Annular vrs downleg booster
Thread Starter
Instructor
Joined: Oct 2014
Posts: 143
Likes: 24
From: Prince George BC
Annular vrs downleg booster
Thinking of changing to a annular booster carb . Have others tried this change with good or bad results ?
From what I have read so far seems to be more low end torque and better throttle response . Also in my reading they seem to work best with longer duration cams , single plane intakes and larger carbs . All is which I have now.
From what I have read so far seems to be more low end torque and better throttle response . Also in my reading they seem to work best with longer duration cams , single plane intakes and larger carbs . All is which I have now.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
It all comes down to velocity through the venturies. Smaller diameter venturies in smaller CFM carbs would have increased velocity. The physical location of the booster in the airstream above the venturi determines how well it works
The boosters physical size as in annular boosters VS the smaller down leg boosters or straight boosters determines how effective they work in a lower velocity environment.
To keep a carbureted motor from stumbling on rapid opening of the throttle blades are the squirters. Just a straight shot of raw gas. So smarter people in the past figured out that the down leg booster was much superior to the old straight leg designs. Then as Carbs, cams, and heads got bigger and bigger they needed another solution. That was the Annular booster types. The draw back on annulars is that they might drop a carbs CFM by 30. But the gains in fuel atomization out weigh the negatives.
http://garage.grumpysperformance.com...boosters.5229/
http://carbkitsource.com/carbs/tech/...buretion4.html
The boosters physical size as in annular boosters VS the smaller down leg boosters or straight boosters determines how effective they work in a lower velocity environment.
To keep a carbureted motor from stumbling on rapid opening of the throttle blades are the squirters. Just a straight shot of raw gas. So smarter people in the past figured out that the down leg booster was much superior to the old straight leg designs. Then as Carbs, cams, and heads got bigger and bigger they needed another solution. That was the Annular booster types. The draw back on annulars is that they might drop a carbs CFM by 30. But the gains in fuel atomization out weigh the negatives.
http://garage.grumpysperformance.com...boosters.5229/
http://carbkitsource.com/carbs/tech/...buretion4.html
East bound and down...
Joined: Dec 2004
Posts: 987
Likes: 3
From: Jonesboro Arkansas
I went from an BG Speed Demon to a BG Mighty Demon with annular boosters on my car. Best decision I ever made. The improved signal made it much snappier. Before I had a bog that I couldn't tune out.
Race Director
Joined: Jul 2015
Posts: 13,082
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From: SW Florida.
I thought that might apply to Corvettes. We're stuck with little flat air filters. With the hood clearance issues. So the air flow at the top of the carg could still be kind of scrambled and not really pointed Straight Downstream yet. So it might be that the downleg booster that is dropped down deeper into the carb is getting better airflow than the ones that are up on the top where it could still be swirling around and hasn't really picked a direction yet. Choke air horn on the front two barrels probably helps the front to a bit. But a lot of these performance carbs have had that whacked right off flush with the top of the carb.
Last edited by derekderek; Mar 17, 2018 at 08:15 AM.
Burning Brakes
Joined: Nov 2011
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From: Willoughby Ohio
Race Director
Joined: Mar 2016
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From: Napa Valley California
Thanks for the information.
Keep it coming.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I have a 254@.050 solid cam and tried for a year to tune the carb for a decent idle by trial and error. Tried IFR and air bleed jets, a new billet throttle plate, metering blocks,....no success. I decided to go annular, and sent the carb to Quick Fuel. Came back, bolted on the engine and had a perfect idle, instant throttle, and zero bog.
Now I know the carb pros know a lot more than I do about tuning a carb, so hats off to them. But the methodical trial and error I did, pretty much lead me to the annular booster.
If you are running a radical cam,....I say go annular.
Now I know the carb pros know a lot more than I do about tuning a carb, so hats off to them. But the methodical trial and error I did, pretty much lead me to the annular booster.
If you are running a radical cam,....I say go annular.
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Thread Starter
Instructor
Joined: Oct 2014
Posts: 143
Likes: 24
From: Prince George BC
All good info . I did read info from Grumpy Performance as well as the Hot Rod article in my research .
I would not say my cam is radical at 236@.050 but is on the longer duration side for a HR cam .
In speaking with my motor builder he will take my QFT carb on trade and if I am not 100% happy with annular carb I do not have to keep it . So new QFT 750 Q series with annular boosters is on order .
Still in the middle of winter in the great white north so it will probably be another month before any test driving . Thanks all
I would not say my cam is radical at 236@.050 but is on the longer duration side for a HR cam .
In speaking with my motor builder he will take my QFT carb on trade and if I am not 100% happy with annular carb I do not have to keep it . So new QFT 750 Q series with annular boosters is on order .
Still in the middle of winter in the great white north so it will probably be another month before any test driving . Thanks all