How to select the right carb boosters?

[travis]

Are there any rules for picking the right style carb booster? Does one style work better in certain applications than the others?

[BOOT]

I'll let others with more carb knowledge answer. Still in my opinion with modern pump fuel being designed for high pressure injection & low evap emissions, I like annular boosters. In my resent video I showed several mainbodies but didn't show that all but the stock 750 were converted(not by me) to annular, also not the 650 but there is a mini annular I'd like to try someday.


Video I mentioned https://youtu.be/iyLQCWCN1NI

[panic]

Venturi smaller than best choice: dog leg (less responsive, but does not obstruct venturi as much)
Venturi larger than best choice: annular (better tip-in, but reduces CFM slightly)

[Walter R. Malik]

Are there any rules for picking the right style carb booster? Does one style work better in certain applications than the others?

Whichever one will get you the best fuel delivery curve for THAT particular carburetor venturi / throttle bore.

They are all better in certain places within their own best environment

[Mike Laws]

Are there any rules for picking the right style carb booster? Does one style work better in certain applications than the others?

Good general answers on here. As with most things - it depends on application.

[n2omike]

If the engine's demands can easily be met with a 4150 style carb (up to around 550-600 hp) then you can either use an efficient venturi shape along with a downleg booster... or a larger venturi with an annular booster. Both can give good results. If you need more airflow than that, you either end up with downleg boosters in less efficiently shaped large venturis in a 4150... or move up to a Dominator. Both trade off lower speed efficiency for the extra airflow.

There hasn't been a 'Goldilocks' carb built for engines making 600-800 hp. It's beyond the 'sweet spot' of the 4150 style, and the Dominator was never designed to be all that friendly except for racing at wide open throttle.

There are probably some expert carb builders that can make the existing carbs fill in the blanks, but even they would likely enjoy seeing something in between the 4150 and Dominator. That seems to be one place where EFI is finding a happy place... as they do not have a booster in the way of the airflow path, so they can flow more than enough air through a 4150 flange to make great horsepower, while still metering well at lower rpm.

This being said, I am not a carb builder. Just my observations and $0.02... for whatever that is worth. lol

[BradH]

...

There hasn't been a 'Goldilocks' carb built for engines making 600-800 hp. It's beyond the 'sweet spot' of the 4150 style, and the Dominator was never designed to be all that friendly except for racing at wide open throttle.
...

Might be the right niche for one of Mike Laws' Twin Blade sizes, if a nicely set-up 4150 still misses the mark for whatever reason.

I don't know how the commonly available EFI conversions for NA applications in the 700 +/- HP range respond to cams with lots of overlap and higher/rough(er) idle speed. I know folks on this board & elsewhere who have suggested that I switch to EFI, but this is one of the key concerns I'd have with doing so.

[F-BIRD'88]

This is an example where a 6 venturi carb would fill the gap on a racey single 4 bbl manifold (with an adapter)
50% more flow. eg 1125 cfm from 750 hp size venturii.
6 instead of 4 venturi

[1980RS]

My converted 2 circuit 750 Dominator to a 1050 2 circuit works like a charm on the street and run great, it's just a giant 850 IMO.

[Walter R. Malik]

If the engine's demands can easily be met with a 4150 style carb (up to around 550-600 hp) then you can either use an efficient venturi shape along with a downleg booster... or a larger venturi with an annular booster. Both can give good results. If you need more airflow than that, you either end up with downleg boosters in less efficiently shaped large venturis in a 4150... or move up to a Dominator. Both trade off lower speed efficiency for the extra airflow.

There hasn't been a 'Goldilocks' carb built for engines making 600-800 hp. It's beyond the 'sweet spot' of the 4150 style, and the Dominator was never designed to be all that friendly except for racing at wide open throttle.

There are probably some expert carb builders that can make the existing carbs fill in the blanks, but even they would likely enjoy seeing something in between the 4150 and Dominator. That seems to be one place where EFI is finding a happy place... as they do not have a booster in the way of the airflow path, so they can flow more than enough air through a 4150 flange to make great horsepower, while still metering well at lower rpm.

This being said, I am not a carb builder. Just my observations and $0.02... for whatever that is worth. lol

Braswell has a B-4825 which is exactly that but, it is expensive.

The Get'm Garage "Twin Blade" somewhat works in that realm, too.

[Tuner]

Venturi smaller than best choice: dog leg (less responsive, but does not obstruct venturi as much)
Venturi larger than best choice: annular (better tip-in, but reduces CFM slightly)

Straight leg booster restricts venturi less than down leg.

[GARY C]

Does anyone have info on the NASCAR 4150 830 cfm carb that was supporting 870+ HP?

[BradH]

Does anyone have info on the NASCAR 4150 830 cfm carb that was supporting 870+ HP?

If I have my facts straight, they were basically "control carbs" in that they were limited to 1.59" venturi and 1-11/16" throttle plates. Not exactly an ideal venturi-to-throttle ratio, but everybody had to work w/ the same basic config.

I've seen them being eBarf'd regularly since NASCRAP went to FI. Looks like they were run with both 2-circuit and 3-circuit configs, as well as various down-leg, annular and the occasional straight-leg booster.

The Braswell 1.59" v 2-circuit main body that I used to build this carb came with some oddball straight-leg boosters that I'd never seen before... kind of a cross between an annular banjo and a large-hole down-leg. It was a former Robert Yates Racing carb, FWIW. I punched 'em out and put in annulars as part of retro-fitting it as a 1.59" v x 1.75" throttle config.

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[jmarkaudio]

I use annular for most new builds, but also size the carb accordingly. Small carbs and engines with a lot of heat may not need an annular.

[BOOT]

I use annular for most new builds, but also size the carb accordingly. Small carbs and engines with a lot of heat may not need an annular.

Another excellent point, I set my cars up to run cool and that's why I decided to get my first mainbody converted to annular. Still like many things(ie spacers) sometimes you just gotta try each and see what works for your app.