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 Annular vs Down-leg Boosters - Holley Carb
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GtoGuy32
Cochise

USA
842 Posts

Posted - 21 Oct 2015 :  11:45:25 PM  Show Profile  Reply with Quote
Hi guys,

I am sizing up my next carb for my increased head flow and cam upgrade for my 455 HO round port engine. I currently have an AED 850 HO. I absolutely love the carb. It was almost dead stoich out of the box and was perfect after a jet change. The carb has delivered really solid throttle response and has fed the engine well up into the 6000 rpm range.

I reached out to AED to get their thoughts about carb choices. They have recommended their new Annular Booster version of the 850 HO with an HP body.

The HP body is supposed to flow 25-40 cfm over the milled choke body (plus)

The annular boosters should atomize and provide more fuel for a given air velocity through the carb (plus if tuned right).

The annular boosters may restrict the flow cross section a bit due to their size, but likely not as much as the HP body offers up (plus and minus).

I guess the 4500 (dominator) carbs use annular boosters, but don't know of other 4150 carbs using them.

Any thoughts or experience? The feedback from AED is that overall, the annular booster carb performs generally better and has a decent broad range of performance.

Thanks

-Dave

Edited by - GtoGuy32 on 21 Oct 2015 11:46:58 PM

Chicagogoat
Cochise

USA
823 Posts

Posted - 22 Oct 2015 :  9:43:22 PM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
I suspect not many guys have run a carb like that on this site Dave. My experience wasn't at all positive. I tried running a new Demon 850 double pumper, with the HP main body and annular boosters when I got my new combo running several years ago. 455 .035 over TH400 3.55 gears, ported KRE D's, ported matched Victor, Voodoo 705 cam with Rhoads. I could never get it right, I messed with it the entire first season and it had a bog that I couldn't get rid of entirely. Switched to a bigger 1000 cfm DP with downleg boosters built by Pro Systems that was the ticket for me. You're welcome to buy it off me if you're interested, I would order new metering blocks which was my next move with that carb. The annulars supposed to respond well with big cam engines with low idle vacuum so on my end the Rhoads lifters may have been counterproductive, but you're welcome to try it out on your setup. Shoot me an email if you want it, as I said it looks and is almost brand new with just one year of usage.

Pure Pontiac: learn it, live it, love it!
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GtoGuy32
Cochise

USA
842 Posts

Posted - 22 Oct 2015 :  11:03:46 PM  Show Profile  Reply with Quote
Hi Randall,

Interesting...How did the carb perform on the top end? Was it always low end, off idle issues? Does the carb have dual 30 cc accelerator pumps or a 50 cc on the secondary? (just curious)

I have messed with a few Demon carbs and haven't been overly impressed. I think if I do anything and thats a big if, I will likely stick with the AED unit. I have really liked the carb I am running now and has performed better than any other carb I have owned.

Im interested in knowing more about your issues with the carb so I can ask the guys at AED about similar issues and how their hardware differs to mitigate the problems.

Have you run your car at the track Randall? I am sure it is no slouch....
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Chicagogoat
Cochise

USA
823 Posts

Posted - 23 Oct 2015 :  07:07:22 AM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
The Demon carb has smaller accelerator pump diaphragms compared to the current Pro Systems unit with 50 cc pumps so I assume they're 30 cc. Demons need to be tweaked and modified a lot to make them perform well on any well built combo it goes on so it seems. I've only run 12.10's so far on 2 separate track outings and I suspect and hope to get in the very high 11's with my current set up. You may as well send your current AED carb in so they can change it up for you. I know you've pulled high 11 times so far but aren't you running a solid flat cam & manual trans?

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Chicagogoat
Cochise

USA
823 Posts

Posted - 23 Oct 2015 :  10:36:39 AM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
The carb was doggish throughout the rpm range and was particularly bad from mid-range to high rpm. I suspect the size (believe it or not) 850 wasn't enough capacity for my setup. If a 455 with unported 6X's runs perfect with an 850. I'd imagine that with ported aluminum heads, more compression and cam requires a bigger carb. So not an apples to apples comparison. I've read that the annulars help out rough idling big cam engines and are more responsive as well.

Pure Pontiac: learn it, live it, love it!
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GtoGuy32
Cochise

USA
842 Posts

Posted - 24 Oct 2015 :  12:19:40 AM  Show Profile  Reply with Quote
quote:
Originally posted by Chicagogoat

The Demon carb has smaller accelerator pump diaphragms compared to the current Pro Systems unit with 50 cc pumps so I assume they're 30 cc. Demons need to be tweaked and modified a lot to make them perform well on any well built combo it goes on so it seems. I've only run 12.10's so far on 2 separate track outings and I suspect and hope to get in the very high 11's with my current set up. You may as well send your current AED carb in so they can change it up for you. I know you've pulled high 11 times so far but aren't you running a solid flat cam & manual trans?



