850XP Holley good for 508" RB?

I'm getting close to having all my parts after 6 months of ordering and waiting for parts to arrive. Most people tell me I'll need a 950 or bigger. But on these forums I see some saying they are using an 850 with good results with a similar size engine.

Quick summary of my build. 440 block, .040 over. ~10.5 to1 compression expected. 4.25 stroke, 6.8 rods. Trickflow trackheat intake ported. Trickflow 270 heads. Jones or Bullet hydraulic roller cam. (Got one from each, long story.) Cam will likely be 253/260 @.050", .390"/.390" Lobe Lift, .624"/.624" Valve Lift, 114 LSA. TTi 2 1/8th step headers. MSD billet distributor w/6AL. Car is a 1969 GTX, ~4000lbs. Dana 60 4.10 and hemi 4-speed.


Thoughts on this carb meeting the need?

you need to look at venturi size on the carbs, as some of the old 850's are actually a larger venturi than the 950 carbs.
for example, are you talk about an 850 carb with a 1.53" venturi vs. a 950 carb with a 1.45" venturi?

Here's the carb; https://www.summitracing.com/parts/hly-0-80804hbx

QF 4150 1050AN

Exactly!!!

The 1050/4150 is a 1.59. Other than that an old 1.53 850 would be my choice. It’ll handle a big carb. Hell I run a 1050 1.69 Venturi dominator on my 500 ci 4000# street car at times. Works well.

I think that'll be a very strong combo with great throttle response. Should be a blast to drive.....definitely going to find any weakspots in the drivetrain

You went with ported 270's...You will want the 950 or a 1050 in a 4150 carb.......850 is too small. The Proform Race series are almost perfectly calibrated to this type of combo and I highly recommend one of those or a Thumper carb if budget allows.

What use will the car see ? For mainly street, the smaller carb could likely be smoother off-idle and cruising.
If it'll see the track - for which the build seems targeted - it'll want more CFM; I'd be thinking 1050 or so.
Either way, at that weight with a stick and good hook, you're likely to find what parts of the drivetrain become consumables...

This is and will be a street/strip car. Will need good street manners as will go to car events, light to light fun, and occasional strip visits. I'd expect it to be a strong street bruiser. BTW, I also in the past have run up to a 15 shot of NOS. Will have it but likey not use it as won't be able to build another engine in this life time. :-)

That 850 should work just fine. Those XP carbs are very nice to work with. For max power you could go larger but it might not drive as nice. For street driving I'd use a really nice 750 carb but it will give up a little bit of top end power. If you are computer savvy you should consider a Holley Sniper EFI setup since it will do a lot more for you for not much more money. But if you aren't computer savvy then don't bother since it is easy to get lost in an EFI conversion.

Nice components, questionable out-of-the-box tune

My suggestion is to join this forum, then do some searches and/or ask questions on that particular carb model: http://racingfuelsystems.com/viewforum.php?f=5

What are the specs of both cams? I gotta say the 114 LSA for that combination strikes me as... odd.

Thanks for sharing that forum. I will check it out. The 114 is to help with power brakes and I've heard the wider spread can help with NOS?

Bullet cam specs are Intake

248 @.050”

.382” lobe lift, .573 with 1.5 rocker

300 duration @.006”



Exhaust

254 @.050”

.380” lobe lift, .570” with 1.5 rocker

310 duration @.006”



113 lobe separation

109 intake centerline

Seems like your not convinced....We run an old 512 with ported iron heads and 2.14/1.81 valves with a .560" lift cam and no duration.....We run a 1050 on it in the street class....It would run out of leg before 5000rpm until we switched. And get this, our nice little street car with 3.91 gears, no convertor and 512 runs 10.76 in the 1/4 at 125mph....Its an unreal little sleeper.

Q's for the OP:
Are your tracks 1/8th mile or 1/4?
How tall are your rear tires?
How much RPM are you expecting to turn?
You've driven a stick car on the bottle before?

No I'm convinced a larger carb is the way to go. Seems like based on some feedback I could get away with using the 850, but would leave a lot on the table. Looking to stick with a 4150 model to work with the ported intake. Like your list in your profile. Clear you have a lot of experience. Thank you!

1/8th mile. 28' tall, 10.5 inch Mickey Thompsons. I've just gotten into 4th in the 8th in the past. Yes, have run NOS with my stick for over 20 years.

I did a lot of carb size testing back in the early 1990s when I wanted to race in NHRA S/ST class with a stock bore and stroke 440 motor in a lightweight Duster (2800 Lbs. with driver ) with ladder bars and leaf springs on a floater kit.
I started off with Holley 650 D.P. thinking it would 60 ft. better with the smaller carb to make the reaction times better, WRONG. I ended up going to a 750 D.P. then a 850 D.P. then a 950 HP D.P. and finally ended up with changing the intake for a single List # 9375 1050 Dominator CFM non-HP carb.
My message is the more air and fuel I fed it the faster and quicker it went
I've seen the same thing on engine dyno testing on BB Mopar stroker motors and stock stroke 440 motors, I could NOT[ over carb them rascals
I would try your carb first and see if you want the car to go faster after max tuning that combination.
What are the cam specs on the other cam? 114 LSA is way too wide for most single carb non race only motors in my opinion
BTW, is this a race car, street and strip or street only car?
I used to have a dyno only motor I used for testing, it was a 440 block bored to 4.380 with a 4.375 stroke, one of the last dyno test I did on that motor was swapping the Indy 440-3 intake with a Holley 1050 CFM Dominator carb to a tunnel ram intake and two Holley 1050 CFM carbs, that combination made 30 more HP at peak RPM than the single carb set up did
BB Mopars motors like more air and fuel for WOT driving
Be careful please

OK; I was wondering how high you were gonna have to rev it, considering hydraulic rollers have the rep of not handling high RPM well.

If you're putting the emphasis on performance while spraying, then the wide LSA makes more sense. But if NA is the primary mode and nitrous is less frequent, then IMO it's too wide for best NA use.

Not an answer to your question, but a radiused exit directly below the carburetor's mounting surface will always raise CFM.
A 3/8" thick plate (matching the base flange) with sized holes matching the throttle plates, and 3/8" radius leading from each bore into the manifold improves the flow discharge coefficient.

BB Mopars motors like more air and fuel for WOT driving.




I had a 60 over 440 years ago with a set of stock Hughs stage 3 ported 906's with one of their cam shafts the cam shaft was the HEV56 I believe any long story short the engine would run on the lean side with a 750 DP. Switch to a 1050 Dom and all was good never made the car any faster i think the extra fuel cool the combustion chambers.

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.