Long Rams 3.0

One more thing, what purpose does the balance Tube actually serve?
Is it for idle quality, to help "balance" the carbs someway for some purpose, it a "softener" for intake pulses to help the carb, does air flow much in the tube, can it be replaced by a #12AN hose, etc?
My thinking, for an EFI sequential port injection Long ram, it ain't needed.
Well?

You'll find your answer in these wise words my friend

Must See video

Come on give some advise they will help him out:

https://m.youtube.com/watch?v=Wq6hVs6K5mc

It might be worth studying intake manifolds with long runners that were designed by Chrysler afterwards.

The iron V10 truck engine manifold has 25 inch runners with EFI.
The “plenum” volume of this manifold is far larger than the Long Ram.
This probably works far better than the balance tube.

The Magnum V8 “beer barrel” manifold has 15.5 inch runners and a HUGE plenum volume.

My memory is a bit fuzzy but one of the college textbooks on Internal Combustion Engines has several pages on a long runner intake manifold that Jaguar designed in the 1970s with example mathematical equations filled out on how to size the runner cross section and the cubic inches of the plenum.

The $140 software program Engine Analyser 3.0 from Performance Trends has the ability to analyse more than a dozen intake manifold designs and asks you for runner dimensions and plenum volumes.

Not in a long horn cross ram application it won't.

I have a vague recollection of a rule of thumb that says plenum volume need to equal no less than one cylinder's displacement on a multi cylinder engine. But that's probably out of date.

http://utawesomeperformance.com/kegger-vrp.html

Worth a read and notice the software.

Plenum volume on an EFI application is not super critical like it is in a carb application because you're not worried about providing the right vacuum signal to the carb. You can go bigger on the plenum on an efi build and not hurt anything.

The balance tube on the cross ram would be to help balance out vacuum signal to the carbs. Imagine at part throttle in a low/medium vacuum situation, the vacuum signal off 4 alternating cylinders instead of 8 will be more uneven. Distributor vacuum advance and pcv wouldn't oppose a more stable vacuum signal either! If the carbs weren't properly sync'd, I guess the balance tubes could help bandaid this as well.

If you're using a speed density EFI system, the balance tube would help provide a more stable MAP signal to the computer in much the same manner. You could downsize the tube size in an EFI application, however I would probably just leave it.

As for the intake runner length, rumor has it chrysler used a formula of 84000/runner length in inches = peak rpm of power boost. There's various calculators out there that use the speed of sound vs runner length to calculate harmonics, peak rpm ranges, etc. The ones I've tried do put the chrysler figure in the same ballpark.

Thank you for the serious replies.
My consensus at this point is:
1. increasing the size of my separated LR plenums would have little downside, unfortunately there is no easy solution for that because of space and headers.
2. OEM LR plenums are rather anemic sized, Since I am going to EFI throttle bodies, I have room to add a 1-1.5" open spacer, or at least experiment with that potential solution.
3. Hadn't considered the ignition vacuum signal issue , I might be able to just plumb the signal line to both of the small OEM plenums for a summation signal?. Not sure how much smoothing takes place in the vacuum sensor or software to reduce pulsing..
4. I'm inclined to remove the remove/eliminate the OEM crossover, doesn't seem yet as a bad move, but does have some risk/uncertainty in the outcome.

Really digging deep into the cobwebs here, but I also recall that without a balance tube a V8 will tend to run like 2 four cylinders rather than one V8. But I'll be danged if I remember where I saw that. Probably some patent application.

I would just keep the balance tube. The connections are already cast into the intake and the middle of the tube would make a nice place to tie in your MAP sensor. Plus it looks good!



Interesting read, however it seems he cherry picks his data. Other builds I have seen on the internet have had guys trim down the ends of their intake runners to smooth out airflow going into the runners. I suspect that's the effect that his plenum reducing plates are having. If so, that's a better solution than shortening the runners to radius in the air flow easier.

I would also keep the balance tube. In our V8s, the cranks are all cross plane cranks. That is, the throws for the rods are each 90 degrees out. Versus a flat plane crank where throws are 180 degrees apart. What this does is add uneven firing to the cylinders. But does make for a smoother running engine. This uneven firing will "communicate" the air pulses back into the manifold. It really shouldn't matter too much with long tube but it is possible that the balance tube will help dampen the uneven pulses some.

Just my

I would like a scientific explanation as to why the 1992-1995 version of the Magnum V8 intake manifold had a center divider cast in place that reached down within 1/2 inch of the bottom.

