A lot of 750 carbs are close for a 350 Chevy out of the box. Those guys slap those on without question. Mopar guys put small port heads on 500” engines and worry they will have poor driveability with an 850. See this a lot. This one has the 270s so bigger would be better without question.

Don't forget that the right foot determines how much air and fuel goes into the motor at anything less than WOT, no matter what size the carb. is

I have the QF 1050 AN on my 493 Indy head Savoy and it runs pretty strong but I'm sure it would have better street manners with that 850 XP deal.

Gus

I've made really good power on the dyno with the QF 1050 AN. It is a great carb for making top end power. I've never tried to drive on the street with one though.

I ran a 1050AN on the street with my 512. I built the carb. They need a little bit of transfer slot restriction for street use but mine was absolutely a great carb. Could easily daily drive it, get decent mileage, and run high 10’s.

I ran a HP1000 (850) on my 505 with Source CNC heads , daily driver / strip . Ran great , 10.50 best dragging the brake . Great driving on the street . Went to a 1050 4500 only a small gain but more consistant - till I fitted TF270s . Then a lot faster / quicker .
I ran that HP1000 on both my 440 and the 505 .

Tex

...I remember the commit that was said about the Crysler 440+6 that were rated something like 1300cfm.when i was researching the carb for my engine Holley had the nice little crab recommended deal (can't remember the name of it) on their site where it depends on the use of the car, they would recommend a cfm for you....it came handy for me.

i would like to try a pair of big [850 ?] thermo-quads on a 440 some time.
i really like those carbs after figuring them out, and collecting [actually making] a bunch of jets and metering rods.

What do you do about the differences in the front versus the rear throttle bore size and CFM differences feeding the cylinders at WOT?

I dunno about that... one of the complaints w/ the 850/950 XPs is they may do OK on the dyno, but drivability isn't good because their tunes aren't "street friendly".

Had a 505 on the dyno yesterday....... pretty similar build to what the OP has outlined,
The one here would be a tad milder.

We used a Brawler 1050 downleg on it-
https://www.holley.com/products/fuel_systems/carburetors/street_strip/parts/BR-67209
After a few rounds of jet reduction, it ended up in the high-12’s/low-13’s at WOT, and 13.7’s or so at 3000rpm(50-70 hp)part throttle cruise, with 82/90 jets.
That motor only used 820cfm@6300.

That carb seemed to be a pretty good match for that build.

if on a single plane intake or a tunnel ram, that may take some "popcicle stick" thinking to even out the fuel distribution.
on a dual plane intake [if there is such a thing for an RB], i would imagine there would have to be some fiddling as well but not as much as a single plane intake.
to be clear, i have thought about this for years, but i haven't done anything about it.
also, don't forget the adapters needed to bolt on the T-Quads, as i don't think there are any dual quad intakes out there that are set up for spread bore carbs. those will more than likely need work as well.
i think there was a member here, ["Quick D-100" perhaps ?] that tried a pair of T-Quads on a tunnel ram, and i think he said they worked pretty well.
so who knows ?
just something floating around in the cobwebs of my noggin...........

Yeah, 600 hp uses 850 cfm and 700 hp uses 1000 cfm. This assumes a BSFC of 0.50 which is the typical performance engine assumption. A well designed race engine needs less fuel and air to make the same power.

2bbl carbs have a different rating system. 440+6 rating in 4 bbl terms is around 900 cfm not 1350. The 1350 sounds cool but it isn't the same as a 1350 four barrel carb. Lots of people have been confused about this since forever.

Which intake is that?

Great info! Thanks for providing!

I'm so jealous of people that don't need a choke on their build, really limits the carb choice.

Edelbrock made two different versions of their in line dual 4 barrel 440 low rise manifolds, the later one was a dual plane and it worked a lot better than the first version which almost a single plane intake
My point is on using a set of the completion series 850 CFM Thermoquad on one o fthose low rise dual 4 intakes they would have a really bad fuel distribution at WOT on the #3 and 4 cylinders as well as the #7 and 8 cylinders at WOT due to the larger secondaries
I used to know a Ford street racer guy (in SO CA a long time ago) that tried two Carter Competion Thermoquads on a 1971 Mustang Boss 351 Cleveland motor on a tunnel ram, it ran oaky, but it wasn't as fast as my stock gutted for street racing 1970 Duster 340 with a LD340 Intake and Holley 650 D.P. carb 4 speed car Never underestimate any Mopar car

thanks Cab. now i understand.
i wasn't thinking about the cylinder position in relation to the physical location of the larger secondaries.
i was thinking in terms of how i like how those carbs work in a single carb application, especially on a dual plane intake, where the secondaries can be seen by all cylinders.