Holley 850 Ultra XP

[RAS]

If you run this carb I'd appreciate your comments. I run a 416 inch LS3. Car is a 2012 mustang. 3300 lbs. I'm heading to the dyno soon and want to know if this carb or the 950 would be the ticket. I only turn 6700. Hyd roller. Thanks

[rustbucket79]

We have a dyno 950 uxp that ends up on 95% of the engines we run for a reference. It’s typically a few numbers better but not always. I would be surprised if the 950 was much if any better than your 850.

[mt-engines]

80496-1 out of the box 950hp

[ChopperScott]

My 434 sbc just ran on the dyno last month. We tuned three different carbs with multiple spacers. A custom built 1000 cfm, a Quick Fuel Q-950, and a Holley Ultra XP 850. In the end, the 850 made the most power. Max rpm on the dyno was 6500rpm.

[RAS]

Thank you everyone for your inputs. It's very much appreciated. My first thought was to ask my dyno operator what he thought but...a pull on the dyno is NOT a 1/4 mile run by a long shot. From what I gather, the 950 might have a better signal. What I don't want to do is spend 2 days on the dyno or 40 laps trying to dial in a carb. Way before that point I'll slap an EFI unit on it.
I drive to the track, run NA, with a manual TREMEC trans on street drag radials. Not a common build but tons of fun. I've done the other stuff.

[steve cowan]

Thank you everyone for your inputs. It's very much appreciated. My first thought was to ask my dyno operator what he thought but...a pull on the dyno is NOT a 1/4 mile run by a long shot. From what I gather, the 950 might have a better signal. What I don't want to do is spend 2 days on the dyno or 40 laps trying to dial in a carb. Way before that point I'll slap an EFI unit on it.
I drive to the track, run NA, with a manual TREMEC trans on street drag radials. Not a common build but tons of fun. I've done the other stuff.

I purchased a 950XP main body,
It has a huge casting lip in the venturi, I don't know if it would effect anything but it's there

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[6.50camaro]

Steve, I'm betting that that miss match is from the 750 1-3/8 venturi top mold used with the 850 bottom mold to taper out to the 1-3/4 throttle bores instead of the 1-11/16 750 throttle bores. Just my .02$ at a quick glance. Dan

[Alaskaracer]

That "casting lip" is not a mistake or casting issue, it's there by design....

[steve cowan]

That "casting lip" is not a mistake or casting issue, it's there by design....

booster signal ??

[1980RS]

If you take out the casting lip and the numbers get worse you will know what it did.

[steve cowan]

If you take out the casting lip and the numbers get worse you will know what it did.

I have been told by a couple of carb guys that lip is no good?
If it there by design why??
Does it help stop the reversion pulse messing up the flow cone out of booster?
Does it help atomise fuel and air with some sort of turbulence around the lip ?
Again I have more questions than reasonable answers

[ChopperScott]

Go watch Engine Masters. David Freiburger's favorite carb is the Holley 850 Ultra XP. It is used in many episodes, on many different combos. Early episodes actually feature the Ultra HP, that he refers to as XP's. The Ultra HP is the early release, same carb, before they re-branded them as XP's.

[NXBOY]

I bought a 850 Ultra main body and like so many times before removed the lip without thinking about this carb having such a big Venturi and possibly needing a bigger radius. Was 1.56 , now is 1.58.Hope I didnt mess up, I guess I can see if buddy can flow it, he has the carb plate for his flow bench. I know its dry flow but would I be able to find out much without the before Mod. flow test? I think its like 8 percent less wet flow or around. I got other 850s to compare flow too. I am using it on a stroker Bigblock at around 6000 rpm leave if needed, so part throttle is not a concern. I Can spray Dyken above it if that would show anything, wouldn't know whats good to look for. Any suggestions appreciated, i hate carb problems with fresh motor.

[jmarkaudio]

Wish I had seen this sooner. The Ultra XP 950 with a 1.600 Venturi is not a carb you want to buy. It flows and signals poorly, I believe because of the poor entrance shape. A QF 950 with only a 1.45 Venturi will flow the same air and signal much better. I have flow bench tested 3 separate Ultra 950 bodies all with the same results. For castings ATM, Proform, or Quick Fuel is best, the billet bodies I've tested from APD, BLP, and one other are all fine as well.

[learner1]

Rather than ruining carb bodies does anyone know of someone making adapter plates to bolt on the carb body so i can attach hoses to the boosters?