2bbl conversion -- worth it?

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mvh

mvh

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Hi! I've been on FABO for a long time, but I'm new to slant sixes. So, this 67 Barracuda convertible came with a few boxes of parts, including a Carter BBD and the 2bbl manifolds, newly painted, and the air cleaner base. It seems clear that my father was contemplating swapping out the Holley 1920 at one time. What I want to know is, what are the pros and cons? Any other parts needed? As far as I know the rest of the motor is stock, other than a Pertronix distributor.
 
You will need the kickdown linkage for the swap. It will make a noticeable difference in performance and is said to actually improve your fuel economy.
 
I did the swap. When i had the 1bbl set up i was getting 22mpg then after when i went 2bbl i get 17 mpg it did make a noticeable difference in power though way easier getting on the freeway and cutting people off hahahahhahah
 
Yeah, I don't know where the "improve fuel economy" myth came from, but that's what it is. A myth. Since the 2 barrel is not a staged one and both barrels open simultaneously, mileage will certainly go down.

IMO, unless you are making several other modifications at the same time, such as headers, maybe milling the head and adding a performance camshaft, the gains you will get just from the 2 barrel carburetor alone and the needed larger exhaust will be noticeable, but not impressive. IMO you will get a bigger decrease in mileage than increase in power.
 
RustyRatRod said:
Yeah, I don't know where the "improve fuel economy" myth came from, but that's what it is. A myth. Since the 2 barrel is not a staged one and both barrels open simultaneously, mileage will certainly go down.

IMO, unless you are making several other modifications at the same time, such as headers, maybe milling the head and adding a performance camshaft, the gains you will get just from the 2 barrel carburetor alone and the needed larger exhaust will be noticeable, but not impressive. IMO you will get a bigger decrease in mileage than increase in power.
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Rusty is dead on its all a damn myth.. i meet a guy who told me he went super six and was getting 15 mpg then went four bbl with a holley and got 20mpg.. i think he said he had a 550 cfm or 600 not sure i want to try it out now
 
My family had several Darts with /6's, and out of the auto trans cars, my mom's 1980 Aspen with the 2 BBL Super Six got better gas mileage than her 1969 Dart 1 BBL. I understand that the 1980 Aspen had the lean burn system, and it certainly had a locking torque converter, and I am 99% certain that it had a lower rear axle ratio, so those are unknown factors in the equation. The Aspen was also significantly 'perkier' than the 1 BBL, even though it was a bit heavier.

Results are going to depend on a lot of factors. Just the rear axle ratio, and the resulting RPM's on the freeway will make a big difference, as that sets the cruise vacuum level and if the power valve in the carb is open while cruising. And, how you drive it and how you tune it up makes a big difference. So without knowing those factors for a given situation, like for Slantsix64's car, you can't draw broad conclusions from one setup.
 
i did a 2 bbl on a 64 dart. in 1974. the big thing with a 2 bbl is that the carb throttle shaft should be parallel to the crank shaft. unlike how chrysler did it. and the cam be a pre smog camshaft. but the most important thing be that the throttle NOT stick wide open. IMHO the stock pistons when over reved will wipe out the piston rings. had that happened two times to me.
 
Actually, the 71-77 camshaft was the most "radical" installed in the 225. There are several aftermarket camshafts available. Check here and over at SlantSix.org.

Good luck finding an intake that will allow the throttle shaft to be installed parallel to the crankshaft. Most I have seen are perpendicular.

As for kickdown linkages, consider either a Lokar or Buchillon Performance kickdown cable.
 
Thanks for all the info. Ah, I hadn't realized that the 2bbl wasn't progressive... so what's the point of it, then? Better WOT performance, I guess. If it were progressive, I would expect better mileage than a 1bbl, because the primary could be set for economy, and the secondary for power. But if it's not, then I can see that it will just use more gas when you step on it (to look at it the simplest way possible).
OK, I also have a 2-to-4bbl converter plate. What if I used a Carter AFB? It has pretty small primaries -- I guess I'd want to compare them to the 2bbl. I am just bringing this up for discussion -- I am not really contemplating hotrodding this six, at least not until I sort out all the little niggling issues (why the wipers don't work, dash lights are so dim, etc.).
 
nm9stheham said:
My family had several Darts with /6's, and out of the auto trans cars, my mom's 1980 Aspen with the 2 BBL Super Six got better gas mileage than her 1969 Dart 1 BBL. I understand that the 1980 Aspen had the lean burn system, and it certainly had a locking torque converter, and I am 99% certain that it had a lower rear axle ratio, so those are unknown factors in the equation. The Aspen was also significantly 'perkier' than the 1 BBL, even though it was a bit heavier.

