The Holley dual quad secondary balance connection....is it needed?

[427LX]

On the Ford dual quad setups there is that hose that ties both diaphrams together to supposedly let both sets of secondaries open together at same rate for balanced fuel distribution.
Now if that is the case why did Chrysler choose to not use this on their 426 Race Hemi cross ram setup using vacuum secondary 770 Holley carbs. With the cross ram almost acting like two separate plenums and carbs,you would think it would need some balanced action for smooth and even secondary action. Note I have expierence with such a Race Hemi setup back in 1971.
Also on Carter AFB carbs there is no type of balance on factory dual quad setups. Did the Ford engineers discover something on their setups?
Have any of you FE engine builders tried running the Dual quad setup without the connection and noticed any different results on the dyno or at the track?
Does the balanced vac flow tend to slow down the operation of the secondaries?

I'm testing and tuning on my current dual 600 Holley setup on a typical 500 HP 427 Windsor setup and trying things to get best secondary operation just short of a bog condition.
The secondary pots with check ball have a .081 diameter feed hole just under the ball seat. What I have started with is remove the ball and insert a slip in bushing with an .040 diameter hole. This will give me an adjustment location to open up or close up the feed hole.
I recently mounted my GoPro camera under the hood to do a 2nd to 3rd gear test on secondary operation.
This video is of the second test with the weakest secondary springs...the White spring.
Rear end ratio is a 3.50 with a TKO-600 manual trans. RPM at shift point 6000. Car test weight 3000 lbs. with driver.
Both carbs were check for bind free secondary throttle movement and it looks like to me the rear carb might still be a tick behind the front reaching full open on secondary.
Feel free to comment on the secondary action. 
I may try test again without balance connection and later open up my feed hole to a larger size in small steps.

https://youtu.be/tuv8zDdjExM

[e philpott]

No it's not needed , the tube just makes sure the secondary's open at the same time ...... AFB's just have a weighted vacuum door so no way to balance between carbs ..... obviously Chrysler wasn't worried about it , my self I would rather them open at the same time

[cammerfe]

Race applications tend to pay attention only to WOT. Smooth transition is decidedly down the list.

Is a balance tube going to make a massive difference? Probably not---but on the other hand, the designers didn't include it because they didn't have anything else to do on a slow afternoon.

KS

[427LX]

So what did you think of my current secondary function in the video...about right or maybe a bit faster action?

[e philpott]

they for sure open .... hard to tell in the video how close they really are

[FElony]

Seems to me the carb closer to the camera is lagging.

[427LX]

That would be the rear carb. I noticed it too.
Now...if I opened up the hole restriction bushing on that particular carb a bit that should speed it up a bit maybe?

[Falcon67]

Hard to tell but this is some good info, thanks for posting.  I may run a dual 1850 on the dragster after a while.  I will be running the balance connection because I'm bracket racing and anything that makes them work together more consistently will be worth doing.  I especially like the idea of a brass orifice -  more tuneable and consistent than the ball might be.   I prefer to run the purple springs as a start.

I also ran Ed 600 duals on a t-ram on my 302.  They were not tied together and the car was pretty consistent, enough to win two races before the intake gaskets gave out (longer story).  The Eds work well and are pretty easy to tune, but I'd like to try the Thunder AVS with adjustable rate secondaries sometime.  That's a $$$ thing.

[cjshaker]

Maybe it's just me, but after watching it frame by frame, they seem to be pretty even. You're watching the rod on one carb, while watching the lever on the other. Two different things given that the lever works in an arc or circular motion, much like a rocker does. It's like watching a pushrod vs. a valve stem. A good side shot would be more accurate. The hard part would be getting the GoPro mounted solid enough not to vibrate and make the video shaky.

Personally, I think keeping the secondaries tied together is the best route on non-double pumpers and manual cars. It eliminates variables between spring rates and other carb abnormalities.

If you really want to make a difference on how the secondaries are opening/closing during shifts, try not lifting off the gas. The secondaries won't slam shut so they don't have to fully recover and re-open. Since the engine is still maintaining an RPM where the secondary flow is needed, it really is the best way on a manual car for pure performance. Automatics don't have that sudden throttle closing and are able to maintain the secondary opening better.  Just make sure you have a rev limiter or are able to shift pretty quickly.  

Nice job using the GoPro. I've been doing this myself on certain areas of the car to gain some insight as to what's actually happening.

Edit: Ok, after watching that video really closely (the 34 second one), it seems that the rear carbs initial opening is slightly slower, but appears to reach full opening quicker. I think this is where the details really start to kick in and tuning is King. Subtle and small variations all add up, and that's why some guys can spend thousands of dollars on carbs to achieve perfect performance. Flowing every circuit, matching etc. You could try a different spring of the same color and it may change and even up....or get worse...lol

[FElony]

...If you really want to make a difference on how the secondaries are opening/closing during shifts, try not lifting off the gas. The secondaries won't slam shut so they don't have to fully recover and re-open. Since the engine is still maintaining an RPM where the secondary flow is needed, it really is the best way on a manual car for pure performance. Automatics don't have that sudden throttle closing and are able to maintain the secondary opening better.  Just make sure you have a rev limiter or are able to shift pretty quickly.  

Yes. Back when I raced my 289 stick car, I started stutter-shifting, which was my own phrase for barely twitching my right foot during a shift to keep revs where they were. Rev limiters were very much frowned upon in my time and place as suitable only for girly-boys who could not actually drive correctly. This was gospel, no joke. I still have this ingrained in me and I'm going to have to bring back the stutter to retain my manhood.

You could try a different spring of the same color and it may change and even up....or get worse...lol

Swap them and see if the action reverses before diddling with the bushings.