Vacuum Secondaries

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Rebuild the 650 dp. I switched from a 750 vs to a 650 dp on my 340 and it ran so much better I totally quit using vs carbs from then on.
 
70aarcuda said:
Quick Fuel 63-1QFT Quick Set Adj. Sec. Housing

Quick Fuel 63-12QFT Adjustable Vacuum Secondary Die Cast Polished

http://documents.holley.com/99-19_63-1_quick_set_adj_instructions.pdf

quick fuel tech makes an adjustable vacuum canister..
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oh i like that...:)

never had any issues with the 780 vac secondary that was on my yellow dart.. damn thing ran awesome.. ended up going with a DP downt he road for the 4 corner idle and stuff it had but damn that that vac secondary carb run good..



.
 
I have a 3310 with one of those on it...played with it at the track....was able to knock a good tenth off the et...plus it looks good.
 
Hot Metal said:
Yes and if you had a decent DP on that those skinny tyres would be smoking like hell:D...thats the difference no "real" grunt.
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No, the 600 vac secondaries is enough, I had to let off because the Dart started to fishtail and I didn't want to loose control...

Many people over carb...

He put a 750 on it and took it off because the 600 ran better....
 
Smaller carbs will run ok thats a fact, its down to what you prefer, your level of skill in tuning a bigger carb and just what you are happy with from your combo and what you want it to do and how/where you do it. I can only give my actual experiences from the street and the results from the track and I for 1 would not want to drive a 340 around with a 600VS and have the car be a slug, thats why they came from the factory with an 800 thermo....and I ran 1 of those as well for a short time....nothing could touch the 850DP for shear power low down and up top and if tuned right its good as gold on the street. If all your doing is getting groceries with your car, then yes run a 600.
 
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I love TQs, any TQ. I think my 367 could use more than the 750DP that is on it now, but it won't be any faster on the street, cuz it already spins to well past any legal speed-limit in Manitoba.
I have never found this Holley to be "too big". On the primaries it's just like a regular 360-two barrel.
 
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DadsNewToy said:
I've got a 340 with a Holley 750. I was disappointed with the kick when I punched the throttle. I discovered with the help of a bobbie pin that the vacuum secondaries are not opening. I adjusted the throttle cable and gained more petal travel. The difference was amazing but the secondaries are still not opening. I've looked at Holley videos but still not 100% sure the vacuum lines are correct. The PCV valve hooks to the btm rear of the carb? What do I need for vacuum pressure to actuate? Is the 750 too big. Any suggestions are appreciated.
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Like was said - they're called vacuum secondary because the pressure differential between one of the venture, and atmospheric in the dashpot, is what opens the secondaries. They are the better choice for most automatic equipped street cars. But most people don't understand them or try to actually set them up properly. The springs are color-coded. You buy the assortment, and follow the instructions to get one that works as you need it. Usually that's the purple or the light yellow. When they are opening properly, you will not feel them open. If you feel them, they are opening too fast.
 
moper said:
Like was said - they're called vacuum secondary because the pressure differential between one of the venture, and atmospheric in the dashpot, is what opens the secondaries. They are the better choice for most automatic equipped street cars. But most people don't understand them or try to actually set them up properly. The springs are color-coded. You buy the assortment, and follow the instructions to get one that works as you need it. Usually that's the purple or the light yellow. When they are opening properly, you will not feel them open. If you feel them, they are opening too fast.
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Thank You ! I like it when someone who understands carbs chimes in.
IMO the holley 3310 is the best all around carb for an auto trans car.
I've ran AFB's AVS's and thermo's, none of which are as tunable as the 3310.
It only took me 30 years to figure it out.
 
I always thought if you felt them open, it was either because the primaries already ran out and the sec. were opening late. Or if you felt a bog, then a sudden rush that they were opening too soon, because you were waiting for the engine to catch up to the air and fuel the sec. was adding. Either way you really shouldn’t feel a transition.
But yes, the quick change kit and spring assortment was invaluable.
 
Hot Metal said:
Yes and if you had a decent DP on that those skinny tyres would be smoking like hell:D...thats the difference no "real" grunt.
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That's kind of where I was with my comment of am I missing something. Little hard pizza cutter tires on a V8 dart. Car would smoke the tires off with a 500cfm 2barrel.
 
Mattax said:
The bigger venturis of the 750 and up often can use the tube extension for stronger earlier signal.
Holley isn't going to do a video of that. lol :rolleyes:
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LOL, because then everybody will be purchasing 800/850/950 carbs to use on the 318/302/327/289 etc......
And be upset when it doesn't work.
 
