A nerd question coming up, get some coffee & eye drops... Perhaps the Doc has performed a few dyno test pulls examining this same scenario.

Josh:
I performed a few calculations to illustrate the percent difference in runner length when a 4 bl. carburetor is mounted with primaries facing forward. The results listed # 1 to # 6 cylinder using nominal lengths in inches including roughly 5" of head passage to the valve seat. The center of the primaries are located approximately 1" ahead of the manifold center line making each runner different length:
# 1=18"---90%
# 2=13"---65%
# 3=11"---55%
# 4=12"---60%
# 5=15"---75%
# 6=20"---100%
Total runner length=89" / 6=14.8"

This set up yields runner lengths varying up to 45%. This has to change the torque output of each cylinder, but by how much? I know that longer runners tend to produce higher torque hence the Hyper Pack manifold which has close to equal runner length for all cylinders.

If one were to turn the carburetor 90 degrees locating the primaries to the left side (west) placing them the greatest distance from the valve seat, and dividing the manifold so that cylinders 1, 2, & 3 run on half the carburetor with one primary & one secondary feeding them, and the same for 4, 5, & 6, the percent difference between runner lengths diminishes to the following:

# 1=18"---100%
# 2=14"---77%
# 3=13"---72%
# 4=13"---72%
# 5=14"---77%
# 6=18"---100%
Total runner length=90" / 6=15.0"

This set up yields runner lengths varying up to 28%, a 17% reduction from the first illustration.

Dose this reduction in percent difference in runner length make for a smother performing engine producing higher torque? My gut is telling me the second set up is the better of the two. But, how much better?

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

After my cam change this will be the next thing I do.

Popcorn

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

The runner length is strictly the length of the tube that connects the valve to the plenum. The carb isn't turned sideways to equalize the distance between the venturis and the valves, but to help equalize wet flow in the manifold by dropping the fuel in a more central location.

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Joshua

Measure the runner lengths from their opening in the plenum to the valve.

The position of the carb barrells doesn't matter for runner length, although it will have some effect on air/fuel distribution......

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

This has been somewhat of a 'philosophical' question on carb orientation in the past on this board.

Mostly the reason for mounting the carb primary toward the radiator has been for linkage purposes. Racers have said they don't notice much in the facing of the carb.

I think coming from the 'street' side of things and looking at how the mix gets motivated toward the valves, it makes more sense to go with the primaries 'out board' toward the drivers side fender, or inboard toward the head....

That being said, with my hyperpack intake I found that primaries toward the head works good, the distance to the head from the bores is closer, and if the secondary plates have to be 'cracked' a bit for idle tuning then that incoming air can sweep any fuel from the primaries into the valves with a bit more 'mix'....

This question kind of is a 'to each their own' type thing. The problem mostly being, we need a 'clear'/plastic intake so we can actually watch what the fuel is really doing when it is cold and puddling, when the vacc. signal is high.... does the liquid fuel tend to run along the outboard walls like a river during typical driving???

-D.Idiot

"Anybody got some of that transparent aluminum from Star Trek so we can do a manifold study????"

I would think the main reason to turn the carb is so that one can install a divider. ( seperate 123 from 456)I don't remember the benefits of the divider, I just remember it was a good thing.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

some are:

1) changes the conditions that reversion in the intake manifold occurs
2) improves mid-range torque
3) separates the carb's tuning into 2 separate "banks" of cylinders

-D.Idiot

I am thinking a divider plate is in order too.

Just wondering if it should be open or partially open on the primary side?

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

An open or partially open divider helps the high rpm, not the low rpm.

So if you have an opening it should be with the secondaries.


Make swappable plates so you can play with it............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Or extendable witha screw that has been modded to be loosened but never removed.

_________________
'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

With any luck the machine shop, rather engine building shop, will call for me to pick up my rebuilt head. This guy is one of these mechanical savants that was breed to make iron go fast. And yup, he is straight six friendly. I will run the divided plenum concept by him and see what his take is on it.

In the mean time I am gathering the necessary bits for a carburetor reorientation.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC