exhaust systems

[redrider]

Can of worms. The Mille and Sport do not have linked head pipes but the V11 does. The mille with the H collector and the other two with the siamesed type collectors. So why use the linked headers? Noise suppression? Is power enhanced by using them? I suppose the real question may be has any one actually compared the linked to non-linked headers on the dyno. I have read several engineering papers on the subject of exhaust tuning but none addressed the subject. Any exhaust tuners here?

[Hymes Inc.]

I was having this coversation with Ron from R&K cycle. He showed me a triumph twin that had the headers linked a few inches from the block. He said that was supposed to be the best place, as close to the block as possible. Couldn't tell me why but he has much wisdom so I believe him.

[swooshdave]

The LeMans 850 had a crossover near the heads and it made 800 hp. What's to question?   

[travelingbyguzzi]

My feeble understanding is that  close to the head enhances the top end and the hpipe collector enhances low end torque. This seems to make sense since the 'sport' bikes have thwarting crossover near thwarting head.
I think for a year or two some EVs  had the crossover near the head.

[jlburgess]

I think it has to do with backpressure to effectively tune the wavelength of exiting exhaust gas.  It seems unlikely that aftermarket manufacturers have the ability to tune this to the nth degree.  Minor details.   If the stock pipes were not so heavy they probably wouldn't sell any.  I know I'm pretty tired of Harley clowns whacking open the throttle with straight pipes in front of my house and setting off car alarms.  Fags!  SPC.

[redrider]

Judging by the responses and my own net searches, it seems no one can explain with hard data why linked head pipes are used. My one printed document is from a Norton performance set up that flatly states "do not use the linked head pipes. Their sole purpose is noise suppression. They will reduce power." Looking at F1 headers-no linkage. Even the ones I installed on my F series were not linked. The early V11's were not. Likewise with the Mille and Sport. If multi cylinder engines are just a collection of singles, what good is it to link the headers? I understand the flow scavenging effect of the collector system but to have a hole perpendicular to the flow path seems a travesty to all that is holy.

[Two Checks]

A X-over uses the exhaust pulses to allow each cylinder to use both mufflers, creating a scavenging effect. Placement of the x-over affect where the power is made, low, mid or high rpm.
Chrysler used the same principle in the early 60s with the cross ram big blocks. They had dual quads with the carbs sitting outboard of the valve covers with the L carb feeding the right bank and vice versa. They found the internal length of the individual runners affectedwhere it made best power.
It wasa ram air effect and it's from where thedrag racers, the Ramchargers took their name.

[redrider]

Tuned length intakes and exhaust tubing I understand. The "Balance Pipe" is what links the headers before the collector. Allowing the engine cylinders to share a muffler smacks of noise abatement first with actual power as a casualty. Blending and scavenging occurs at the collector. Example, my Benelli triple. 120 degree with balance tubes on the headers. Number one fires and the ex valve opens. Gasses enter the head pipe and are immediately allowed to travel down the header and into the other head pipes as well, decreasing pressure. What about the reflected wave? Would it also be diminished by the balance pipe? Numbers 2 and 3 have their own gasses to deal with. Any back to back dyno runs with and without balance pipes data out there?

[Two Checks]

The balance tubes have nothing to do with EPA. It's been used for decades for better hp and torque.

[Rough Edge racing]

  On the Lemans 1 I had there where two crossover pipes if I remember correctly... I replaced the stock exhaust with no cross over pipes and Conti mufflers.....No difference in part throttle performance but the top end seemed slightly better... probably because I reved it more to hear the Conti's

[Triple Jim]

When I ran the specifics of my Mille on an online exhaust system calculator that was made to design head pipes, it came up with almost exactly the dimensions of the Mille system from the heads to the rear crossover.  I then understood why the crossover was there.  It effectively causes a sudden pressure drop (exhaust can suddenly take 2 paths), creating the desirable negative return (scavenging) wave at the correct time.

A crossover near the heads has to be for noise reduction (twice as many pulses that are each half as big at the muffler exits), and/or to partially detune the system to smooth out peaks and valleys in the torque curve that are undesirable.  Since the rear crossover has similar noise reducing qualities, I believe the front crossovers are mostly there to help make a broad, smooth powerband instead of a one with peaks and valleys.

Some of the Suzuki 2-stroke 3-cylinder 750s (GT750) had a tube that connected all three head pipes, and this was purely to smooth out the powerband so the touring motorcycle wasn't wild and peaky like the Kawasaki H2.

[rocker59]

The rumor on the V11 Sport/LeMans with front crossover was "improved mid-range".

The truth in multiple dyno runs from multiple bikes, with and without the crossover, says the difference is negligible to nominal.

[Rough Edge racing]

  A cross over pipe will also reduce or eliminate a flat spot or reversion problem that usually occurs around 3500 rpm on highly tuned two valve engines...

[ritratto]

I have a '03 LeMans and the headpipe cracked at the crossover, so I bought some earlier ones with no front cross over from Moto Guzzi Classics and installed. No dif that I can tell and I ride in every type of condition and speeds.  So, forgetaboutit!

[redrider]

Thanks to All. I am sifting through the web results. I like numbers.

[rocker59]

Thanks to All. I am sifting through the web results. I like numbers.

You may find some specific posts on this subject over at the v11lemans.com forum.

As I recall, Todd@GuzziTech ran some dyno runs with the stock systems and his "crack proof" headers, reporting no real measurable difference with and without the front crossover.

[oldbike54]

 Maybe the best reason for running a crossover is that ir allows for smaller mufflers because both cylinders share each muffler . As for where the crossover is located , seriously don't think that makes any real difference .

 Dusty

[rocker59]

1 crossover good.

2 crossovers, not really necessary,  but were fashionable for awhile.