4 bbl vs 6 pack

[Andrew]

Building a 440 .50 over, solid flat .550 lift cam, eddie rpm heads. I have a 6 pack set up and a demon 750 4bbl w/ Holley street dom intake at my disposal. I would rather use te 6 pack set for nostalgia purposes but would go 4bbl if the performance gains would be worth it. Any suggestions?

 

[696pack]

The right intake and 4 barrel Dominator WILL out perform a factory six pack set up. However the difference in the "seat of your pants" may not be noticable on the street but will show up in your clocked 1/4 mile time.

Most people would much rather have the six pack "cool" factor.

 

[dantrap]

If the 6 pak is fresh i would use it. It will work fine on a street machine and they are cool. I have seen test data showing a little additional power with the 6 pack and i seen the opposite. Its all in what you like, they both will work fine. good luck

 

[daredevil]

that 750 might be a little small. dont 6pks add up to 950 cfm?
?

 

[Deleted member 214]

350 cfm center carb, 500 cfm each outboard carb, total of 1,350 cfm by factory specs. I read somewhere that 2-bbls are rated different than 4-bbls, so apples to apples the six pack would not flow as much as two 675 cfm four barrels. I would bet that it would flow more than a single 750, though!

 

[Meep-Meep]

Yes, the 500 CFM two barrel = 354 CFM in 4 BBL ratings. Just take the 2 BBL CFM and divide by 1.41. You also have to consider the six pack intake is a divided plenum, which kind of fools the engine. Only half the barrels are exposed to 4 cylinders thus giving a more favorable pressure signal to the carbs. Same philosophy as the 750 - 800 CFM TQ on a smogged out small block with single exhaust. Two totally different concepts on intakes here.

 

[69HEMICORONETR/TCONV]

I would go with the 4bbl for performance gains.

 

[Deleted member 214]

OK, so 1,350 cfm divided by 1.41 means 957 cfm, or Holley Dominator territory. I'll keep my two-barrel motor...

 

[63RedFury]

I had a real 69 1/2 Road Runner about 6 years ago,and there is nothing like 3 carbs.Lot of fun........

 

[macdiesel]

Go 6 pack! You'll have more fun on the street and it ain't too shabby for the strip. The 2bbls will be much more responsive. My buddy has the same set up in his cuda and it'll pull you into the back seat.

If the Demon is a Race Demon don't think of it like a 750. Its closer to a 950, so you might be over carbing for the street.

 

[69 Runner]

Having run six packs I can attest to the WOW factor from the looks, and the OH MY GOD factor when the outboards open up. Ain't nuthin like it. They are fairly easy to tune (and NO PROBLEM to KEEP tuned) when running them with a (close to) stock cam. All that said it would probably be easier to tune a big 4V with a monster lumpy cam than the Six Pack.

If it were me, I'd do whatever necessary to run the Six Pack.

 

[moparstuart]

i have had great luck with my six pac , and if i decide to go on a road trip to a car show , if i drive reasonable and try to stay out of the out boards , i get 18 miles to the gallon off that center 2 barrel .

 

[moparstuart]

I also have the demon six shooter set up on my daytona clone , those babys are huge and there is no gas savings , but man they scream

 

[macdiesel]

That Demon 6 pack is pretty. I'm the only guy in my club that has a 440 and no 6 pack. While my Torker and 850 DP are fun enough, I wish I had one.

 

[69 Runner]

my (ex) Challenger

 

[Andrew]

Do you guys think I will run into vacuum issues with a 550 lift mech cam? (Manual brakes)

 

[Deleted member 214]

Six pack

It's only a two-barrel motor... :grin:

 

[Andrew]

I was under the impression that running a large cam would decreaese the vacuum required to open the outboard carbs.

 

[dantrap]

Andrew, i used a 6-pak with the old DC .590 cam without any problems. Sometime i think we over think ourselves. There is a lot of published build ups you can track down to help ya make the choice.

 

[macdiesel]

The vacuum canisters run off of carb vacuum or lack there of, not manifold vacuum. As for your power brakes, thats another story.