Was it there to block reversion pulses?

Was it there to more evenly distribute EGR?

A year after EGR was eliminated in 1996,
the 1997+ plus intake castings had the divider greatly reduced so that there was 4 inches of open area above the bottom.

In 1998 a new camshaft was introduced and peak HP at 4000 rpm went up by 15

I wish in 1998 that Chrysler had taken the science of V10 intake manifold and createda V8 version with 25 inch runners that would have peak torque as low as 1200 rpm resonate at both 1700 rpm and 3300 rpm. Magnesium and no troublesome plenum plate or gasket.

Sample quote
A Helmholtz resonator intake manifold was tuned to boost torque at 1700 and 3300 rpm. Long primary runners curved over the right cylinder bank to clear the hood. Resonance in the 25-inch primary runners enhanced low speed torque, with peak torque as low as 1200 rpm. Two plenum chambers supplied air to five runners each. Plenum chamber volume was tuned to resonate at 3300 rpm, broadening the torque curve. Passages across the longitudinal center of the manifold fed air from the throttle body to the plenum chambers.
End quote

https://www.allpar.com/mopar/V10.html

https://www.allpar.com/mopar/performance/manifolds.html

i'm also using the long rams in my 33 dodge humpback panel truck, so i already know "they won't work". my plan is basically the same as the OP. as i can go up [no hood], i'm planing 2" spacer/adapters for the manifolds to throttle bodies, plus cutting [from the undersides] the dividers out, making them short rams. also keeping the divider and using it for the map sensor. i'm also considering fabbing plates to position the injectors at the head ports, but at this time, not put much thought into that deal.
continue on please.

I wonder if it was there to help radius the air into the runners? Might have also served as enough of a restriction for flow through both bores of the TB that eliminating the divider was a wash in terms of power production.

Seriously though. How may engines have you seen that don’t draw all intake air from the same plenum?
Hilborn mechanical injection with 8 stacks is one.
How about those 1970’s British Cars, what did they have?
1950’s 6 carb setups had balance tubes.

I have a Long Ram car and have driven it 22K miles. You can purposely mis adjust the carb openings and it still runs And drives. Of course it runs way better with the carbs synced. I can’t see it working worth a darn without the balance tube. Chrysler called it a “balance tube” for a good reason.

I can't dispute your findings, but the contention to me is, does using EFI and losing the carbs make the "balance tube" superfluous?
As much as i want to cut it out, I'm likely to leave it initially, then bypass it ,and then make a determination, more work, but a lot less risky if i choose wrong.
Was hoping to find some sound reasoning first.

I love that site and recommend it often!

FWIW, if you're using a speed density EFI system, it's recommended to have all the cylinders tied together one way or another. The guys who are doing speed density EFI systems with Hilborn or other type individual throttle bodies generally still tie all the cylinders together, even with something small like a 1/2" hose in order to get a decent MAP reading. I guess if you were using an EFI system that used a mass air flow sensor instead of a map sensor you could get away without it.

Well, using a MAF would tie them to a common point as well, the MAF sensor does need to measure all the air flow.

Getting a 8 cylinder “balanced” reading for a single MAP sensor is hard to begin with, and would seem especially hard for the old style Long Ram design.

A EFI that has software that has individual “tweaks” for each of the 8 cylinders might overcome many limitations if it allowed adjusting BOTH fuel injector flow and ignition timing.

600 rpm, 1600 rpm and 4000 rpm behavior at each cylinder might be WAY DIFFERENT with the old Long Rams.
Modern state of the art intake V8 manifolds vary 8% per cylinder according to the Bosch Automotive Hankbook.

lots of interesting points tossed back and forth here. keep it up please.

We/I were discussing the long rams rather small plenums. Not sure I mentioned it here on this post, but I'm planning on DIY converting the more common 30" LR to the rare 15" style. Which really just means taking 2 Siamesed runners and making them one for approx 15"just past the throttle body. So does that somewhat increase/boost plenum tuning/volume, even though its located in two separate runners per LR?

Still contemplating all the balance tube considerations.

This was an original long ram car,changed the cam to I don't even remember,for a 4000 lb. car ran much better than I expected back in the day.Also,personally I wouldn't consider without the balance tube.

yes but you could do that before the throttle bodies so your tie in point could be complete separate from your intake manifold. Alternatively I wonder if you could put a MAF on just one cylinder and tune assuming equal air/fuel flow to all cylinders.