About crossover

[Mechano]

Hi there!

I want to ask something about the importance of the crossover tube on Harleys and big twins.

It's long time I see crossovers on every bike's engine with more than one cylinder. Everybody know the reasons why they esist and are used on both stock and racing exhausts.

Some days ago I had a strange conversation with an italian exhaust maker. I asked if they have built a variable sonority exhaust for new '04-'05 Sportsters. He told me yes
So I asked details like if they where bolt on systems and used the stock brackets or their own brackets.

The person told me they have their own brackets and don't have crossovers.
He told me the crossover is not necessary on an open exhaust. In fact it's useful with closed pipes so the exhaust can go out from two ways, helping the mid and hi-end torque and power.

But I was sure that eliminating the crossovers there're some minor problems like more vibrations and some flat spots or minor inefficiences. And both people and exhausts producers where in accord to renounce to the crossovers only for a better look and/or minor engineering and building problems that a crossover brings on a v-twin engine schema.

When I used to build my own exhausts for racing japs I always used to calculate the right diameter and position for crossovers, and had always better performance using them than not...

Now it sounds strange to my hears, that without crossovers it's better.

Someone with more experience on big twins can explain me?
Do you have experience of better or worse performance with or without crossovers?

--
Mr. Mechano
Kawasaki ZRX1200 152hp
Soon (next week) '04 XL1200C red/silver

[gwcrim]

I think the power difference is pretty minor, though it would exist. But the sound and vibration are both more evident without a crossover. That I know for sure.

[alleydude]

...on Harleys and big twins.

Well put! :laugh

[Mechano]

Well put! :laugh

What does it means?

I consider big twin every engine with more than 1 liter displacement and two cylinders... Including all the metric cruisers.

--
Mr. Mechano

[CuL8R]

What does it means?

I consider big twin every engine with more than 1 liter displacement and two cylinders... Including all the metric cruisers.

--
Mr. Mechano

Boy, are you wrong!

BTs are all Harleys that are not Sportsters.

[sportsterrific]

Hey Mechano, I see you're from Italy so maybe your terminology is a bit off. Here in North America, we have Metric cruisers, and Harleys. Harleys are basically divided into the Big Twins (BT) and the Sportsters. Sporsters are the best of the bunch.
The crossover has to do with managing exhaust pulse waves and resonance. I don't know what they do for power delivery, but I suspect that they are mostly eliminated for looks, and weight reduction, which to me would offset the benefits of having a crossover.

[Mechano]

Hey Mechano, I see you're from Italy so maybe your terminology is a bit off. Here in North America, we have Metric cruisers, and Harleys. Harleys are basically divided into the Big Twins (BT) and the Sportsters. Sporsters are the best of the bunch.
The crossover has to do with managing exhaust pulse waves and resonance. I don't know what they do for power delivery, but I suspect that they are mostly eliminated for looks, and weight reduction, which to me would offset the benefits of having a crossover.

Yeah, maybe there's a bit of difference in culture, terminology and traditions.
When you put your fingers to imitate cow horns, in Texas means good luck, in Italy (or into italian-american community in your country) you are talking about a man who had his wife go with another man. And if you point it against someone you don't know, maybe (surely) you'll know lot of problems, expecially in the south of Italy and Sicily in particular.
Here 13 is a lucky number, 17 is the disgraced one... Maybe into your culture it's the opposite.

I know about the differences of the big twin meaning into Harley world, but in italian you call a twin (an engine with two cylinders) "bicilindrico", and big (intended for displacement) is "grande" or its synonim "grosso". So "grande/grosso bicilindrico" litterally is big twin.

Closeing the literal parenthesis...

...Coming back to the exhausts; yes the crossover concerns pulse waves and resonance, but the purpose is to control them and vehicolate or profit of them to extract more power from the engine. Expecially the emptying of the combustion chamber during the exhaust phase is very important. Positive (from the exhaust port to the pipes outlet) pulses crates waves that can be used to have an hoover effect that make easier and faster this job, leaving the combustion chamber more clean. If a negative pulse occur during the last instants of the exhaust phase, you have a negative pressure that can oppose against the piston pressure that is pushing the exhaust gases out from the chamber. Having a well empty chamber is important to accomodate more room for the fresh intake gases of the next intake phase.
So during pipes engineering it's important to study the pipes dimensions and eventually its crossover position to avoid a negative pressure occurs during the final exhaust phase, and maybe trying to create a positive pulse to help extracting exhaust gases from the combustion chamber.

--
Mr. Mechano
Kawasaki ZRX1200 152hp
Tomorrow (yeahhhh) '04 XL1200C red/silver

[stevo]

For peak HP numbers a cross - over pipe does not much at all....

Have a look at a lot of race systems for jap bikes...

The cross-over pipe on a Harley helps with dampeneing the nasty, strong pulses around 2500...

Typically

good mufflers and the stock cross-over are good around 2500 and continue to make power in a fairly linear fashion

2-1 tends ot have a dip in the curve round 2500-2700 and has a rise around 3500 and then continues to make good power

Drag pipes tend to be near useless under 4500, then is the lengths and diameters are correct lots more power can be than most other systems..


As you will know from your previous tuning experiance on jap bikes, many thing have an effect on where and how effective a pipe is.....

HD's due to the 45* and common plenum have particular idiosyncrasis and the cross over helps dampen these around the low to mid, where most people ride...

[Mechano]

For peak HP numbers a cross - over pipe does not much at all....
Have a look at a lot of race systems for jap bikes...
The cross-over pipe on a Harley helps with dampeneing the nasty, strong pulses around 2500...
Typically
good mufflers and the stock cross-over are good around 2500 and continue to make power in a fairly linear fashion
2-1 tends ot have a dip in the curve round 2500-2700 and has a rise around 3500 and then continues to make good power
Drag pipes tend to be near useless under 4500, then is the lengths and diameters are correct lots more power can be than most other systems..
As you will know from your previous tuning experiance on jap bikes, many thing have an effect on where and how effective a pipe is.....
HD's due to the 45* and common plenum have particular idiosyncrasis and the cross over helps dampen these around the low to mid, where most people ride...


Yes, the most professional become the bike usage, the most small become the cross overs. There's not cross over for professional racing exhausts, but sometimes you find a 4-2-1 schema where the position of the 4-2 join is very important.
And every engine is a lot different so some of them need 4-1 schema, some others run better with a 4-2-1. And for some engines you choose 4-2-1 or 4-1 for the particular application you need.
And also different type of racings need different tunings.

Thank you for the explanation.

--
Mr. Mechano
Kawasaki ZRX1200 152hp
Tomorrow (yeahhhh) '04 XL1200C red/silver