six barrel vs four barrel

[TRAMO]

would like to get some thoughts on 4 and 6 barrel carbs.as i understand it the only difference in a 440hp and a 440hp with six barrel/pack is about 600cfm in the carbueration.cam,exhaust, and heads are same.how does the six barrels make so much more get-up and go. also how much improvment would a 383hp with six barrels since the 383hp has same exhaust,cam and heads as 440+6?

 

[lewtot184]

the stock iron 4bbl intake doesn't flow a lot of air, maybe 200cfm(?). the 6-pak intake will flow around 290cfm. this is significant; especially when more air flow capacity is added thru the carbs. as a comparision when a stock 4bbl 440 i have was upgraded to a 6-pak there was a 6 tenths reduction in 1/4 mile e.t, and eventually ended up being a 9 tenths reduction and 8+ mph gain with a little fiddling around. i ran a dp6b intake and carbs on a 383 4spd road runner back in the day. the 440 carbs are a little large but worked fine. corvette carbs work real good but aren't as easy to hook up.

 

[super-bee_ski]

Actually,
The 6-pack (6-BBL) engine is internally different too.
It has different connecting rods and connecting rod bolts, different Harmonic Balancer, balanced differently.

But, many have simply put a 6 BBL induction system on a conventional 440 Magnum.

I have a brand new set up in the box.

383 MOD?
Nope, I personally would not "six-pack" a 383.

But, it would look sweet!

 

[tallhair]

Budnicks is probably the resident expert on 6 BBL intakes on 383's

 

[super-bee_ski]

Budnick, Budnicks, anyone......?

 

[lewtot184]

Actually,
The 6-pack (6-BBL) engine is internally different too.
It has different connecting rods and connecting rod bolts, different Harmonic Balancer, balanced differently.

But, many have simply put a 6 BBL induction system on a conventional 440 Magnum.

I have a brand new set up in the box.

383 MOD?
Nope, I personally would not "six-pack" a 383.

But, it would look sweet!

the '69 a-12 short block had the same pistons, rods, crank, balancer as the 4bbl. the heads differed with street hemi valve springs and chrome stem valves. '69 & '70-'71 had the same cams, timing chains, and heads. '70-'71 had the 10.5:1 pistons, heavy rods and were externally balance. some early '70's had an alum intake.

- - - Updated - - -

i did a lot of playing around with a 383 6bbl between 1970-1973. tried the factory vacuum carbs, corvette tri-power carbs and the aftermarket mechanicals.

 

[Meep-Meep]

First of all Holley 2 BBL's are rated differently than 4 BBL's. For example and 500 CFM 2 BBL in 4 BBL thinking = 354 CFM. 4 BBL and 2 BBL are rated at different pressure drops so the numbers change accordingly. Also the 6 BBL intake is a divided plenum dual plane and that helps to create a stronger signal for all that venturi area. If you want something that will work well with minimal tuning use a 4 BBL. The 6 BBL is not 100% the best thing you can do. It looks cool as heck, and can work great, but only if you spend a lot of time tuning it.

In my own experience on a very mild 440 (see my post under the 12 second build thread) I ran high 12's with a factory iron intake and a 750 AFB. Hardly a slouch, but I also agree there is room for improvement. On this same engine I installed a 6 BBL and I have yet to make it equal the performance of the single 4 BBL. The 6 BBL is now on my 69 RR and I expect to spend a bunch more time tuning to get the fuel curve correct.

 

[kelly]

what are you asking for it f you sold it?
thanks

 

[super-bee_ski]

Uh,
I think the 6-Pack Rods are different....
For one thing, they are HEAVY.

 

[moparcanuck]

The 69 1/2 Six Pack short block was the same as the 4bbl. Changes were made in the 70 production year.

I put a Six Pack on my 69 GTX just because it looks cool. :hello2:

 

[Propwash]

Big questions should be; How much do you want to blow, and how much do you want to tinker with your carb(s). Performance wise you can make a 4BBL combo perform the same as a 6BBL combo for less money. 6BBL's at the car show will get you a lot of ewww's and ahhh's and a big air cleaner. Definitely win's the bling factor hands down.

