JMHO but if you're getting a good deal on the Demon I don't think you'll regret it. I'm running a 1050cfm Race Demon on a stroker Clevor and I dig it. It's very tuneable.

Steve

I recommend

1. Double pumper
2. Down leg boosters
3. 850-950 cfm

I'd run a 950 HP as a minimum, but would advise you go with a 1000 HP Holley or an 850 Barry grant or 850 QFT

The 950 is a misnomer, its a 750 with an 850 baseplate and isnt a very big carb for what you have.

I run an almost identical 489 FE in my 3500 lb Mustang, with an almost identical running gear and run an 1000 HP series carb, it is very streetable and very much not fussy.

The 1000 is actually dimensionally the same as an 850 asides from a shaped entry area, and remember an 850 isnt out of place on a heavy 454 or 460 with an automatic in a full size car or truck. I promise you have enough motor to happily use a good 850-1000

The 950 is a good carb, but it is smaller and will lose top end charge, but gain you nothing down low over a modern 850 or 1000 HP.

Keith recommended the Quick Fuel 780 vacuum secondaries for my Pond 482. More ponies can be gotten with a bigger carb at the expense of throttle response and smile per gallon. :MECOOL:
Dyno sheet is in my gallery.

I have a 482 Pond from Keith with a ported Blue Thunder intake and ported edlebrock heads. I started with a 850 Mighty Demon (carb sucked:mad:). Went to an 830 Holley. Still rich for driving conditions and street use. Then I got a Bigs 750HP. Much better. Most people do not consider driving style and what you are going to be using the car for. If your plan is to drag race the cobra then go with a 950 DP. If you plan to go open track the Cobra then get a blue printed 750 HP.

Go with KCR's recomenditions
 

767Jockey Since KCR is selling the heads and camshaft to you, It would be a little foolish to not go with his carb choice. I don't know what manifold you are running but I would send it out to Joe Craine and let him balance the ports up. On some manifolds there is a 10-30CFM differents between ports. I would also give him the size of the ports. You want the intake ports to be just a hair smaller than the head ports. This gives a smooth transition. Rick L. There is a formula that works pretty good for getting the right carb size. I would being looking at something in a 650- 780 for the street. The dyno work with the A/F readings are going to tell you what the motor wants. Carbs are like camshafts, bigger is not always better,%/ It's just BIGGER.;):cool: Rick L.

YEP, of course I agree Rick. After Bigs worked over the 750HP they said its more like a 780cfm.

I personally think that going too small on a dual plane is giving up a ton of mid and upper end without gaining anything down low. In the very least try both, dont just go small, you have a serious motor

A single plane with a large plenum may be a different story, easy to overcarb and they can be a bit fussier down low, but a dual plane needs as much airflow as it can get, any one cylinder is pulling from a plenum fed by only 1/2 of the carb, and airflow at the booster is not an issue with 480+ cid and the RPM port and plenum size.

I run a 1000HP on my 489, I run a/c when its hot out and in 5th its an overall 2.36:1 final drive. I run it around town like a stocker, or will spin it up and let it roar with no downside.

I had a 770 on it for a while diagnosing an issue that turned out to be ignition-related, and it was like I was pulling a parachute with no gain in low end drivability or mileage at all. I didnt dyno, but if you told me I lost 50 hp I'd believe it, heck maybe more, it was amazing. I am not stretching the truth at all. A white knuckle ride, repeated before and after the 770 was noticeably tired above 4500 with the small carb, and both were tuned as well as I could dial them in.

Remember, hot 427's in the day ran at least 2 600's if not 715's, and you are adding 55 cubes and much more efficient airflow! How can a 780, perfect for a mild CJ motor be good for a light car and a 482?

Vizard's old rule of thumb is 2 cfm per cid, recently he has published some other discussions of carburetor sizing on a dual plane that blows away the small size belief, even on small blocks

Try a 780 if you are concerned, but for laughs, beg or borrow an 850, or even better a 1000 from HP or Quick Fuel, and do a back to back street run or even better dyno tests, you'll see. That motor needs air, more stroke, more bore, much advanced heads and intake design, why choke it?

Recently ran a pump gas 445 inch 390 based stroker on the dyno. Mild Edelbrock heads and a BT dual plane. Pulls from 2500-6500RPM. Went from a 750 double pumper to an 850 double pumper with no other changes - back to back withing 15 minutes. Engine picked up 35 horsepower at peak (to 485HP) and lost nothing anywhere.

Go big....

