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Dual Quad tuning tips?

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TheGreatPumpkin
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Dual Quad tuning tips?

Post by TheGreatPumpkin »

Hello all - I'm new here. Been reading as much as possible about tuning Holley 1850C carbs in a dual quad configuration - there's so much to know and learn. I have a solid understanding of how carbs and engines work (engineering background) but I'm short on experience and would like to stick to old-school techniques and tuning. I have a combo that starts and idles fine, a bit rich, and would like to know how to address tuning - will be starting to drive and tune next week when I have some free time, and would like to know what to address right off the bat. Here's the combo - mild, but a solid test bed for my ideas and stuff

466ci Ford, 9:1 pump gas, older rebuild and now a mild street engine
D3VEs with medium porting
Lunati Voodoo 268/276 hyd flat tappet (227/233@50, .552/.564)
Blue Thunder CJ dual quad intake with 1850Cs
FPA headers
3 inch exhaust with x-pipe
Roller rockers, stock oil pump, 20w50, Ford Motorsports water pump, etc, nothing else special. In a 1970 Torino GT with coilovers, Cal Tracs, panhard bar, Toploader, etc.

The dual quad intake and carbs is new, mostly for looks, and I've never tuned a setup like this before. Anything I should do right away? Carbs are modded with screw in bleeds and vacuum cans are connected to each other. I'll update this post as soon as I get some driving done. Have multiple vacuum gauges and a good wideband gauge also...
Walter R. Malik
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Re: Dual Quad tuning tips?

Post by Walter R. Malik »

TheGreatPumpkin wrote: Fri Aug 05, 2022 4:12 am Hello all - I'm new here. Been reading as much as possible about tuning Holley 1850C carbs in a dual quad configuration - there's so much to know and learn. I have a solid understanding of how carbs and engines work (engineering background) but I'm short on experience and would like to stick to old-school techniques and tuning. I have a combo that starts and idles fine, a bit rich, and would like to know how to address tuning - will be starting to drive and tune next week when I have some free time, and would like to know what to address right off the bat. Here's the combo - mild, but a solid test bed for my ideas and stuff

466ci Ford, 9:1 pump gas, older rebuild and now a mild street engine
D3VEs with medium porting
Lunati Voodoo 268/276 hyd flat tappet (227/233@50, .552/.564)
Blue Thunder CJ dual quad intake with 1850Cs
FPA headers
3 inch exhaust with x-pipe
Roller rockers, stock oil pump, 20w50, Ford Motorsports water pump, etc, nothing else special. In a 1970 Torino GT with coilovers, Cal Tracs, panhard bar, Toploader, etc.

The dual quad intake and carbs is new, mostly for looks, and I've never tuned a setup like this before. Anything I should do right away? Carbs are modded with screw in bleeds and vacuum cans are connected to each other. I'll update this post as soon as I get some driving done. Have multiple vacuum gauges and a good wideband gauge also...
Their tuning is slightly different depending upon whether they are "staged", (and which one is ahead of the other), or both open at the same time.
Why are you using 20W-50 oil ...?
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

Walter R. Malik wrote: Fri Aug 05, 2022 11:40 am Their tuning is slightly different depending upon whether they are "staged", (and which one is ahead of the other), or both open at the same time.
Why are you using 20W-50 oil ...?
They are 1:1 with each other. The oil? Habit. That's what the guy I bought it from (in 2003) ran in it and I only recently got a good oil pressure gauge, so we'll see how it does
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Re: Dual Quad tuning tips?

Post by Walter R. Malik »

TheGreatPumpkin wrote: Fri Aug 05, 2022 11:46 am
Walter R. Malik wrote: Fri Aug 05, 2022 11:40 am Their tuning is slightly different depending upon whether they are "staged", (and which one is ahead of the other), or both open at the same time.
Why are you using 20W-50 oil ...?
They are 1:1 with each other. The oil? Habit. That's what the guy I bought it from (in 2003) ran in it and I only recently got a good oil pressure gauge, so we'll see how it does
With 1 to 1 they should both be tuned the same, as if there was only 1 carburetor.
The secondary idle screws should be set at only about 1/4 turn from fully closed; just so the secondary plates don't stick in the bores.
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

Re: the secondary throttle blades, did that, learned that just last week
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Re: Dual Quad tuning tips?

Post by tjs44 »

I would set them up progressive like the factory did.IMO,WAY more EZ to drive.Tom
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

tjs44 wrote: Fri Aug 05, 2022 2:46 pm I would set them up progressive like the factory did.IMO,WAY more EZ to drive.Tom
I'm concerned about the low speed/cruise fuel distribution if I set them that way, since it's a dual plane intake. There's no reason they can be tuned for good throttle response 1:1, I suspect I'll have to reduce the air bleeds and IFRs a bit.

I did have one question - initially I set these up with quick fuel billet metering blocks and plates, but the blocks are so thick that they made the carbs contact each other at the bowls when mounted. They fit, but they hit. Can I run them like that or will they expand and crack when they get hot?
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Re: Dual Quad tuning tips?

