Question about crossover header tube

[Tapatio]

What does the crossover tube do? I've never seen one on other twins and the only thing it seems to accomplish is to gather dirt. Remus and Sebring headers eliminate it so it doesn't seem a necessary component.

 

 

 

[Firefight911]

Crosstubes have the purpose of enhancing exhaust flow in the mid range. By way of exhaust "pulses" they create a scavenging effect and help move gasses along the pipe. This can aid in the drawing of exhaust gasses out of the combustion chamber and, in turn, create a negative pressure to aid in the drawing in of a new air/fuel charge. You don't see them on "performance" exhausts as their focus is in the upper end of the power band where exhaust gasses are moving along at a higher velocity.

 

I am sure one of the engineer (not caboose) types will chime in to help clarify my very lay response.

 

 

[mneblett]

Crosstubes have the purpose of enhancing exhaust flow in the mid range. By way of exhaust "pulses" they create a scavenging effect and help move gasses along the pipe. This can aid in the drawing of exhaust gasses out of the combustion chamber and, in turn, create a negative pressure to aid in the drawing in of a new air/fuel charge. You don't see them on "performance" exhausts as their focus is in the upper end of the power band where exhaust gasses are moving along at a higher velocity.

 

I am sure one of the engineer (not caboose) types will chime in to help clarify my very lay response.

 

Actooly, a very good summary. As to their value in enhancing real-world driving performance, BMW has used a front cross pipe since at least the earliest /5's (circa 1969), and later added a second cross pipe behind the engine on some bikes (later supplanted by the big collector boxes on the single-muffler abikes). You could always try removing the cross pipe and blocking off the headers to see how mid-range is affected, but I can tell you now it would be a waste of time

[ShovelStrokeEd]

They have a very important function in that they help smooth out peaks in the torque curve caused by very strong pressure waves that move up and down the primary pipes (at the speed of sound, BTW). Quite a few aftermarket high performance exhausts do something similar. At least on the multi-cylinder bikes.

 

One of the bugaboo's of tuned exhausts and radical cam timing can be something called reversion where the returning pressure wave up the primary pipe actually pushes the intake charge back up the intake tract. Undesirable for many reasons. A properly designed crossover can take this pulse and use it on another cylinder to aid in scavenging that cylinder while reducing reversion in the original.

 

HD's have all sorts of problems with this when the boys go to big pipes and hot cams due to the design of the intake tract and the firing order of that 45 degree V-twin. Back in the day, when we all ran either bored out Linkerts or the S&S copy of the same with a big ol' velocity stack on the mouth of the carb, it was not unusual to see a 3" ball of fuel fog sitting at the entrance to the stack. You would know to look down for it as the engine would be running like crap.

[Rich06FJR1300]

that is just such bad spelling of that word i can't ignore it....actooly?

 

ACTUALLY

[Warren_H]

Since that was post 666 the devil made you do it right.

[mneblett]

that is just such bad spelling of that word i can't ignore it....actooly?

 

ACTUALLY

{overhead speaker voice} Need a sense of humor check on aisle 3! {overhead speaker voice OFF}

 

It's intentional -- I see so many posts with folks misusing the language (not knowing the difference between "brakes" and "breaks," for example), that I feel the need to rebel now and then

[AZgman]

Apparently you don't know Mark, (MHN). He is no fool...

[JayW]

I see so many posts with folks misusing the language (not knowing the difference between "brakes" and "breaks," for example), that I feel the need to rebel now and then

 

Me to!

 

Jay

[FLTRI]

Holy thread drift, Batman! Four posts into an engineering thread it turns into a discussion on spelling.

 

You guys make me laff...

[RamblinBoy]

Come, now, where's your censor of humor?

[Dale_K]

Lots of other bikes have them. Most, maybe all, stock Harleys, Triumphs twins have them. It lets exhaust pulses from either cylinder go out both mufflers.

[Mister Tee]

That clears up some confusion on my part. I always assumed that cross piece was just a structural brace, I didn't know that it actually flowed through.