question for hotrod/muscle car experts

obrut · 09-27-2006, 07:51 PM

whilst i love early 911s in particular, i get a kick out of most modded cars.

before a long flight, i recently bought a book on muscle cars (MUSCLE) and hotrods (HOTROD MILESTONES) - both excellent by the way - to learn a little about these types of cars.

my questions is how do "6 pack" carb setups (ie. 3 sets of 2 barrel carbs) work with V8s?

with 6 carb barrels and 8 inlet tracts - how is flow to each inlet tract equalized? does it go into a common plenum or am i missing something?

fintstone · fintstone's Garage

It is all in the manifold. Look at the photos of these and it will be obvious:

http://www.gerlecreek.com/documents/tptechnical.htm

CS119laCoS · 09-27-2006, 08:03 PM

Quote:

Originally posted by obrut
does it go into a common plenum ?

yes.

kmhemi · 09-27-2006, 08:11 PM

I've got a 70 Challenger RT with the original 426 Hemi and 4 speed. The 426 came from the factory with two four barrel carburetors. They are pretty touchy to keep in tune. Mine also has a solid roller cam which adds to the joy of tuning.

pwd72s · 09-27-2006, 08:34 PM

My tri-power Goat (GTO) was easy to tune...progressive linkage, so the car ran on the center carb until you hit the loud pedal. Then the other two would kick in. The lingo of the day: "six pack" was MOPAR..."tri power" was GM. I'm doing a bit of guessing now...if memory serves, when all three of my carbs were open, the flow was around 1400 cfm? Today, a single 4 barrel and single plane manifold will produce more power due to design advances in both carbs and manifolds. But, ohhh the harmonics of a multi carb set-up at full tilt boogie! It was glorious!

If I'm not mistaken, nostalgia buffs can now find triple carb manifolds new.

pwd72s · 09-27-2006, 08:38 PM

Quote:

Originally posted by kmhemi
I've got a 70 Challenger RT with the original 426 Hemi and 4 speed. The 426 came from the factory with two four barrel carburetors. They are pretty touchy to keep in tune. Mine also has a solid roller cam which adds to the joy of tuning.

Ahhh, yes...that was the rep back in the day. That Hemis were difficult to keep in tune. But when in tune? The master of the midnight drags. My Goat was a Hemi victim. The sneaky dude had a 383 emblem on his fenders. No fair!

kmhemi · 09:09 PM

I think Mopar's old six pack setups were 1200 cfm. I think the center carb was 500 then the two vac. operated aboutboards were 350 cfm each.

obrut · 09-27-2006, 09:42 PM

thanks guys

RANDY P · RANDY P's Garage

Common plenum -ancient technology from an era when large carbs were thought to be sure power. A PITA to sync and tune.

Damn right a single 4 barrel and a modern single plenum will kick the crap out of it. You can run 8 second 1/4 mile ET's these days with that combo..

rjp

fintstone · fintstone's Garage

But multiple carbs get lots of cool points...like MFI.

techweenie · techweenie's Garage

When I first got into 911s, I saw a manifold some guy welded up with a plenum box in the middle and an American 4-bbl carb. It can be done, but it's a weird choice for an engine that had a near-perfect setup to start with: overhead cam, hemi-head, one carb throat per cylinder...

asphaltgambler · 09-28-2006, 05:30 AM

Back in the day multiple cvarb set ups were the next increment in HP increase. Typically though the carbs were small cfm even the early 2X4bbls were only 400-450cfm each.

Most would make slightly more HP but the torque suffered through-out the mid range. Biggest issue is that the intake manifold runners are too short on these set-ups resulting in poor fuel distribution.

But that was the current technology then.

pwd72s · 09-28-2006, 07:07 AM

Quote:

Originally posted by fintstone
But multiple carbs get lots of cool points...like MFI.

+1! Guess I should consider myself fortunate, I had the tri-power, now have MFI.

kmhemi · 09-28-2006, 07:16 AM

The Hemi came with 2 625 cfm Carter AFB's

Carbs are ok but I will admit injection is the way to go. I love my 911 and I plan on doing everything I can to avoid going to carbs.

obrut · 09-29-2006, 12:22 AM

just to be clear - i never suggested fitting six pack carbs to a 911, i merely wished to understand how 6 barrels evenly fed the 8 inlet ports of a V8.

i too am a big MFI fan (as you may expect having 3 MFI cars...)

asphaltgambler · 09-29-2006, 05:42 AM

The answer is not very evenly

BeyGon · 09-29-2006, 05:52 AM

One of my cars is a 71 Skylark with a 455, 800cfm carb, it is for sale, if you want a car that will run in the 13 s and look good for not a lot of money, this is it.

sammyg2 · 09-29-2006, 10:02 AM

I ran 660 center squirters on my hemi, never had much problem keeping it in tune except for that one time I back-fired the supercharger, took a while to grow the hair back..............

pwd72s · 10:11 AM

Quote:

Originally posted by kmhemi
The Hemi came with 2 625 cfm Carter AFB's

Carbs are ok but I will admit injection is the way to go. I love my 911 and I plan on doing everything I can to avoid going to carbs.

My '77 Dodge power wagon is running a single 625 AFB atop an edelbrock "performer" dual plane manifold. Found a twin snorkle air cleaner off a '70 Challenger. 360, running Keith Black hypereutectic pistons, heads flowed by a local machine shop used by the dirt track racers, Comp RV cam...other goodies. Built for 4X4 torque...works pretty well. Even a single 625 AFB has no trouble drinking a lot of dead dinosaurs.