 

[440+6]

Here is how you do the conversion between 2bbl and 4bbl carbs

4 bbl carbs are measured at 1.5hg of vacuum and 2 bbls at 3hg of vacuum

To convert from one system to another (with a very small percentage of error) is simple.
Simply use the square root of 2 (1.414).
So to convert a two-barrel rating into a four-barrel rating, divide the two-barrel rating by 1.414.
To convert the four-barrel rating to a two-barrel rating, multiply the four-barrel rating by 1.414.

A six pack setup claimes 1350 cfm but it's actually around 955 cfm if you convert to the way 4 barrels are flowed.

In case anyone cares

 

[lewtot184]

Uh,
I think the 6-Pack Rods are different....
For one thing, they are HEAVY.

'70 and '71 are heavy rod externally balanced engines. '69's used the standard rod and were internally balanced.

 

[super-bee_ski]

Big questions should be; How much do you want to blow, and how much do you want to tinker with your carb(s). Performance wise you can make a 4BBL combo perform the same as a 6BBL combo for less money. 6BBL's at the car show will get you a lot of ewww's and ahhh's and a big air cleaner. Definitely win's the bling factor hands down.

This all goes back to what i was saying earlier this week...
These cars were a bit on the "maintenance heavy" side.

 

[Propwash]

This all goes back to what i was saying earlier this week...
These cars were a bit on the "maintenance heavy" side.

LOL...I agree.

 

[lewtot184]

the only real problem i've had with 6-pak carbs is getting the idle circuts where"i" want them. this is typical of any carb that has the emissions built into them. the only real issue with the carbs is lean idle and main metering in the center carb. i've had 4 sets and have found sets (i never mismatched carbs) were more finicky on the idle circuts. never had any kind of WOT opening issues. i never try to re-engineer them; they are what they are. another thing is they want fuel! typically the 2 valve mech pumps won't come close to feeding them. i modify 3 valve pumps. i prefer not to use electrics for my street cars due to reliability issues. i've always been dismayed at the "nay-sayers" who've never owned one, never worked on one, hell probably never drove one least wise rode in one.

 

[Meep-Meep]

the only real problem i've had with 6-pak carbs is getting the idle circuts where"i" want them. this is typical of any carb that has the emissions built into them. the only real issue with the carbs is lean idle and main metering in the center carb. i've had 4 sets and have found sets (i never mismatched carbs) were more finicky on the idle circuts. never had any kind of WOT opening issues. i never try to re-engineer them; they are what they are. another thing is they want fuel! typically the 2 valve mech pumps won't come close to feeding them. i modify 3 valve pumps. i prefer not to use electrics for my street cars due to reliability issues. i've always been dismayed at the "nay-sayers" who've never owned one, never worked on one, hell probably never drove one least wise rode in one.

My problem when I had the 6 BBL on the 440 auto Belvedere was getting it to lean out on tip in and cruise. I can get the idle OK but as soon as you take off under light throttle conditions it's rich (12.5:1 AFR). I'd like 14.5 or even pushing 15:1 on cruise. Hammer it and it starts to correct itself towards lean. Now that the system has been transplanted onto the 69 RR I'll be revisiting it when I get that car running.

 

[tallhair]

My problem when I had the 6 BBL on the 440 auto Belvedere was getting it to lean out on tip in and cruise. I can get the idle OK but as soon as you take off under light throttle conditions it's rich (12.5:1 AFR). I'd like 14.5 or even pushing 15:1 on cruise. Hammer it and it starts to correct itself towards lean. Now that the system has been transplanted onto the 69 RR I'll be revisiting it when I get that car running.

And I'll be picking your brain brother

 

[biomedtechguy]

I have a 70 V code Roadrunner with a 71 440 and the Edelbrock aluminum 6 bbl intake. I have tweaked it by tuning only and changed the center jets from 62s to 65s and it is amazing with room for more improvement I'm sure. I love it, and even when I build a stroker RB for it, the 6 bbl is a MUST afaic. I have also seen numerous back to back dyno comparisons on built 5xx to 6xx HP motors and the 6 bbl compares favorably with a modern race 4 bbl and intake.

 

[68 HEMI GTS]

my 6 pack with a 500cfm center is pretty comparable to a tm6, 1" spacer, and a 1050/4150 anular carb. Both times out were decent air, through mufflers, Dot tires, and driving to the track. Haven't played with timing or jetting at the track yet.

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