Dogleg or annular boosters?

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richyrich
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Dogleg or annular boosters?

Postby richyrich » Sun Aug 31, 2008 5:01 pm

Im building a 421 sbc 650+ HP 13.0:1 compression 80% race 20% street engine. Im looking at the pro systems carbs pro series 4150 carbs and just wondering if I shoud go with the dogleg boosters or the annular boosters? also not too sure what cfm I should go with either. I was thinking around the 950 range?

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Annular vs. Downleg

Postby GOSFAST » Sun Aug 31, 2008 8:05 pm

Recommend the "annular" over the "dogleg's".

Personally, would also have used 14:1 (minimum) as a starting point for C.R. We like closer to 15:1 in "fuel" builds.

Recently delivered a "pump-gas" (93 octane/11:1) 406" SB, 615+ HP, 1050 Holley (annular), fairly small solid-roller, RHS235's (minimal porting), 2.000" primaries.

There was no HP "chasing" here, bolt the parts together and go racing!

Runs a '72 Camino (3600#) to a some 10.70's at 124.

Thanks, Gary in N.Y.

P.S. Thanks to Frank Lupo at Dynamic Convertors! One "super" convertor in this ride!

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Postby jmarkaudio » Sun Aug 31, 2008 11:03 pm

I would get as big as you can get in a 4150, and ask Patrick if you plan to buy a Pro Systems carb which boosters. If you go with his recommendation and if you have issues it is his to fix, not yours.
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Postby Dodge Freak » Sun Aug 31, 2008 11:29 pm

My Demon "race" carb can change boosters...all their racing line is like that...believe the king demons too. So you can unscrew the boosters and swap them and test and see.

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Postby RayJE Carburetors » Tue Sep 02, 2008 3:35 am

annular boosters in a 4150 body kill the flow of the carb... even with a 1.57 venturi the 900 thou outside and 550 inside diameter annular booster kills flow..... for 650+ HP out of a 421 ci small block a 1000HP body with downlegs will make the most power.

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Postby 3V Performance » Tue Sep 02, 2008 6:49 am

RayJE Carburetors wrote:annular boosters in a 4150 body kill the flow of the carb... even with a 1.57 venturi the 900 thou outside and 550 inside diameter annular booster kills flow..... for 650+ HP out of a 421 ci small block a 1000HP body with downlegs will make the most power.



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Postby blow-thru » Tue Sep 02, 2008 7:39 am

If this is the case annulars killing flow what is the benefits to them is it only signal strength or are there other advantages ???
Please enlighten us all on the annular design ....
Cheers Carl...

ps by what amount do they kill flow ?????

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Postby richyrich » Tue Sep 02, 2008 8:06 am

I was wondering the same thing. From what I have read in almost all magazines and websites, the annular boosters always come out on top. But most racers still prefer the downleg design right? Is it true the the annular booster only helps with the fuel atomization and simply kills the flow?

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Postby 3V Performance » Tue Sep 02, 2008 8:30 am

richyrich wrote:I was wondering the same thing. From what I have read in almost all magazines and websites, the annular boosters always come out on top. But most racers still prefer the downleg design right? Is it true the the annular booster only helps with the fuel atomization and simply kills the flow?


From what we have seen it hurts power by about 6 to 8hp on a 850 to 900hp engine.

Engine size and rpm will change this.


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Postby richyrich » Tue Sep 02, 2008 11:46 am

So simply put engines that thrive on huge air and fuel flow such as race engine or high HP engines are bogged down with the restrictions of the annular booster? The only engine that can really benefit from the annular booster are street engine with under 800hp carbs?

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Postby panic » Tue Sep 02, 2008 6:23 pm

Another swing and a miss.
Last edited by panic on Wed Sep 03, 2008 8:09 am, edited 1 time in total.

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Postby MadBill » Tue Sep 02, 2008 6:42 pm

I had a pair of 850 CFM Holleys converted to annular boosters and choke horns removed for my Rip Van Winkle 495 BBC project and did my own throttle shaft slabbing and airfoiling of the blades. They flow 965 CFM dry and one or the other has out-powered all comers (3 pro-built and another 4 off the shelf 830 to 950 CFM non-annular units) on two chassis dyno and 3 engine dyno tests on SBCs in the 540 to 670 HP range...
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annular boosters

Postby bigjoe1 » Tue Sep 02, 2008 8:09 pm

The main feature of the annular boosters is it will work over a very broad RPM range( especially down at very low RPM) where the normal boosters will not function correctly at very low speeds9 Once the RPM is up pretty high( 6000-7000) the boosters no longer have an advantage, and they might actually hurt top end performance. On race carts, if the converter is way too tight, the annular boosters can makr a reral big differance in performance.

JOE SHERMAN RACING

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Postby MadBill » Tue Sep 02, 2008 8:23 pm

joe X2!
Another way to state this is: "You can use a bigger carb(s) for more top end power without killing the low RPM response."
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Postby MaxFlow » Tue Sep 02, 2008 10:21 pm

X3.............bigger carb on small motor with annular for sure. At least in my experiences.
Joe Stalnaker
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