Hi Randall, I am running a solid roller cam with a 4 speed. I am sure your car has 11s in it. What was the 60 foot times and mile per hour? It's tough to get them to run at their full potential...
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GtoGuy32
Cochise

USA
842 Posts

Posted - 24 Oct 2015 :  12:23:46 AM  Show Profile  Reply with Quote
quote:
Originally posted by Chicagogoat

The carb was doggish throughout the rpm range and was particularly bad from mid-range to high rpm. I suspect the size (believe it or not) 850 wasn't enough capacity for my setup. If a 455 with unported 6X's runs perfect with an 850. I'd imagine that with ported aluminum heads, more compression and cam requires a bigger carb. So not an apples to apples comparison. I've read that the annulars help out rough idling big cam engines and are more responsive as well.



What is your head flow and what RPM are you shifting at? Do you feel like you have lost an throttle response by going to the bigger carb or does it still have a lot of snap?

As far as the Annular boosters...I am not too sure what the net gain will be just yet. Your info is in line with John from AED. If it is worth half a tenth, I won't go for it. If it is worth a tenth or two, I will consider if for sure. Tough to say....I'd love to see some dyne sheets or timeslips showing improvements.

I have David Vivards new Holley book coming. Perhaps that will have some useful info.
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Chicagogoat
Cochise

USA
823 Posts

Posted - 24 Oct 2015 :  08:52:18 AM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
aven't been able to fine my timeslips from this past summer but off the top of my head, I ran a 12.12 @109 and a 1.60 60'. That's with some tire spin out off the line. I discovered my posi was nearly shot afterwards and switched to a Detroit Trutrac diff in August so we'll see what it does next year.

The Pro Systems carb is a custom built unit. The paperwork I filled out about my combo was very comprehensive like if I was ordering a torque converter. It idles smoother, excellent throttle response and it pulls all the way to red line 6000 with no hiccups unlike the Demon which I could only reduce to symptoms and never really eliminate them. The PS carb has large dominator sized fuel passages in the metering blocks and custom high shear/signal downleg boosters according to the paperwork. I shift at around 5600 at the track for the best times, tried shifting @6000 but with Rhoads and a HFT it slows my run times a few tenths. I think I can pull some 11.90's. The cam is very small for what the heads flow 326cfm @.700 lift and I'm @ about .595 lift with that voodoo cam with 1.65 rockers. Ports are tall 2.4 X 1.2 so my next cam will be a tad more duration and more lift in the .650 range and will try a wider LSA like 112 or 114 for hopefully a ragged edge street combo. Not for a while though, my car is gonna get some body work done this off season and I'm pretty happy with the reliability and overall performance of the combo so far and wanna get my money's worth out of it.

Pure Pontiac: learn it, live it, love it!
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Chicagogoat
Cochise

USA
823 Posts

Posted - 24 Oct 2015 :  10:22:32 AM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
Sorry my recollection regarding my 60' time was incorrect. I found a few timeslips from 8 runs in early July this past summer.

RT .200
60' 1.707
1/8 7.690
MPH 88.46
1/4 12.165
MPH 108.90

As I said before, I feel that if I get a clean launch I can get into the 11's finally. The slowest I ran that day was a couple 12.3's when I had more than usual wheelspin. Best time that day was 12.10 which matched last summer's best.

Pure Pontiac: learn it, live it, love it!
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GtoGuy32
Cochise

USA
842 Posts

Posted - 25 Oct 2015 :  10:29:11 PM  Show Profile  Reply with Quote
Randall,

Those are good times. Your 60' will keep getting better. Maybe a little more tuning and you're there.

Whats the specs on the Voodoo 705 cam?

What is the elevation of your track?

-Dave
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Chicagogoat
Cochise

USA
823 Posts

Posted - 26 Oct 2015 :  10:09:24 AM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
My home track is Great Lakes Dragaway in the Racine/Kenosha area about 65 miles north of Chi. So pretty much the same altitude as you Dave.

This voodoo cam is the biggest one listed in their catalog but I gotta say seems pretty mild on this combo especially with Rhoads.

The cam specs:
Adv Dur- 284/292
Dur @.050- 241/249
Lift- .527/.548(with 1.5 rockers)
LSA 110

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GtoGuy32
Cochise

USA
842 Posts

Posted - 27 Oct 2015 :  11:06:22 PM  Show Profile  Reply with Quote
Randall,

Will you be changing up cams? I bet you could use more cam given the heads you have and everything else to feed it. Why didn't you go with 1.65 rockers and a little more lift?

I have been doing a lot of research on cams and picking as many brains as I can.

