383 Carb: Annular or Down-leg boosters
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
383 Carb: Annular or Down-leg boosters
I have the 383, 9.9 CR, 284/292 adv dur cam, .543/.563 lift, RPM Air-gap intake, hilborn scoop, hooker super comp side pipes, RHS 200cc heads.
Ok, I have the Quick Fuel 750-PV vacuum sec down leg boosters on it. After reading Vizard's book, I think I should be running annular boosters not down leg. So I am thinking of going over to the Speed Demon 850 vac sec annular booster carb or the Mighty Demon 825 Cfm carb vac sec annular boosters. Or possibly the Quick Fuel Super Street 750 cfm mech sec annular boosters.
So opinions from all you carb guru's am I going to benefit from switching to annular boosters?
Ok, I have the Quick Fuel 750-PV vacuum sec down leg boosters on it. After reading Vizard's book, I think I should be running annular boosters not down leg. So I am thinking of going over to the Speed Demon 850 vac sec annular booster carb or the Mighty Demon 825 Cfm carb vac sec annular boosters. Or possibly the Quick Fuel Super Street 750 cfm mech sec annular boosters.
So opinions from all you carb guru's am I going to benefit from switching to annular boosters?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Read this. If you're any less confused than I was, good. If not, do what I did. Call them and ask!!
http://www.gnetworks.com/v4files/bar...0Questions.pdf
http://www.gnetworks.com/v4files/bar...0Questions.pdf
Pro
Joined: Apr 2006
Posts: 733
Likes: 1
From: Coquitlam British Columbia
Fyi.
King not sure if you are aware but Barry grant now makes a 750 annular speed demon as well, that is of course if you did not want to step up to the 850.
750 Anunular Speed Demon
#1402020 750 mechanical
#1402020VE VS
ikwhite
750 Anunular Speed Demon
#1402020 750 mechanical
#1402020VE VS
ikwhite
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
Any more opinions on annular vs down leg? I just got off the phone with BG Demon and they told me to run the down leg booster Mighty Demon 650 vacuum secondary carb. He claimed it will flow up and over 800 cfm as is. He also stated that since the vette is a lighter vehicle it would benefit more from a down leg then an annular booster carb. Lars I need you buddy!
Last edited by King Lear; Feb 22, 2007 at 11:37 AM.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
What is wrong with your quick fuel carb? Change carb type does not fix problems magically. You always have to do some tweaking.
I have been running a modified Speed demon from day one on my 383. IMO - VS carbs have some advantages and a sub 6500 rpm 383 would run fine with 650 cfm.
IMO - annular dist carbs
I have been running a modified Speed demon from day one on my 383. IMO - VS carbs have some advantages and a sub 6500 rpm 383 would run fine with 650 cfm.
IMO - annular dist carbs
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
What is wrong with your quick fuel carb? Change carb type does not fix problems magically. You always have to do some tweaking.
I have been running a modified Speed demon from day one on my 383. IMO - VS carbs have some advantages and a sub 6500 rpm 383 would run fine with 650 cfm.
IMO - annular dist carbs
I have been running a modified Speed demon from day one on my 383. IMO - VS carbs have some advantages and a sub 6500 rpm 383 would run fine with 650 cfm.
IMO - annular dist carbs
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
your vacuum would require a 6.5 PV. The secondary air bleed will determine the jet size for the secondaries, but 82 IMO is probably on the rich side.
The below 2000 bog has alot to do with the initial position of setting the throttle blade with .020 of the x-fer slot uncovered and you have to have the squirter arm set so tight that even the smallest throttle movement causesgas dribble.
Is you cam an h-flat?
The below 2000 bog has alot to do with the initial position of setting the throttle blade with .020 of the x-fer slot uncovered and you have to have the squirter arm set so tight that even the smallest throttle movement causesgas dribble.
Is you cam an h-flat?
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Any more opinions on annular vs down leg? I just got off the phone with BG Demon and they told me to run the down leg booster Mighty Demon 650 vacuum secondary carb. He claimed it will flow up and over 800 cfm as is. He also stated that since the vette is a lighter vehicle it would benefit more from a down leg then an annular booster carb. Lars I need you buddy!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
your vacuum would require a 6.5 PV. The secondary air bleed will determine the jet size for the secondaries, but 82 IMO is probably on the rich side.
The below 2000 bog has alot to do with the initial position of setting the throttle blade with .020 of the x-fer slot uncovered and you have to have the squirter arm set so tight that even the smallest throttle movement causesgas dribble.
Is you cam an h-flat?
The below 2000 bog has alot to do with the initial position of setting the throttle blade with .020 of the x-fer slot uncovered and you have to have the squirter arm set so tight that even the smallest throttle movement causesgas dribble.
Is you cam an h-flat?
I am going to wait until I get it back from the builder with the new heads. Right now it is at 9.2 CR and 6.7 dcr(wow) with a .057 quench with 160cc Pro Comp heads.
When I get it back I will be at 9.92 CR and 7.79 DCR and a .042 quench with 200cc RHS Pro Action heads. I think the adjustments I am making are greatly going to improve the performance of the car and change the whole booster signal.
