Question for the Mopar Hemi experts...stock Hemi intake?

[427dart]

Always wondered why Chrysler notched the primary bore location of the rear carb location only on the Street Hemi intake.
Any idea?

[F-BIRD'88]

The rear carb is the "primary" carb. With progressive dual quad throttle linkage this is the carb you drive around on most, at part throttle. A big of R/L dual plane sharing.

[427dart]

Yep my thought was maybe a bit more power and better fuel distribution at part throttle. At WOT maybe the flow thru the other secondary bores is to great to make the crossover. Going to try that idea on the primary carb 1 inch spacer on my dual quad setup. I have several spacers laying around.

[numboltz]

IIRC, the carbs were jetted grossly differently [rear only? been a long time...] because of
a fuel distribution issue due to manifold design, and the notch was part of the work-around.
Furthermore, again IIRC, it was an issue at WOT.

[427dart]

Well installed my modified spacer yesterday and took it out for short 2 laps around the block this morning. Right off I noticed the idle bumped up 150 RPM before engine was up to running temp. Seemed smooth the idle a bit and throttle response was stronger and pulled noticeably more with same throttle input. This was on just the front carb primary with no secondary carb input which is typical around town driving. Rear carb starts to come in a 40-45% linkage travel.
When weather clears up better will hook up the A/F reader and see what may have changed. I like it so far!

[tjs44]

So you are using the front carb primarys to feed the whole plenum for street driving?Interesting.Tom

[427dart]

So you are using the front carb primarys to feed the whole plenum for street driving?Interesting.Tom

Yes exactly like Ford did on the FE 427 and Chrysler on the 426 Street Hemi. Just took me 10 yrs to try this little plenum idea

[tjs44]

Thanks,have been running 2-4s since 1963 and always with progressive linkage.I have always believed engineers did thing for a reason and the pontiac SD 2-4 engines came with progressive and used the front 2bbls on the rear carb.I just figured it was because it got the fuel-air pretty close to the center of the intake for better overall fuel distribution.Maybe not?Tom

[Geoff2]

Pretty sure Chrysler used the primaries on the rear carb for street driving. Much better idea because the runner length is more 'equalised' than it would be if the primaries on the front carb are used for driving.

[F-BIRD'88]

On the Fords the holley carbs are mounted facing backwards.. So the back (primary) carb is on the front of the motor.