Re: Would/do you use a spread bore carb?
[Re: Guitar Jones]
#2926079
05/24/21 09:55 AM
05/24/21 09:55 AM
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Joined: Jan 2003
Posts: 12,814 Benton, IL.
DaveRS23
Master of nothing...
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Master of nothing...
Joined: Jan 2003
Posts: 12,814
Benton, IL.
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As for vacuum secondaries, I have never found a need for anything other than vacuum secondaries on the street. If you are considering the street demon it only comes with those. You may have 'never found a need for anything other than vacuum secondaries on the street', but our favorite manufacturer (Mopar) used mechanical secondaries more than anything else. Only the later Holleys used vacuum. ALL of the Carters (AFBs, AVSs, Thermoquads) used mechanical secondaries. And that was on everything from 273s to Hemis. Not totally accurate, while it's true the actual throttle butterflies were mechanically actuated, the air door in the top prevented them from actually doing anything until that air valve opened as the engines ability to ingest the extra air and fuel increased creating the same effect as a Holley type of vacuum actuated carb. So TQs, QJs, AFBs and AVSs are really considered to be vacuum secondary carbs as the secondaries only work as the engine demands and not the throttle. Not totally accurate. The secondary air door has an impact on air flow only IF they are adjusted a certain way. While we all understand the function of the secondary air doors (well, maybe some do and some don't) this is the first time I have heard anyone describe the Carters as vacuum secondary carbs. There are a few AFBs that actually used a vacuum pod to operate the secondaries and there are AFBs without secondary air doors.Twist it any way you want to make an argument, but the secondary throttle plates are opened by direct linkage from the primaries (for the vast majority of Carters) and the air doors are above the boosters on most models so that they are as much an enrichment device as they are an air flow control device. The air doors have an impact on the secondaries' operation, but they do not control them. Primary control rests with the linkage and linkage alone. Mopar's Carters were not vacuum secondary carbs.
Master, again and still
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Re: Would/do you use a spread bore carb?
[Re: DaveRS23]
#2926294
05/24/21 09:04 PM
05/24/21 09:04 PM
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Joined: Dec 2009
Posts: 21,066 in a cattle trailer down by th...
Guitar Jones
Paddle faster! I hear banjo music!
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Paddle faster! I hear banjo music!
Joined: Dec 2009
Posts: 21,066
in a cattle trailer down by th...
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I said they are considered vacuum secondary carbs because the secondaries function off of engine demand and not strictly off of the throttle plate butterflies. Twist however you want but look them up on Summit or Jegs and see if they are listed as mechanical or vacuum secondary carbs. You could also try pointing out where the secondary accelerator pump squirters are on those carbs.
"Come get your wife"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion. '74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Front and rear disc and hydroboost conversion. 2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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Re: Would/do you use a spread bore carb?
[Re: moparx]
#2926312
05/24/21 10:45 PM
05/24/21 10:45 PM
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Joined: Sep 2005
Posts: 632 Deep DEEP SOUTH
LAD 524
mopar
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mopar
Joined: Sep 2005
Posts: 632
Deep DEEP SOUTH
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just love those thermoquads ! i have always wanted to try a tunnel ram with twin thermoquads, but have never had the opportunity to do so. You mean like this ?
Last edited by LAD 524; 05/28/21 04:36 AM.
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Re: Would/do you use a spread bore carb?
[Re: Guitar Jones]
#2926405
05/25/21 09:27 AM
05/25/21 09:27 AM
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Joined: Jan 2003
Posts: 12,814 Benton, IL.
DaveRS23
Master of nothing...
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Master of nothing...
Joined: Jan 2003
Posts: 12,814
Benton, IL.
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I said they are considered vacuum secondary carbs because the secondaries function off of engine demand and not strictly off of the throttle plate butterflies. Twist however you want but look them up on Summit or Jegs and see if they are listed as mechanical or vacuum secondary carbs. You could also try pointing out where the secondary accelerator pump squirters are on those carbs. So you use sales ads for your technical information? That helps explain your opinion on this. And I have no idea what you are trying to say about the pump squirters. Did you read that in an advertisement, too? Bottom line; the secondary air door is not essential to the operation of the secondaries. It can be an asset and certainly helps in some applications but is not an absolute necessity.
Master, again and still
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Re: Would/do you use a spread bore carb?
[Re: DaveRS23]
#2926628
05/25/21 08:13 PM
05/25/21 08:13 PM
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Joined: May 2019
Posts: 6,511 nowhere
Sniper
master
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master
Joined: May 2019
Posts: 6,511
nowhere
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I said they are considered vacuum secondary carbs because the secondaries function off of engine demand and not strictly off of the throttle plate butterflies. Twist however you want but look them up on Summit or Jegs and see if they are listed as mechanical or vacuum secondary carbs. You could also try pointing out where the secondary accelerator pump squirters are on those carbs. So you use sales ads for your technical information? That helps explain your opinion on this. And I have no idea what you are trying to say about the pump squirters. Did you read that in an advertisement, too? Bottom line; the secondary air door is not essential to the operation of the secondaries. It can be an asset and certainly helps in some applications but is not an absolute necessity. Straight out of the Carter manual for the TQ
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Re: Would/do you use a spread bore carb?
