How important is the exhaust crossover pipe?

[tkent02]

They started the crossover the same year as they went to CV carbs on most models. I bet it was an attempt to create the illusion that it still had the same throttle response that the earlier bikes with VM carbs had. A little more low end grunt so it feels like the power is coming on quicker, so the aggressive rider won't notice the throttle lag as much. Also a slight bit more efficiency at low RPMs to help with emmisions testing, as emissions was the main driver for the new CV carbs anyway. Maybe the crossover allowed it to run acceptably with slightly leaner carburetor settings.

I guess we will need to talk to the retired Japanese engineers who finalised the designs for these bikes thirty five years ago to know for sure.

[Killer2600]

They started the crossover the same year as they went to CV carbs on most models......Maybe the crossover allowed it to run acceptably with slightly leaner carburetor settings.

I guess we will need to talk to the retired Japanese engineers who finalised the designs for these bikes thirty five years ago to know for sure.

Ok, that's a theory, now tie that all into what we have as fact and all your previous thoughts - Jet sizes being equal among all carbs except for the 1150, an uneven factory carb sync spec, a crossover that joins the inner pipes upstream of the 2-1 that joins the left or right pair. In other words, sell your theory because we aren't going to find the person who came up with the design and even if one of us did find the creator everyone else is still going to be a doubting thomas.

[Steve]

... I guess what they made was good enough to trust your life on, everything in your stable originates from their corner of the globe. . ...

Almost everything.

Although it may wear a name badge that originated "over there", my Wing was built less than 100 miles from me.

Not just assembled, either. The engine blocks were cast in a building just down the road, the transmission gears and cranks were machined next door, the plastic pieces were injection molded on-site. A few things, like tires, suspension bits and gauges, came from other sources, but most of it was actually made "right here" in oHIo.

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[tkent02]

Ok, that's a theory, now tie that all into what we have as fact and all your previous thoughts - Jet sizes being equal among all carbs except for the 1150, an uneven factory carb sync spec, a crossover that joins the inner pipes upstream of the 2-1 that joins the left or right pair. In other words, sell your theory because we aren't going to find the person who came up with the design and even if one of us did find the creator everyone else is still going to be a doubting thomas.

Nah, I don't care either way. I only have one bike with a crossover, and it runs just fine with all four carbs set the same. OK power, OK gas mileage. The rest of the bikes without them are the same.

The part about the center cylinders on the eight valve GS getting hot enough to require richer jetting is pure BS.

[JAG]

Applying that whole concept would mean the exhaust traveling backwards (up the pipe) and a longer distance till exit would be more efficient i.e. the path to get from the #1 cylinder to the right side outlet.

Nope you've lost me there.

Imagine a steady state system frozen in time. Measure the pressure in each header at equal distance from the exhaust ports. Disregarding any slug of hot gas, the ideal situation is for the pressure in each tube to be equal. If similar equal flow/pressure characteristics are achieved across the induction, compression and combustion phases, then the engine will be fundamentally balanced. Fine tuning of individual carbs will allow for slight variations in each individual cyclinder.

A multicylinder engine is, in effect, several engines, connected at the crank, running simultaneously. To ensure maximum efficiency of the combined engine arrangement, each individual heat engine (cyclinder assembly) must be closely balanced to the others. If not power is lost as one tries to push the other.

Balancing of the carbs can be achieved in the factory to get a base flow characteristic. Individual carbs are then balanced to each other. Balance across the cylinders can be achieved by machining to set tolerances. Balancing of the exhaust depends upon the pipe design. A 4:1 naturally achieves this if header pipes ate of equal lengths and all join the collector at the same place. For a 4:2 system its more complicated. Some form of balancing pipe / box is required. Where that sits is immaterial as we're talking about baseline pressure not the route of the exhaust gasses.

As I said. Its complete bull**** but I buy into it. In short the balancing pipe is not critical. It may at worse slightly reduces the efficiency of a 4:2 system.

[850 Combat]

All of mine have crossovers, except maybe the 1000E. I certainly don't care either way. I replaced a worn out exhaust system on my favorite 600 dollar 850G with a pretty nice one off this list. I couldn't get all three of the bolts on the pre-muffler/crossover to line up at the same time, so its only got two installed. I can't believe that it needs any at all.

[GregT]

Nope you've lost me there.

Imagine a steady state system frozen in time. Measure the pressure in each header at equal distance from the exhaust ports. Disregarding any slug of hot gas, the ideal situation is for the pressure in each tube to be equal. If similar equal flow/pressure characteristics are achieved across the induction, compression and combustion phases, then the engine will be fundamentally balanced. Fine tuning of individual carbs will allow for slight variations in each individual cyclinder.

A multicylinder engine is, in effect, several engines, connected at the crank, running simultaneously. To ensure maximum efficiency of the combined engine arrangement, each individual heat engine (cyclinder assembly) must be closely balanced to the others. If not power is lost as one tries to push the other.

Balancing of the carbs can be achieved in the factory to get a base flow characteristic. Individual carbs are then balanced to each other. Balance across the cylinders can be achieved by machining to set tolerances. Balancing of the exhaust depends upon the pipe design. A 4:1 naturally achieves this if header pipes ate of equal lengths and all join the collector at the same place. For a 4:2 system its more complicated. Some form of balancing pipe / box is required. Where that sits is immaterial as we're talking about baseline pressure not the route of the exhaust gasses.

As I said. Its complete bull**** but I buy into it. In short the balancing pipe is not critical. It may at worse slightly reduces the efficiency of a 4:2 system.