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
Interesting. When I talked to them about my combo he like the 825 Might demon which I am running and said that the annular booster would be more driveable. I might give up 5 HP on top but the mid range and driveability would be better. Also I asked about the flow numbers and said an 850 flows 850 and a 650 flows 650. If I converted my 825 to annular boosters it might knock off 25 cfm due to the different boosters. A lot depends on who you talk to there. Call a different person and you might get a different answer.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
HR-284-2S-12 IG
Your cam is extreemly mild for a 383. I would expect 14+ inches of vacuum at a 800-900 idle rpm. I have bouncy 11 inches with 14 degrees more intake duration than you on a solid roller with a single plane intake
I would set the timing to 16 initial and if those heads have modern fast burn chambers recourve the dist. to a max of 32-34 degrees total all in by 3000 rpm.
Your cam is extreemly mild for a 383. I would expect 14+ inches of vacuum at a 800-900 idle rpm. I have bouncy 11 inches with 14 degrees more intake duration than you on a solid roller with a single plane intake
I would set the timing to 16 initial and if those heads have modern fast burn chambers recourve the dist. to a max of 32-34 degrees total all in by 3000 rpm.
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
HR-284-2S-12 IG
Your cam is extreemly mild for a 383. I would expect 14+ inches of vacuum at a 800-900 idle rpm. I have bouncy 11 inches with 14 degrees more intake duration than you on a solid roller with a single plane intake
I would set the timing to 16 initial and if those heads have modern fast burn chambers recourve the dist. to a max of 32-34 degrees total all in by 3000 rpm.
Your cam is extreemly mild for a 383. I would expect 14+ inches of vacuum at a 800-900 idle rpm. I have bouncy 11 inches with 14 degrees more intake duration than you on a solid roller with a single plane intake
I would set the timing to 16 initial and if those heads have modern fast burn chambers recourve the dist. to a max of 32-34 degrees total all in by 3000 rpm.
Last edited by King Lear; Feb 22, 2007 at 03:29 PM.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
there is a little formula for a power valve and it is basically two inches less than your lowest idle reading. Like when you put it in gear with the brake on. The higher initial timing really brings up the vacuum.
I also had a 3500+ stall convert when I had an auto tranny so i didn't really ever have an rpm drop in gear.
You might try driving with the vac. gauge taped to window so you can see how the vacuum runs. You don't want the power valve to dump fuel on small throttle changes while driving. Just when you hit it. I would think that it would be hard to 3.5 inches unless you really open it up.
I also had a 3500+ stall convert when I had an auto tranny so i didn't really ever have an rpm drop in gear.
You might try driving with the vac. gauge taped to window so you can see how the vacuum runs. You don't want the power valve to dump fuel on small throttle changes while driving. Just when you hit it. I would think that it would be hard to 3.5 inches unless you really open it up.
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
there is a little formula for a power valve and it is basically two inches less than your lowest idle reading. Like when you put it in gear with the brake on. The higher initial timing really brings up the vacuum.
I also had a 3500+ stall convert when I had an auto tranny so i didn't really ever have an rpm drop in gear.
You might try driving with the vac. gauge taped to window so you can see how the vacuum runs. You don't want the power valve to dump fuel on small throttle changes while driving. Just when you hit it. I would think that it would be hard to 3.5 inches unless you really open it up.
I also had a 3500+ stall convert when I had an auto tranny so i didn't really ever have an rpm drop in gear.
You might try driving with the vac. gauge taped to window so you can see how the vacuum runs. You don't want the power valve to dump fuel on small throttle changes while driving. Just when you hit it. I would think that it would be hard to 3.5 inches unless you really open it up.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Bump it up to 15? What are you at now. I run my initial at 18 to 20 With my cam I can barely to get it to run at 16 or below. Mine idles at about 950 plus or minus 100 rpm. I am running a stick though.
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
Thanks, that is what I am leading toward the Speed Demon 750 annular, I think I am going to stick with mech sec. I seem to get better performance out of them even on an automatic.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Race Director
Joined: Apr 2000
Posts: 17,665
Likes: 194
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Don't know who you were talking to at BG but I have talked to a reliable source there and he told me BG carbs are rated different than Holley carbs. My 825 Race Demon flows 975cfm according to him.
Anyway annular discharge boosters was one of the best mods I have ever done. Much crisper throttle response and more torque, I would recommend anyone to do it. The new 750 Demon with annular boosters would work great
Anyway annular discharge boosters was one of the best mods I have ever done. Much crisper throttle response and more torque, I would recommend anyone to do it. The new 750 Demon with annular boosters would work great
Thread Starter
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
Don't know who you were talking to at BG but I have talked to a reliable source there and he told me BG carbs are rated different than Holley carbs. My 825 Race Demon flows 975cfm according to him.
Anyway annular discharge boosters was one of the best mods I have ever done. Much crisper throttle response and more torque, I would recommend anyone to do it. The new 750 Demon with annular boosters would work great
Anyway annular discharge boosters was one of the best mods I have ever done. Much crisper throttle response and more torque, I would recommend anyone to do it. The new 750 Demon with annular boosters would work great