low street gear), 7000 is about 51.5 mph, in 2.66 low gear. The shift into second drops the Rs to 5026 , and then you pull to 65@6340, and you are done.
Now, in first gear, that engine will be smoking the tires all the way, so the engine is not even working hard. Then, on the shift, there is a more than a good chance the tires will continue to spin, so again the engine is hardly working.
So lets say that engine puts out a lotta hp the dyno. That is working pretty hard, about as hard as it ever will.
Now on the street, that engine has a preponderance of power,and is never working very hard, so maybe it can breath just fine thru a 750. How will you know if it is too small? I know!; time it from zero to 60. Well since this is gonna be about 5 seconds, what if a 650 hits 5.04 seconds, and a 750 hits 5.02 seconds, and an 850 hits 5.01 seconds, and a 950 hits 5.00. You can hardly measure the difference. And Do you really care? I mean it's spinning all the way already! What's the difference if you ANNIHILATE!! the tires, or just annihilate the tires?

The problem with a big carb on the street is that the primary side is really big too. And sometimes metering at low rpm can be problematic with a 4 speed. But you have that kindof covered with the "very low rear gears".

But here's what I am thinking;
If you can't idle below 1000 rpm, and you have a 2.66 low in the tranny, and say 4.10s in the back, and say 28 inch tires, then your minimum roadspeed will be about 7.6 mph. Are you good with that? Well your 1050 might not be. And your 950 might not be, you might have to go down to a 750 before you can meter that low speed. The bigger the carb, the touchier will be the gas pedal. It starts to feel like an on-off switch;when it's not doing the rocking-horse dance that is.......
I've never had a combo like yours, so I can't vote, nor recommend, but I can advise for street; easy-does-it!
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That's why I said not to chose a carb by CFM and pick it on venturi size. You can use a 1.410 Venturi with an 850 base plate (1.750 throttle bores) and easily get 950 performance with 750 bottom end.
You can get a BLP BX4 for $850.00 and that gets you billet main body, base plate, metering blocks and and all the adjustablity you could want plus a BLP tune up.

For the money, it's probably the best deal going out there.
 
I think AJ s way wrong.

Good suspension and sticky tires take care of what he blabs on and warns about spinning tires.

Oh, 4.88's are a low street gear set.....
4.10's? All day everyday!!!!!
 
Every time I see this question everyone leaves out one thing at what vacuum level (restrictiveness).

So if you use said formula it's about 911 cfm at 100% VE. So if you pick a 950 your basically picking 1.5" of vacuum. Which is fine for a street car. But leaving power on the table.

Street/strip is more like 0.8-1" vacuum and full strip which only needs to mainly operate at WOT can go a lot less.
 
Leadfoot said:
A fairly competent guy with
yellow rose said:
Or Braswell.
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a calculator should be able to figure out the cubic feet of an engine, find the revolutions per minute and decide how many cubic feet of air they need to keep the engine fed. You'd be surprised(probably not) at how many people over carburete their engines and bog off the line.
Click to expand...
Correct , Karl... I have picked picked up Holley 750 & 850 double pumpers in boxes, and worked wonderful...rekitted to stock Holley specs.... Worked wonderfully...
Handed a Q.F.T 750 double pumper, with a choke ... It just is too much fuel, out of the box... for a 360 Magnum 380/ 360 cloned mill...It NEEDS to be tuned.. Make the phone call to Holley( yes , they bought them...), for the recommendations....
If deep gear, four speed(or a 3800 plus stall). .......8082 Dominator,with a two inch 4150, to 4500 adapter.. Have your head porter, match it all together, or blend it yourself... A good combo , that worked for me... An 850, would be street strip, 950 would be pure race....

Recommend a Dominator, you are already there.....JHMO....
...
 
AED had a chassis dyno at one point. You had to pay for the dyno time but they would go get just about any carburetor off the shelf and let you try it..... Talk about a marketing plan. And it's a tough day when you see a bigger number on the dyno and a slower number at the track after spending a grand on a carb.... Just food for thought OP..... 3 pedals will make a difference so if I was you the phone calls would be getting done to a few carb shops....

JW
 
4.88s for street?
Hah, I tried that,and, IMO,it sucked.Sure 7200 got me 100kph/62mph at the top of second.
But cruising 62@3760, well,IMO that's crazy.And with street suspension and 325/50-15DRs,my little 360 didn't stop spinning at the track all the way thru the 1/8th ending at 93 mph! and that with a 750DP. My conclusion was 4.88s suck. But if you like 'em so much, I have two sets I can sell you.
So then I installed 3.55,which still spin all the way past 93 mph, but now I can cruise at 2734, over 1000 rpm lower.
4.88s allow for 7200@119mph in 4th gear.
BTW
OP said"not frequently"
4.88s are very low gears for the race track. Most guys with big power will be running 4.30s
4.10s are very low gears for the street.On the street with big power, any old gear in the 3s will do, with 3.55s being middle of the road.
>OPs BB in a 67/69 Dart will be down at under 6pounds per horsepower. Good luck making that stick on the street below the speed limit,with any tire that fits in the stock tubs. It's hard enough at 9 or 8 #/hp
 
ToMang07 said:
I'd rather over-fuel that under-fuel, mileage is NOT important to me, however I don't want to be washing the cylinders out, either.
Click to expand...

This a great misunderstanding of carb sizes.
Basically no matter what carb you run on your engine it's gonna be the same cfm in your case about 911 cfm just at a different vacuum level. You could put on 2 950 and your engine ain't gonna all a sudden use twice the air and fuel. (Wash down the cylinders) It's still gonna use 911 cfm just a lot less restrictive. Not saying it will or will not work. Just making a point more carb don't equal more fuel or even air it will just operate at a lower vacuum level (restriction)

Carbs should have 3 ratings street, street strip and full race. Say at vacuum ratings of 1.5"/1"/0.5" or something like that.
 
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