Sorry but I'm falling off my chair laughing....I've been building and dynoing race pipes for around 30 years and never heard or tried "balancing the exhaust".
FWIW the crossover pipe is fitted to enable more restrictive(quieter) mufflers to be used as the total system flow is then divided between two outlets.
Successful troll though.....
this will be my only response to this thread.

[Killer2600]

The part about the center cylinders on the eight valve GS getting hot enough to require richer jetting is pure BS.

It not about overheating or being able to run it's just better efficiency. Air cooled V-twins run just fine and have always done so even with the inherent attribute that the rear jug runs hotter than the front.

As I said. Its complete bull**** but I buy into it. In short the balancing pipe is not critical. It may at worse slightly reduces the efficiency of a 4:2 system.

I can buy into the BS theory on that one, mainly because it throws out many laws of physics.

FWIW the crossover pipe is fitted to enable more restrictive(quieter) mufflers to be used as the total system flow is then divided between two outlets.

this will be my only response to this thread.

My only response to this is the same as above.

This however brings us back to the original question, "How important is the exhaust crossover pipe." Reason leads us to believe if the muffler is too restrictive to only have one then the OP can't just axe the crossover as the bikes ability to breath will have been cut in half.

[tkent02]

I think you are right, it can't be too restrictive, they run just fine without it.

Maybe there is a 1% or 2%b difference a dyno can see, which might have been enough to be worth it to Suzuki back then, but for all intents and purposes, it's nothing.

[JAG]

Sorry but I'm falling off my chair laughing....I've been building and dynoing race pipes for around 30 years and never heard or tried "balancing the exhaust".
FWIW the crossover pipe is fitted to enable more restrictive(quieter) mufflers to be used as the total system flow is then divided between two outlets.
Successful troll though.....
this will be my only response to this thread.

Thanks... I'll just go change my knickers. Pee'd myself in hysterics.

Well I did say at the start it was bull****.

Well after a career of 125 years designing all manner of pipe system... FWIW, and as a side note, how does more restrictive silences benefit the bike? Are you saying by having a connector pipe the exhaust gases from each combustion cycle passes through both cans? How can this be? What evil wizardry drives such things?

I don't get that. Increasing the volume of the pipe will reduce exhaust pressure and hinder evacuation of the cyclinder. Unless of course the pressure drop is insufficient to cause a problem. But then isn't this sharing of the cans actually the same as "a balanced pipe" i.e. the pressure conditions in each individual exhaust route are common across all cyclinders.

Technicians. Gotta love 'em.

[nejeff]

It didn't go any higher or lower, just the cadence changed.

Because of the crossover, if you listen to the end of either pipe (let's pick the left one), you will hear a bang when #3 fires through both pipes, then a BANG when #1 fires through the left side only, a bang when #2 fires through both pipes, then nothing as #4 fires through the right pipe. Of course, the right pipe does the same thing, but oposite in the firing order.
Listening from the middle at the back, you would hear:
...(left) ... (right)
3. bang .... bang
1. BANG
2. bang .... bang
4..............BANG
3. bang .... bang
1. BANG
2. bang .... bang
4............. BANG

After removing the crossover, you would hear:
BANG
BANG
............ BANG
............ BANG
BANG
BANG
............ BANG
............ BANG

It is just a subtle difference, but that is what made it sound like a Suzuki. The new cadence is what they sounded like before 1980, so it's nothing new or radical.



Check with your local auto parts store(s) to see if they have any pieces of 1 1/4" exhaust tubing. Stores around here used to carry them, but now don't carry anything smaller than 1 1/2". The pipe you want will be flared at one end for a slip fit onto another pipe. If you find them, they will likely be 18 or 24", you will have to cut them. If you can not find any in a store, go to a muffler shop, have them cut two pipes for you and expand (flare) one end. You need two pipes that are 7 inches long. I tried 7 1/2" to make sure they overlapped at the joints, but had problems with the excess length.

Here is what they look like. You will also need to cut four slots in the flared end to give it room to clamp down.


Here are the new pipes clamped to the downpipes with the original clamps:


Here is why I had to come up with this repair:


I have done this to two of my bikes and at least two others, so I know that it works well.

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Steve, with this setup are we eliminating the exhaust gasket material then

[OldVet66]

Probably not necessary. You could probably do the same thing on the other end with crossovers on the sync ports between 1-4, 2-3, on the carburetors. It does make a small difference , especially in low end. Triumph and others have done the same with their carburetors.

[Steve]

WOW!!! Yet another thread that has been lying dormant for almost a year and a half has been brought back to life.

Steve, with this setup are we eliminating the exhaust gasket material then

That depends on how tightly your pipes fit. Mine were loose enough that I re-used the gasket from the old pipes and pieces.

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[nejeff]

WOW!!! Yet another thread that has been lying dormant for almost a year and a half has been brought back to life.



That depends on how tightly your pipes fit. Mine were loose enough that I re-used the gasket from the old pipes and pieces.

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My old gaskets are fell apart, should I adjust the pipe size I guess is the question. Probably should take the pipes to the exhaust shop

[Steve]

Just ask for a couple of pipes that are 1 1/4" diameter, 7" long, have them expand one end for about 1 1/2-2". Expand it just enough to slide the other pipe in. When you get home, use a hacksaw to cut some slots about 1" deep on the expanded end, then slide everything together and clamp it up. If your stock clamps are still good, use them. They take a LOT less room than a typical muffler clamp, which will hang down below the bike and get damaged by road debris.

Print out the pictures to show them what you are trying to do.

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