I just put together a low deck 512 for a 68 roadrunner. It has Indy S/R heads with max wedge openings (still has a pretty good pushrod pinch though) Solid roller .648 lift and 262 at .05 on a 108 l/c , 10.8 compression. I have the Indy single plane intake with a 4150 flange. Right now I have two carbs, one is a brand new 3 circuit Quickfuel 1050 dominator, and the other is a really old 950 hp Holly. I'm not sure if I should try to run the dominator, the holley, or something else. Oh, the car is a street strip deal not a full time race car. torquflite, 9 1/2" ptc converter and 3:91 gears.

Labrat and myself did so testing on his car(440) and
he had a 850 on it and it would launch great with the
850 but with the 1050 it would make more torque and
spin the tires... if I recall right it had better
mph with the 1050 but with spinning and the 850 had
a better ET due to traction

Ok, thank you Mr.P Body . I would think with my motor the big carb would be the way to go. Kind of wondering if a 1050 in a 4150 style would work better. Not sure I can tune the dominator. I have a wide band I'm going to use no matter what i bolt on the manifold. Also, I will have to rig something up to hook up the kickdown linkage to the dominator.

I have a QF 1050 setting on top of an Indy single plain with max wedge ports on my 511. I’m not happy with it. I'm thinking of going to an 850 with an Indy duel plain intake for better drivability since the car this engine is in is primarily street driven, has a GV over drive in it and rarely sees much over 3,000 rpm. The other option I am looking at is to go with EFI. It depends on how the car is being used which carb is best.

So dabeast2, what is it you don't like about the 1050 ? is that a 4500 or a 4150 ? I would have prefered the indy dual plane on my motor as well, but they do not make it for the low deck. I think Streetwize had the Indy dual plane on his 512 and it worked really well if I remeber correctly. That's a big problem with the low deck, there's not much of an intake manifold selection. Even something like a super victor would probably work better, but alas, it is not available to us low deck guys.
Fuel injection would be ok too, but is kind of expensive. I'm not that up on it to try a megasquirt deal.

I would not run a dual plane on an engine that big, ever. Efi will not like it either..

Back to the carb question. We run a pump gas 512 RB motor with EZ1 unported heads and the Indy intake with a 4150 in a 950cfm Proform carb, and I have to say with over 132mph in the quarter, it kicks butt. I like the 950 on a milder motor over the bigger carbs so far. Easier to jet and tune. We would gain a little on the top, but I am not sure that the bottom would improve at all, if any, but we didn't have a really nice new QF dominator, ours is a much older one.

The cam and convertor are what need to pull the signal on the carb for it to work when the timing is set. If you have an overly tight converter for what you are doing, or a rather tall gear, then an annular booster carb might be more in line for a more sensative transition. They are more responsive than down leg boosters, and work well on the street. A race engine doesn't function for but a fraction of a second during the transition, where you engine may live in that zone. A 4150 in either a 950 or 1050 would be the best choice, and maybe with annular boosters. I would call one of the carb shops and get it straight from them to be sure. Is you QF1050 an annular booster carb? If it is, there is a good chance, that will runn really awesome.

Ok, I don't know where this all leaves me.LOL.... The QF 1050 domi i have is annular booster, and with those and the reasonable venturi in the 4500 style it might have a decent signal. On the other hand, going a buck thirty two with a QF 950 tells me it is more than enough carb for my motor. I should probably look into that. An SV1 might be a good option too. I'm kind of confused on all of this, it seems a lot of things will work. It's just a question of what will work best for my application.

I have a pump gas low deck 518 (4.375borex4.300 stroke)in my Duster, 3450 Lbs. with Indy SR M.W ports on my car. I have treid both the 400-2 and 400-3 intakes, I have tried both on the car with a Holley 850 D.P.,it is a 4781-6 non HP , and a 1.5 inch phenolic spacer. I have used the 400-3 a with a cloverleaf 1.5 inch phenolic spacer and several different Holley 1050 Dominators, 9375 with standard boosters, 9375 custom with annular boosters and a 9375-2 HP with standard boosters. Don't confuse the standard dominator boosters for annular boosters in them , there is a big difference My car runs faster at the track with the bigger carbs, I do have a dual wide ban and I'm working on cleaning up the mixture on the idle and trasnition circuits on all of the carbs, that makes a heck of a difference in the way they drive on the street Put the big one on it and work on the mixture at slow speed, don't change the primary jets for that, modify the idle and transition circuits to make it right BTW, is your big carb. a two circuit or three circuit carb? My Holley 9375 are two and the 9375-2 HP are three circuits, I had to open the primary side intermediate bleeds to .073 from .063 to get rid of a bad starting line bog on the HP carbs EFI would be neat but it is not in the cards for me now, maybe later when better changes start to occur next year

I don't know, the Dominator booster sure looks like an annular to me, but I'm no expert on those things. My QF is a 3 circuit, which has me a little concerned. I know they can run very rich on a street motor. Maybe it would be a good idea to send the QF dominator to one of the carb shops and at least get me in the ball park. i can tweak it from there with my wideband. Hey Cab, which manifold did you like better with the 4500's ? the -2 or the -3 ?

I have Indy EZ heads on the 493 in my 63 and I do use the Indy dual plane intake. I am using a basic 850 DP as thats the carb I had and could not afford another at that time so I used what I had. But I will say the street drieabilty is great. It really runs nice with it. I guess it would be faster with more carb but I am happy at how well this 850 works. It is a 10.6 comp pump gas eng that I race thru the pipes like I dive it. At 3700 lbs it has run 10.70's so far driving it to the track. It is a flat tappet solid cam. Ron

I have a Pro systems 1000HP what was calibrated for a 720 HP motor on my 517 Low Deck that has a tad more compression and slightly better flowing heads but a little less cam 264/268 @.050 Bullet Hydraulic Roller. It's Killer, response is like a super comp motor.

I can get you the build number if you want.

You have two of the most popular carbs you can possibly buy...
I cant think of any reason not to try them both and see how they work... Its been proven those fancy $1K carbs run and make absolutely zero more power than the stock HP base carb tuned.
Rebuild kits are just pennies compared to a new carb

I also agree with Bob, I'd try t ogo as far as you can with the ones you have first.

I have 2 pro systems 1000HP's and I'm very happy with them. For a dual purpose car the calibration of the 3 circuit Dominator metering blocks has been spot on. For a true race only car you're primarily concerning yourself with the WOT tuning for max power and the shot. On a true street driven car the roll-on loading/transitional circuit is more critical to get just right, even though in a side by side dyno run 2 carbs properly jetted for max A.F power may not look like much of a difference, in real world driving that intermediate circuit tune can make a huge overall difference. Patrick seems to have a very good hand-hold on these big inch motors for street-strip use.

My 950 is an old one, i think it has the 1 3/8" venturis.I do not remember if it had the screw in air bleeds. That carb just seems kind of small for a 512. i would think I'm leaving a lot on the table if i use that one. The QF dominator might be really good if i can get it dialed in. It might be worth it if i can send it off to Pro systems or someone like that to get it close. I'm still kind of interested in an SV1,and a good 1000 hp 4150 might be perfect. I still don't know. LOL