[Re: Sniper]
#2926637
05/25/21 08:32 PM
05/25/21 08:32 PM
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Joined: Jan 2003
Posts: 12,814 Benton, IL.
DaveRS23
Master of nothing...
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Master of nothing...
Joined: Jan 2003
Posts: 12,814
Benton, IL.
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Mechanical secondaries with a variable venturi feature. Good points, straight from Carter and not from a sales brochure.
Venturi: A Venturi is a system for speeding the flow of the fluid, by constricting it in a cone shaped tube. In the restriction the fluid must increase its velocity reducing its pressure and producing a partial vacuum. As the fluid leaves the constriction, its pressure increases back to the ambient or pipe level.
A venturi DOES NOT control the secondary operation. It aids it.
Thank you.
Master, again and still
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Re: Would/do you use a spread bore carb?
[Re: Hangtowner]
#2928625
05/30/21 07:43 PM
05/30/21 07:43 PM
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Joined: Jan 2011
Posts: 16,096 Central Florida
larrymopar360
OP
Stud Muffin
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OP
Stud Muffin
Joined: Jan 2011
Posts: 16,096
Central Florida
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I wish I knew of a chassis dyno here in town. I guess it's possible there's one I don't know of but never heard of one and we're not that big. Also isn't a street demon a Holley? I guess he meant same design not "owned by".
Facts are stubborn things.
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Re: Would/do you use a spread bore carb?
[Re: larrymopar360]
#2928695
05/30/21 09:47 PM
05/30/21 09:47 PM
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Joined: Jan 2003
Posts: 1,793 Windsor, ON, Canada
Diplomat360
top fuel
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top fuel
Joined: Jan 2003
Posts: 1,793
Windsor, ON, Canada
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Larry,
If you score a 9800 series TQ I will set it up for you. The attached electric choke takes care of running this beast with any intake you chose.
Anyways, they are out there, I see them occasionally pop up on eBag...not too often, but they can be found.
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Re: Would/do you use a spread bore carb?
[Re: Diplomat360]
#2928751
05/31/21 02:41 AM
05/31/21 02:41 AM
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Joined: Feb 2006
Posts: 608 TN
1DGEMAN
mopar
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mopar
Joined: Feb 2006
Posts: 608
TN
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Larry,
If you score a 9800 series TQ I will set it up for you. The attached electric choke takes care of running this beast with any intake you chose.
Anyways, they are out there, I see them occasionally pop up on eBag...not too often, but they can be found. I have a 9801and a 9811
Real Men shift for themselves
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Re: Would/do you use a spread bore carb?
[Re: DaveRS23]
#2928772
05/31/21 08:20 AM
05/31/21 08:20 AM
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Joined: Dec 2009
Posts: 21,066 in a cattle trailer down by th...
Guitar Jones
Paddle faster! I hear banjo music!
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Paddle faster! I hear banjo music!
Joined: Dec 2009
Posts: 21,066
in a cattle trailer down by th...
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Mechanical secondaries with a variable venturi feature. Good points, straight from Carter and not from a sales brochure.
Venturi: A Venturi is a system for speeding the flow of the fluid, by constricting it in a cone shaped tube. In the restriction the fluid must increase its velocity reducing its pressure and producing a partial vacuum. As the fluid leaves the constriction, its pressure increases back to the ambient or pipe level.
A venturi DOES NOT control the secondary operation. It aids it.
Thank you. Read the first and second sentence in snipers attachment again. That is what I'm saying. You can't open those secondaries mechanically without some sort of restriction to delay the intake of additional air or you need a secondary accelerator pump shot to prevent a huge backfire and most likely stalling the engine. In other words, vacuum secondary carbs allow the intake of extra air and fuel as the engine demands it, not as a function of the mechanical linkage alone. Block that secondary air valve fully open and then tell us how those mechanical secondaries work. I don't know why you want to argue this point, it's really useless and unproductive, so whatever, I'm done.
"Come get your wife"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion. '74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Front and rear disc and hydroboost conversion. 2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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Re: Would/do you use a spread bore carb?
[Re: Hangtowner]
#2929197
06/01/21 03:12 PM
06/01/21 03:12 PM
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Joined: Jan 2011
Posts: 16,096 Central Florida
larrymopar360
OP
Stud Muffin
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OP
Stud Muffin
Joined: Jan 2011
Posts: 16,096
Central Florida
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Holley owns Demon now, but the only thing in common is the secondary jets. I was just about to ask that. One thing I really like about the new design factors of Demon are the large bowls helping with starts after sitting for several days. Damn 10% ethanol. I get about three days parked and after that have to pour gas down carb. Would rather not have to install another pump.
Facts are stubborn things.
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Re: Would/do you use a spread bore carb?
[Re: larrymopar360]
#2929321
06/01/21 09:16 PM
06/01/21 09:16 PM
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Joined: Jan 2003
Posts: 12,814 Benton, IL.
DaveRS23
Master of nothing...
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Master of nothing...
Joined: Jan 2003
Posts: 12,814
Benton, IL.
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One MAJOR improvement over the Thermoquads is that there is no gasket at the bottom of the fuel bowl.
Master, again and still
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