Twin plenum Intake manifold crossover tube

[Kenneth425]

When looking at a twin plenum intake manifold on a Ford V8 with a firing order of 13726548, what is the purpose of a crossover tube between the two plenums effectively coupling them together?
It would seem that isolated plenums without the crosstalk between the plenums would be more effective overall. I have seen examples of the connected plenums on some high horsepower cars. What am I missing? Can someone help explain?
One other question. Would the intake described be able to take advantage of Helmholtz tuning? With the firing order the way it is, it would seem that the oscillations being created from helholtz tuning would be distubed by the overlapping induction cycles. Is this correct or is there still some measure of Helmholtz tuning to be realized?
Thanks in advance for any help!

 

[wgknestrick]

The crossover tube is mainly to equalize pressure between the 2 sides. I doubt that this is absolutely necessary, but many do it just to be safe. If there are other reasons, I do not know of them. I have dual manifolds on my Subaru and I have (in effect) very small crossover tubes to connect to a MAP sensor since my car has ITBs as well.

Without providing any hard data, I really doubt this has much affect on any harmonic tuning of the manifold as long as the tube is small relative to the plenum. The sound has to travel thru this tube for there to be crosstalk, and what little soundwaves make it through this would be insignificant to me.

 

[Marquis]

I used to work for the Ford Group and also did some work on helmholtz tuned resonance manifolding on an uneven (conventional firing) V8.
The balance tube connecting the two equal phases plenums usually has a variable device such as a throttle butterfly.
What you're aiming to do is match the natural frequency of the container- which in this case is the system of plenum and intkae runners to that of pistons (or the air charge within the cylinder) but also allowing for the valve timing.
As the original poster correctly postulated, this works very well on even firing set ups such as V6s and straight sixes, but not so well on conventional cruciform crank V8s. The Porsche 928 S4 uses a twin plenum set up like this- connecting up equal phase cylinders. The twin plenum set up balnace pipe is usually closed- acting as a twin plenum at low speeds, then opens in the mid range only two become a twin plenum again about about 5000 rpm. The work I saw, didnt show that much benefit using a twin plenum over a well designed single plenum. Certainly, the serpentine runner lay out incurred losses- that effect top end performance such that the twin plenum resonance manifold may be more beneficial to low revving truck like applications- where the runner bend losses will have less of an effect.
The resonace "charge boost" effect from the twin plenum lay out on a V8 of this type is only effective over a relatively small rev range.

 

[GregLocock]

Is a conventional crossplane V8 uneven firing? I thought it was even firing intervals but with a weird cylinder order.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Marquis]

As an engine it IS even firing, but when you view just one bank, no matter what firing order you chose on a conventional type V8, there will always be two cylinders close consequetively firing (90 degrees).

 

[Lou Scannon]

And on some earlier V8s, even three cylinders in sequence on one bank (if my source info is correct). I have sighted at least 5 different crossplane V8 firing orders, but I haven't had time yet to how figure out many of these are actually the same due to being reversed or due to non-conventional cylinder numbering.

 

[Lou Scannon]

I take that back about three cylinders in sequence on one bank. That was with the Ford numbering system 15486372
which translates to 12784563 in the conventional system. I will end the hijack here and start a new thread on V8 firing order.