-Dave
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Chicagogoat
Cochise

USA
823 Posts

Posted - 28 Oct 2015 :  2:13:14 PM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
I just posted the specs of my cam the lift value is listed with the standard 1.5 rockers. I have Harland Sharp diamond series 1.65's which I'm told come in as much as 1.7 is what many have posted on the net. That pushes the actual intake lift close to .600 and exhaust over .600! That's one of two main reasons I choose this cam, one it's got decent lift and duration #'s for an off the shelf cam. Two it's a cheap HFT for my budget at the time so I can trade up to a bigger HR in the future.

If I went that route then I'd certainly buy into one of those SD comp HR's that are getting great reviews lately. Probably the road paver cam that's listed on SD's site.

Pure Pontiac: learn it, live it, love it!
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tjs44
Cochise

USA
412 Posts

Posted - 28 Oct 2015 :  7:37:53 PM  Show Profile  Reply with Quote
Let Dave help you with the cam pick!Tom
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clintww
Cochise

USA
582 Posts

Posted - 29 Oct 2015 :  10:50:47 PM  Show Profile  Reply with Quote
I love my AED carb. I had to do several adjustments to get it leaner, but it performs great. I would only consider a FAST system if I ever decided to change it. Got it close on the Dyno with one jet change, not the mains but the air bleeds. I believe mine is a 950 and has billet metering blocks. Even in MN it isn't hard to keep the car running without a choke. Just need to warm it some before putting it in gear.
I did open the idle air bleeds and reduced the squirter size down one size in the front and rear. Main jets were dead on.
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GtoGuy32
Cochise

USA
842 Posts

Posted - 29 Oct 2015 :  11:34:14 PM  Show Profile  Reply with Quote
quote:
Originally posted by tjs44

Let Dave help you with the cam pick!Tom



TJ, which Dave? Me or another Dave? I am no cam expert, but trying to learn more!
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Chicagogoat
Cochise

USA
823 Posts

Posted - 30 Oct 2015 :  12:35:37 PM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
Dave, he's talking about Dave Bischop owner of SD performance.

Clint, it's great to hear from ya. We both installed our motors a couple weeks apart in early '12. I'm glad you're loving your engine combo. I know all of you CVMS guys love AED carbs


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Cliff R
Cochise

USA
535 Posts

Posted - 23 Oct 2016 :  07:53:33 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
When properly tuned the down-leg booster carburetors will be fine. I use and prefer them to the annular booster variety. The annular boosters are more sensitive at very low throttle openings, but become a restriction and reduce cfm with any size venturi so you need to compensate for that.

I like at use 850 cfm carburetors on 455's past about 450hp. Even though the formula's for cfm requirements will tell you a 455 doesn't need that much cfm, they just flat work better and make better dyno numbers with the bigger carbs on them. I suppose this is due to the relatively "conservative" head flow and intake runner cross-section of the Pontiac cylinder head. The big 455 is also a poor air pump by design, under-square with long heavy rods and heavy internals. They are sucking pretty hard on the entire intake tract, and will see small carburetors as a restriction in the system.

A few years ago I spent a LOT of time with a custom built annular booster Holley, and at the same time tweaked and tuned my 4781-2 850 Holley to the brink of extinction, comparing both carburetors on the street and at the track on test and tune and private track rentals.

The ONLY thing I liked about the custom built annular booster carb was smoothness right off idle and in the "normal" driving range. It worked fine everyplace, but would not run the numbers at the track that my 4781-2 850 or 1977 Pontiac Q-jet would make.

We are only talking hundreths of seconds and less than 2mph differences, so not a deal breaker for sure, but I still favor the down-leg booster models after all the testing and decades of working with both types.....FWIW.....Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.
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Steve C.
Crazy Horse

1675 Posts

Posted - 23 Oct 2016 :  2:02:37 PM  Show Profile  Reply with Quote
Booster Shots

Yet another solution to the big carb for power versus smaller carb for driveability dilemma is to use a different-design booster venturi. Demon offers two different styles on some carbs: downleg boosters and annular boosters. Annular boosters are more responsive than downleg boosters. They pick up the vacuum signal quicker and start flowing sooner. While annular boosters offer more bottom-end driveability, they run richer on the top end and may siphon fuel out of the float bowls. The annular booster also decreases the carb's ultimate airflow potential because it has a larger physical presence within the venturi. For example, the Race Demon 950-cfm carb with annular boosters has the same venturi size as the 1,050-cfm Demon with downleg boosters.

Generally, annular boosters work best on 850-or-larger-cfm carbs to restore bottom-end performance on small-displacement engines or heavy vehicles. On lightweight cars and/or large-cubic-inch engines where bottom-end response isn't a problem, you're usually better off with a downleg-style booster.


Carbs: How Big Is Too Big?
http://www.hotrod.com/articles/selecting-right-carb/

This all said, I bought a carb with annular boosters and did not like it. It ran faster at the track with downleg-style boosters. It was custom carb based on a HP950 design. But it was a 7000 rpm combo at the time so I'm sure the annular boosters were the restriction.

Edited by - Steve C. on 23 Oct 2016 2:09:26 PM
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