Carb. Mechanical or vacuum secondaries?

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MassDart

MassDart

Lifelong Dart fan
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Trying to decide on what carb to use on my 5.9 Magnum build. I'm thinking 650cfm as it's not a strip car, but more a performance street. My question is, would you use a mechanical secondary set up, or vacuum? Car is 67 Dart. 3:23 suregrip, havent decided yet on the torque converter but thinking it will be 2500-2800 rpm.

Thanks!
 
Spreadbore anything. and I vote a 2800 TC.
cuz I really really liked the way mine launched. (that was 16 years ago).
You ever pull the rope on one of those new Chainsaws, or lawnmowers with easy start? That's what it was like when I nailed it. I could feel the TC tightening up from the instant I gassed it. Then when it got to it's rated stall it just sorta went solid, and when it did, all hell broke loose, lol.
OK wait, that was just a lo-compression 318 with a Thermoquad, lol. But this engine was a dog before the 2800 went in. She ran 3.55s most of the time, but down to 2.76s and up to 4.30s. 3.23s were good, but I really liked the 2.76s. With a manual shift VB, I used to floor it and then upshift as fast as I thought she could take it. This allowed the TQ to sing from a dead stop to 65 mph, sorta stuck at 2800, what a roar, lol.
I used to pull alongside friends at say 30 mph, downshift into First (2800), then nail it, and we'd all enjoy the TQ moan. Oh I almost forgot to mention, she was breathing thru TTIs and dual 3" full-length pipes with Dymomax 3-pass muffs. Otherwise a stock 1973 318LA
 
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If you're looking for any kind of mileage v/s. If you want max power double pumper. Ultimately 650 cfm it's just how you want it delivered and mid range power.
 
I've almost always stuck to the old Mopar Performance advice vacuum secondary for automatic and mechanical secondary for manual and it's worked very well. Although I have run exceptions, like right now I have a 450 vacuum secondary 4 barrel on my slant 6 with a manual transmission, but it runs very well.
 
Vacuum tuned properly delivers excellent performance with decent economy. If you want the power "all in" on launch, then DP is what you want.
 
Ricks70Duster340 said:
Vacuum tuned properly delivers excellent performance with decent economy. If you want the power "all in" on launch, then DP is what you want.
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I think that's an excellent description.
 
Ricks70Duster340 said:
Vacuum tuned properly delivers excellent performance with decent economy. If you want the power "all in" on launch, then DP is what you want.
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A properly tuned double pumper will deliver decent economy and blow the doors off the VS.

Im at a loss as to why people think you can’t tune a DP for performance and fuel efficiency.

It functions like every other carb out there.
 
Rat Bastid said:
A properly tuned double pumper will deliver decent economy and blow the doors off the VS.

Im at a loss as to why people think you can’t tune a DP for performance and fuel efficiency.

It functions like every other carb out there.
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yep. You drive off the front barrels, and they are set up just like a VS front barrels. I don't know why so many attach VS to fuel economy and DP for being race only.
 
best thing about a VS is they are cheaper, and they will run good.
 
318willrun said:
yep. You drive off the front barrels, and they are set up just like a VS front barrels. I don't know why so many attach VS to fuel economy and DP for being race only.
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Cause people get into the secondaries and secondary shooters much more with a double pumper.
I tend to look at rear gear as a hint .2.76s? V.S.! 3.91s? D.p. Torque converter is also obviously a factor. Your 3.23 are a good compromise, you can probably go either way.
 
33IMP said:
Cause people get into the secondaries and secondary shooters much more with a double pumper.
I tend to look at rear gear as a hint .2.76s? V.S.! 3.91s? D.p. Torque converter is also obviously a factor. Your 3.23 are a good compromise, you can probably go either way.
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Just for the record, I had 2.45 gears and a stock converter, no headers, and ran the best ET and 60 ft time with the 750 DP vs the VS
 
318willrun said:
yep. You drive off the front barrels, and they are set up just like a VS front barrels. I don't know why so many attach VS to fuel economy and DP for being race only.
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Not putting DP's in the race only category at all, but common sense dictates the frequent use of the secondaries on a DP WILL reduce economy. The VS carb is an excellent choice for a daily driver.
 
Ricks70Duster340 said:
Not putting DP's in the race only category at all, but common sense dictates the frequent use of the secondaries on a DP WILL reduce economy. The VS carb is an excellent choice for a daily driver.
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DP only uses more gas if you floor it. Driving daily without flooring it, it won't use any more gas but I won't argue it :)
 
Ricks70Duster340 said:
And frequently using the secondaries is my point exactly regarding fuel economy with the DP.
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If you are putting your foot into the secondaries all the time why are you concerned with fuel economy?

It takes .45 pounds of fuel per horsepower per hour.

So the more power you make, the more fuel you will burn. It’s simple math.
 
Ricks70Duster340 said:
And frequently using the secondaries is my point exactly regarding fuel economy with the DP.
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My thought is if somebody is conserving fuel, then they are not flooring it. Like going back and forth to work per say. The DP will do all as well on the front primaries as the VS. IF a guy is hot rodding, flooring it, burning tires, then gas mileage is NOT on his mind so the DP will give better performance and mpg is not a concern during these activities
 
The one big thing (no pun intended, "big") is that they MUST be sized more carefully. A 650 on a 5.9? You are way under the "large" end
 
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