Post by tjs44 »

I have been running 2-4s since 1962,on a pontiac but no matter if a dual plane,single plane or tunnel ram they drive great on the front venturies of the rear carbs.I only went solid when racing the car.A set of factory med riser holleys would have been perfect.KISS seems to always work out.FWIW,Tom
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

tjs44 wrote: Fri Aug 05, 2022 7:46 pm I have been running 2-4s since 1962,on a pontiac but no matter if a dual plane,single plane or tunnel ram they drive great on the front venturies of the rear carbs.I only went solid when racing the car.A set of factory med riser holleys would have been perfect.KISS seems to always work out.FWIW,Tom
I'm trying my best to KISS, believe me!
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Re: Dual Quad tuning tips?

Post by ClassAct »

TheGreatPumpkin wrote: Fri Aug 05, 2022 3:31 pm
tjs44 wrote: Fri Aug 05, 2022 2:46 pm I would set them up progressive like the factory did.IMO,WAY more EZ to drive.Tom
I'm concerned about the low speed/cruise fuel distribution if I set them that way, since it's a dual plane intake. There's no reason they can be tuned for good throttle response 1:1, I suspect I'll have to reduce the air bleeds and IFRs a bit.

I did have one question - initially I set these up with quick fuel billet metering blocks and plates, but the blocks are so thick that they made the carbs contact each other at the bowls when mounted. They fit, but they hit. Can I run them like that or will they expand and crack when they get hot?


Turn the carbs sideways. It’s a pain in the ass with in-line carbs. You can run them 1:1 if you want. By that I mean open all 8 at once. I have never liked running in line carbs and staging one carb ahead of the other.
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

ClassAct wrote: Fri Aug 05, 2022 9:40 pm
TheGreatPumpkin wrote: Fri Aug 05, 2022 3:31 pm
tjs44 wrote: Fri Aug 05, 2022 2:46 pm I would set them up progressive like the factory did.IMO,WAY more EZ to drive.Tom
I'm concerned about the low speed/cruise fuel distribution if I set them that way, since it's a dual plane intake. There's no reason they can be tuned for good throttle response 1:1, I suspect I'll have to reduce the air bleeds and IFRs a bit.

I did have one question - initially I set these up with quick fuel billet metering blocks and plates, but the blocks are so thick that they made the carbs contact each other at the bowls when mounted. They fit, but they hit. Can I run them like that or will they expand and crack when they get hot?


Turn the carbs sideways. It’s a pain in the ass with in-line carbs. You can run them 1:1 if you want. By that I mean open all 8 at once. I have never liked running in line carbs and staging one carb ahead of the other.
Guys just to clarify, the carbs are 1:1 with each other but the carbs themselves are the stock vacuum secondary linkage

Can't go sideways, won't idle on half the manifold then
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Re: Dual Quad tuning tips?

Post by F-BIRD'88 »

If yiu are worried about the 2 carvs bowls touching then once you dial in the metering block on the rear primary carb you can copy that new fiund metering back to the stock holley metering block, that you say is a hair thinner.
As long as its not a press fit between the 2 carbs I don't see a issue with them touching slightly.

Keep your mind open to the staged progressive throttle linkage set up for "Dual Quad" street driving.. on a dual plane type intake.
Use what works best.
Too bad there is not a HP body version /or upgrade kit (VS + down leg style boosters) of these 600 cfm VS carbs with the small fuel bowls.
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Re: Dual Quad tuning tips?

Post by ClassAct »

TheGreatPumpkin wrote: Fri Aug 05, 2022 9:44 pm
ClassAct wrote: Fri Aug 05, 2022 9:40 pm
TheGreatPumpkin wrote: Fri Aug 05, 2022 3:31 pm

I'm concerned about the low speed/cruise fuel distribution if I set them that way, since it's a dual plane intake. There's no reason they can be tuned for good throttle response 1:1, I suspect I'll have to reduce the air bleeds and IFRs a bit.

I did have one question - initially I set these up with quick fuel billet metering blocks and plates, but the blocks are so thick that they made the carbs contact each other at the bowls when mounted. They fit, but they hit. Can I run them like that or will they expand and crack when they get hot?


Turn the carbs sideways. It’s a pain in the ass with in-line carbs. You can run them 1:1 if you want. By that I mean open all 8 at once. I have never liked running in line carbs and staging one carb ahead of the other.
Guys just to clarify, the carbs are 1:1 with each other but the carbs themselves are the stock vacuum secondary linkage

Can't go sideways, won't idle on half the manifold then
Who told you that? I don’t run in-line carbs. My shit idles. That’s ridiculous.
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

ClassAct wrote: Fri Aug 05, 2022 11:06 pm
TheGreatPumpkin wrote: Fri Aug 05, 2022 9:44 pm
ClassAct wrote: Fri Aug 05, 2022 9:40 pm



Turn the carbs sideways. It’s a pain in the ass with in-line carbs. You can run them 1:1 if you want. By that I mean open all 8 at once. I have never liked running in line carbs and staging one carb ahead of the other.
Guys just to clarify, the carbs are 1:1 with each other but the carbs themselves are the stock vacuum secondary linkage

Can't go sideways, won't idle on half the manifold then
Who told you that? I don’t run in-line carbs. My shit idles. That’s ridiculous.
Ok, ok, noted. Will keep an open mind
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Re: Dual Quad tuning tips?

Post by Tom68 »

ClassAct wrote: Fri Aug 05, 2022 11:06 pm
Who told you that? I don’t run in-line carbs. My shit idles. That’s ridiculous.
Separated Dual Plane. Common sense told him that. Unless he face them in opposite directions.
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