Barry,
Hmmm...I might be selling a nice "Dyno time only" QuickFuel 780 w/ vacuum secondaries in the near future. :p

Quick-Fuel 950 on mine

Keith tried a 750 then an 850 and said he wasn't getting what he wanted from the motor on the dyno. He upgraded me to a QFT 950 and it's great.

Dan

All,
Keith and I both have crazy schedules and it's very hard to actually get a mutual time to speak on the phone. We finally got a chance to speak today. He strongly recommends a Quick Fuel 950 - that's what I'll go with. Thanks for all the input, very interesting and informative comments, I really appreciate all the input. Thanks.

Barry-
This is interesting. At what rpm did the engine pick up 35 hp? If peak hp was in the higher rpm range where you never really drive on the street (6000 rpm plus), the argument could be made that you are better off with the smaller carb- I noticed that you don't say that the bigger carb picked up anything over the smaller carb other than at peak hp. And although you state that the bigger carb did not loose anything relative to the smaller carb anywhere, that is with the engine on a dyno, do you think that once installed in the car and were out on the road, the smaller carb would have better throttle response than the bigger carb? So I guess that is a long winded way of asking, notwitstanding that you may pick up 35 hp, might you still be better off with the smaller carb for non-race/street driving?

I am at home right now and do not have the dyno sheets with me - although I usually keep copies at the shop.

In general - if I recall correctly - there was not a single point through the entire pull where the smaller carb had any advantage at all. The gains were fairly linear, with a smaller gain at lower RPM getting smoothly greater as the RPM went up to peak. Peak on this engine was only 6200RPM. In other words (I'm gonna kinda "make this part up" since the sheet ain't in front of me) the motor gained something like 20 @ 4000, 25 HP @ 5000, 30 @ 5500, 35 @ 6200....

Obviously I have no way to quantify the in-car characteristics of the two carbs. Although we threw a few jets & such at each one I am certain that neither was fully optimized - but they were in a very comparable state of tune. Based on this data, I would not personally choose the smaller carb unless it were going into something heavy or with highway gears - like a Galaxie or a truck.

Thanks, that's interesting. Could you post the dyno sheets if you can find them- I'd be intersted to see them. What were the specs of the cam that you had in that motor?

KC Shelby 482 - 950 Holley (DiVinci).
Once I supplied and regulated the fuel properly, (5psi), it runs awesome. response is RIGHT NOW. No flat spots, and idles at 850.

I looked it up, and you're right, the 950HP carb has similar venturi diameter of standard 750, but throttle plates of an 850. As the 950HP carb has a recountoured/reshaped top entry for better flow compared to a standard 750, I'd think it would therefore flow more, but bby how much I don;t know. Obviously, Holley thinks that the carb should be rated at 950. Does removing the choke tower/reshaping the entry zone improve airflow that much? How much restriction is in the venturi diameter or base plate throttle bores/plates?

Interesting.

I wouldnt lie to ya ;)

With that in mind, the 950 is a hell of a carb for the smaller motors, a bit more flow than a 750, but good airflow across the boosters with the smaller venturi size. I can almost promise it doesnt flow 950 though LOL

I also would say a 1000 HP doesnt flow as much as an equiv Dominator, its sorta advertising math :)

However when you start talking a deep breathing 450+ cid engine, a 750-780 just isnt enough, the 950 may be if you never really work the motor to its potential, (to include WOT mid-range) but if thats the case, why pay for stage "whatever" heads, the setup will outflow the carb at ease with a good cam and good exhaust, add good heads and the carb now is your restriction.

I consider the 950 a big-cube or high revving small block carb, and a good one certainly, but like I said, sometimes a little old school thought is appropriate

A stock stroke Mopar, Ford or Chevy at 440. 429 or 454, you name it, with a reasonable set of gears in a Charger, Galaxie, Impala, etc would be happy with an 850 in any of our "younger day cars" and no-one would question it

Now add more airflow with some good heads, a more modern cam, 40+ more cubes, and a modern intake in a lightweight car. It needs air and will happily use it, how can you logically go backwards?

I understand the old "dont overcarb" idea that we read in the rags, but this isnt a 350 Chevy or 302 Ford :JEKYLHYDE

The motor is too big for Webers (48s are too small), unless you can get the rare 58s. Keith put a single Pro-Systems on my 482 motor and it has been great. Not sure what size it is, but the motor puts out about 630 hp and tq and is easy to drive (just not great under 2200 rpms).

I run a Holley 850cfm on my top oiler for the last 10 years...never had a problem with it. I'd also suggest a Street Demon 850cfm...I ran one of those on another car I had and it ran great.

Ron