Results are going to depend on a lot of factors. Just the rear axle ratio, and the resulting RPM's on the freeway will make a big difference, as that sets the cruise vacuum level and if the power valve in the carb is open while cruising. And, how you drive it and how you tune it up makes a big difference. So without knowing those factors for a given situation, like for Slantsix64's car, you can't draw broad conclusions from one setup.
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That car was designed as a complete package to do what it did. It had an A999 lockup transmission with a low first gear to aid in that perkiness and the lockup converter to help drop highway RPM similar to an overdrive gear. And as you already pointed out, it had the learn burn system.......which it sounds like was operating properly.......however rare. lol

That's the difference here. He is talking about changing the package he has, not completely engineering a new one to give th purpose of economy.

That Aspen and many others like it did get good economy, but it was not because of the two barrel carburetor. It was because of an entire package that was built to provide good economy. With a one barrel on that same setup, it would have gotten even better mileage than it did, but it would have been such a slug that they would not have sold many Aspens. lol.
 
Weber makes a down draft progressive 2 bbl carburetor. The 32/36 DFEV Weber carburetor two barrel progressive carb, electric choke linkage rotates clockwise. Will replace Holley 5200 Models and 32/36 DFAV as well. Redline Weber can answer questions concerning the carb as well as sell the accessories like an air filter unit for it. The Holley was used on some small Fords back in the 80s
 
Well, the other factor in the mileage is how you use it. At a given speed, the power required does not change. The difference there is how the jetting and things like power valve threshold and the mileage can go either way with 1BBL vs 2BBL for a given cruise setting. Put your foot in it all the time, and of course the mileage will go down with more breathing capacity.

Again, drawing broad conclusions from one user experience is not valid.
 
nm9stheham said:
My family had several Darts with /6's, and out of the auto trans cars, my mom's 1980 Aspen with the 2 BBL Super Six got better gas mileage than her 1969 Dart 1 BBL. I understand that the 1980 Aspen had the lean burn system, and it certainly had a locking torque converter, and I am 99% certain that it had a lower rear axle ratio, so those are unknown factors in the equation. The Aspen was also significantly 'perkier' than the 1 BBL, even though it was a bit heavier.

Results are going to depend on a lot of factors. Just the rear axle ratio, and the resulting RPM's on the freeway will make a big difference, as that sets the cruise vacuum level and if the power valve in the carb is open while cruising. And, how you drive it and how you tune it up makes a big difference. So without knowing those factors for a given situation, like for Slantsix64's car, you can't draw broad conclusions from one setup.
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yeah everything is stock 1964 dodge dart 225 rear end with a holly 2bbl
 
you dont find it, you build it. grind the raised 1 bbl faces flat. make a 2 bbl plate. bore out the stock manifold to fit the 2bbl carb plate. use counter sunk screws to hold the plate on.
 
How about a 4bbl with a Holley Economaster 450 CFM 4bbl? weird looking carb to boot.
 
Having ridden shotgun in Max's Commando 67 cuda from LA to San Jose (300 miles?). I can understand why he wants a 2 barrel on the slanty as he cruises at about 80MPH. :D
 
nm9stheham said:
Well, the other factor in the mileage is how you use it. At a given speed, the power required does not change. The difference there is how the jetting and things like power valve threshold and the mileage can go either way with 1BBL vs 2BBL for a given cruise setting. Put your foot in it all the time, and of course the mileage will go down with more breathing capacity.

Again, drawing broad conclusions from one user experience is not valid.
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Oh absolutely. When I was making the comparisons, I was speaking in terms of all other things being equal. Maybe I shouldn't have assumed you knew that. lol
 
KosmicKuda said:
Having ridden shotgun in Max's Commando 67 cuda from LA to San Jose (300 miles?). I can understand why he wants a 2 barrel on the slanty as he cruises at about 80MPH. :D
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That's just keeping up with traffic on the 5.... if you go any slower you're in the right lane with the trucks.

The other week, in the slanty, I kept it to 70 or occasionally 75, But that was on 101 -- I didn't want to torture test it on the Grapevine on a hot afternoon.

It does seem a little lazy on the big hills. I'm guessing it needs a tuneup pretty badly. Definitely taking care of that before I get into exotic stuff -- I've learned my lesson in that department.

What I can't figure out is why it needed 8 quarts of oil to get to LA, and only 1 coming back? I left the cap off on that last fill -- I wonder if that indicates a clogged breather causing excessive blowby? Can't say we noticed any tailpipe smoke.
 
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