Hot Metal said:
Smaller carbs will run ok thats a fact, its down to what you prefer, your level of skill in tuning a bigger carb and just what you are happy with from your combo and what you want it to do and how/where you do it. I can only give my actual experiences from the street and the results from the track and I for 1 would not want to drive a 340 around with a 600VS and have the car be a slug, thats why they came from the factory with an 800 thermo....and I ran 1 of those as well for a short time....nothing could touch the 850DP for shear power low down and up top and if tuned right its good as gold on the street. If all your doing is getting groceries with your car, then yes run a 600.
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If you know how to tune a carb, then you can do both "small" and "large" carbs.... :realcrazy:

That 600 vac secondary runs fine on the 340 and it's not a slug - it can break the tires loose from an idle with just stomping the pedal, no brake torque needed.... I could have kept spinning the tires in the video, but it started going sideways and I let off so I didn't loose control.... :steering:

What year did the 340 start with the thermoquad??? Now what carb was on them for the first 3 years???? :realcrazy:

If you under carb - you only choke it a little on the top end... If you over carb, then you drown it out through the whole RPM range.... :BangHead:

Where's the video of your car, let's see it run.... :bs_flag:
 
RogerRamRod said:
I always thought if you felt them open, it was either because the primaries already ran out and the sec. were opening late. Or if you felt a bog, then a sudden rush that they were opening too soon, because you were waiting for the engine to catch up to the air and fuel the sec. was adding. Either way you really shouldn’t feel a transition.
But yes, the quick change kit and spring assortment was invaluable.
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The bog is always because they opened too fast. The VS carbs only have the primary side accelerator pump. Once that pump has exhausted it's volume, only the airflow will create fuel flow through the secondaries. The bog is the lean spot that will happen until the airspeed is high enough through the secondaries to draw fuel out the boosters. I've seen many attempts to fix that - including adding the 50cc accelerator pump to the primary side, smaller shooters, etc. But the real fix is slowing the secondaries down.
Funniest part is the VS carbs are easier to set up than the DP. Most engines are simply passing way too much fuel with them, but the owners don't understand enough about how the carb and ignition work to really properly tune. That's why the plug-and-play EFI is such a huge market now and will only get bigger.
 
I had a tri-power setup on my 409 chebby with vacuum linkage to the front and rear carburetors. I was young and couldn't leave it alone so I took the vacuum linkage off and installed mechanical linkage to get the full effect of the three carburetors. OMG what a difference it made, now I had more motor than I had brakes-but that's another story.
I have to chime in that my street only Barracuda automatic loves the VS Holley I installed on an LD4B. I did install an Innovate wide band to help me tune it. I bought the quick change secondary spring change kit and studied the instructions to memory. Under all conditions I can watch the secondary's open and close on my wide band but because it has the correct springs in it you cannot feel any change in the fuel supply, it just keeps pulling and the wide band richens up. I know VS is not for everyone but it was the right choice for me and my build combination.
 
A to large of a carb actually runs lean. Not enough velocity/signal to pull fuel through it.
 
krazykuda said:
If you know how to tune a carb, then you can do both "small" and "large" carbs.... :realcrazy:

That 600 vac secondary runs fine on the 340 and it's not a slug - it can break the tires loose from an idle with just stomping the pedal, no brake torque needed.... I could have kept spinning the tires in the video, but it started going sideways and I let off so I didn't loose control.... :steering:

What year did the 340 start with the thermoquad??? Now what carb was on them for the first 3 years???? :realcrazy:

If you under carb - you only choke it a little on the top end... If you over carb, then you drown it out through the whole RPM range.... :BangHead:

Where's the video of your car, let's see it run.... :bs_flag:
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I don't have a video of the car as it was in 1986 Mr. Technical Editor who feels the need to make a perfectly good discussion and turn it into something approaching a slanging match. But just for your information....I raced at SPR for 10yrs, 8 of those years was with the 340 Cuda in Street Class, pictured below is my car on 1 of its launches with that way too big 850DP which was 2/10ths quicker in the 1/4 than the 750DP, which is no doubt too big as well.:rolleyes:
0cuda_launch_663.jpg
 
Thanks everyone for the wisdom. I've only had the Duster a couple of years so I don't know how fresh the engine is. I certainly am not going to red line it at 7000 rpm waiting for the secondaries to open. I don't want to be picking engine bits up off the pavement. But from what I read here the 750 VS will work fine for a mild street engine if tuned properly. I'm going to pull the vacuum pod off and ensure everything is OK with it. I'll see what spring is in it and then decide on getting the kit to go to a lighter spring.
The engine is running rich, by the carbon on the plugs. So I need to learn tuning the carb correctly. I am going to buy the rebuild kit for the 650 DP and get it in shape, just because. Maybe for sale on here.
 
rumblefish360 said:
LOL, because then everybody will be purchasing 800/850/950 carbs to use on the 318/302/327/289 etc......
And be upset when it doesn't work.
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My point was mostly that they often are missing a part that was always included in the earlier revisions -1, -2 in the days long before internet video... lol
 
Hot Metal said:
I don't have a video of the car as it was in 1986 Mr. Technical Editor who feels the need to make a perfectly good discussion and turn it into something approaching a slanging match.
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Slanging match???

You were the one that called the 340 Dart with a 600 vac secondaries a slug...

We built one that will spin the tires as long as you can hold it steady...

Not everybody does quarter mile... Many of us drive our cars on the street and want throttle response and a little fuel economy to go with it...
 
The "right" size carb will vary depending on the use of the engine. That's why 600, 750, 850, and 950+ may be the "right" carb. One needs to know how to tune them. Then match the combo and use with the size. The typical math basing cfm on displacement and rpm required really has very little to no bearing on sizing a carb. Especially when some carbs are dry flow rated, some are wet, and 2bbls are tested differently.
 
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