exhaust h-pipe - why?

[xjwmx]

Don't know about earlier models, but the Specials have a crossover pipe in the exhaust. Is it really beneficial? Since both cylinders are exhausting at the same time it seems like it might cancel the presumed advantage of more muffler and freer exhaust per exhaust cycle.

EDIT -- they aren't exhausting at the same time.. Brain fart.

 

[650Skull]

76 Was the first year of the crossover.

 

[5twins]

They don't exhaust at the same time. One is firing when the other is exhausting. Crossovers in the exhaust are supposed to benefit midrange power but the closer they are to the head, the more beneficial they're supposed to be. My best guess about the Special crossover is added noise suppression, the combining of 2 smaller mufflers. But the Standard mufflers use one too so I'm really not sure why it's there. Maybe we're back to the better power output thing.

 

[xjwmx]

You're right -- they aren't exhausting at the same time. Pardon the brain fart. Had my mind on other things this winter. The pistons move together but the valves move one rotation of the crank differently.

 

[grizld1]

Don't know why Mama Yama used the crossover, but you won't see an XS650 race bike or many aftermarket performance exhaust systems with it. Bub omitted the crossover. Since they spared no expense and charged a premium price, they didn't leave it off to make their system cheaper. The only crossovers I've seen on XS650 aftermarket exhausts have been the Campbell X-pipe (much snake oil in the marketing) and the old Kerker 2-1. The Kerker crossover was a very small tube just before the first bend of the headpipes--around 1/2" ID if memory serves. Don't know that it did much.

 

[XSLeo]

From what I have read, the crossover is supposed to improve scavenging at low to mid rpm's.
As each cylinder's exhaust pulse goes down the pipes there is a positive pressure in front of the pulse and a negative pressure following the pulse. As these pluses pass the crossover the positive pressure ahead of the pulse passes through the crossover it can't go back up the other pipe, valve closed, so it helps push the exhaust out of the pipe.
The negative pressure behind the pulse crosses over and helps pull exhaust out of the head when the exhaust valve opens.
These negative and positive pressures alternate side to side as the engine runs. They only help at lower rpm's because at higher rpm's the exhaust if flowing fast enough so the effect is very minimal.
An exhaust engineer may have charts and tables that can show how much effect this scavenging has, but for us on the street can we tell the difference, I can't.
My buttdynometer isn't that well calibrated.
Leo

 

[rick1956]

From what I have read, the crossover is supposed to improve scavenging at low to mid rpm's.
As each cylinder's exhaust pulse goes down the pipes there is a positive pressure in front of the pulse and a negative pressure following the pulse. As these pluses pass the crossover the positive pressure ahead of the pulse passes through the crossover it can't go back up the other pipe, valve closed, so it helps push the exhaust out of the pipe.
The negative pressure behind the pulse crosses over and helps pull exhaust out of the head when the exhaust valve opens.
These negative and positive pressures alternate side to side as the engine runs. They only help at lower rpm's because at higher rpm's the exhaust if flowing fast enough so the effect is very minimal.
An exhaust engineer may have charts and tables that can show how much effect this scavenging has, but for us on the street can we tell the difference, I can't.
My buttdynometer isn't that well calibrated.
Leo

H-pipes were pretty popular on early Mustangs for that same reason.

 

[jetmechmarty]

From what I have read, the crossover is supposed to improve scavenging at low to mid rpm's.
As each cylinder's exhaust pulse goes down the pipes there is a positive pressure in front of the pulse and a negative pressure following the pulse. As these pluses pass the crossover the positive pressure ahead of the pulse passes through the crossover it can't go back up the other pipe, valve closed, so it helps push the exhaust out of the pipe.
The negative pressure behind the pulse crosses over and helps pull exhaust out of the head when the exhaust valve opens.
These negative and positive pressures alternate side to side as the engine runs. They only help at lower rpm's because at higher rpm's the exhaust if flowing fast enough so the effect is very minimal.
An exhaust engineer may have charts and tables that can show how much effect this scavenging has, but for us on the street can we tell the difference, I can't.
My buttdynometer isn't that well calibrated.
Leo

What I have read tells me that where the crossover is placed depends upon what RPM scavenging needs to be increased.
How about this?