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PostPosted: Sun Mar 22, 2009 6:20 pm 
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Joined: Sat Feb 16, 2008 1:25 pm
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Location: Downeast Maine
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A nerd question coming up, get some coffee & eye drops... Perhaps the Doc has performed a few dino test pulls examining this same scenario.


[url= & text[/url] showing manifold plenum divider, and Clifford intake.

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 how much? I know that longer the runners, 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 then, 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 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?

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


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