How important is the exhaust crossover pipe?

[Guest]

Basically, I am not going to invest the money right now in a new exhaust. That being said, is it extremely important that the crossover pipe stays intact? On mine, its completely falling apart due to rust (not sure why) but the rest of the exhaust is very much intact.

Basically, do I really need to go through the hassle of replacing the pipe, or can I simply cut it out and patch the holes. If I put a new piece in, I have to make sure I get every measurement exact so that everything fits back again, I'd really like to avoid that if possible.

[tkent02]

It's not important at all. Cut it out.
Next time you synch the carbs make them all the same.

[twotimeGSr]

My 79 never had one. Why was it added on 80s?

[tkent02]

Emissions thing I think.

[Steve]

My 79 never had one. Why was it added on 80s?

Generally speaking, a crossover would spread out the torque band, but that would be when it joined both sides of the engine, not just two cylinders.

I have never heard from any authority on the subject, but after having removed a few crossovers myself, the only change that I have noticed is a change in the exhaust note.

What bike do you have? Removing the crossover is SUPER EASY on an 850.

.

[growler]

I wouldn't mind removing my crossover either. It's not rusty at all, but if it doesn't have an impact on how it would run (I'd of course sync carbs after removing it) I'd like to take it off as well. I have an 850, so super easy sounds even better.

Generally speaking, a crossover would spread out the torque band, but that would be when it joined both sides of the engine, not just two cylinders.

I have never heard from any authority on the subject, but after having removed a few crossovers myself, the only change that I have noticed is a change in the exhaust note.

What bike do you have? Removing the crossover is SUPER EASY on an 850.

.

[growler]

exhaust note went lower or higher?

the only change that I have noticed is a change in the exhaust note.

[wymple]

Got rid of mine, only difference I see is oil plug access is easier.

[Dave8338]

exhaust note went lower or higher?

Should be higher in pitch as there is less volume.

Not positive as I've left mine intact.

[Steve]

exhaust note went lower or higher?

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.

I wouldn't mind removing my crossover either. It's not rusty at all, but if it doesn't have an impact on how it would run (I'd of course sync carbs after removing it) I'd like to take it off as well. I have an 850, so super easy sounds even better.

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.

.

[growler]

Thanks, Steve. Especially for the photos. I'm adding this to my whiteboard. (Which is also full of everything else I keep adding)

[850GT_Rider]

Generally speaking, a crossover would spread out the torque band, but that would be when it joined both sides of the engine, not just two cylinders.

I have never heard from any authority on the subject, but after having removed a few crossovers myself, the only change that I have noticed is a change in the exhaust note.

What bike do you have? Removing the crossover is SUPER EASY on an 850.

.

Just makes one wonder why Suzuki added the crossover to a working design, from '79 to '80.

Certainly not cheaper to make with the crossover, so it had to be the result of some engineering directive, and the engineers would have had to show a positive cost/benefit OR some mandated need, for mgmt to approve the extra dollars. Since the crossover doesn't appear to appreciably improve performance, and the change in sound is neglible, perhaps some slight emissions improvement at the time?

[DPage]

This thread seems to lean toward taking out the crossover, but FYI they still sell them on OEM parts fiches. For an '82 850G, it's called a "pre muffler", part # 14210-45201, and costs about $130. So if you want to stay original they're still available.

[srg]

I work with a guy who explained this once to me. All I got out of it was "they constantly suck each others." At that point, I cracked up laughing and walked away. English wasn't his first language, but he was a really smart guy.

Trying to recall what he said, I believe it has something to do with the back-pressure waves of the exhaust. When the "slug" (to use that term) of exhaust pressure flows out of one cylinder and down the pipe, as it passes the crossover, it creates a slight vacuum for the attached cylinders. If there's any plumbers here, that's the entire purposes of the exhaust vents in a drainage system - to relieve that vacuum as the "slug" of fluid goes by. When those attached cylinders are in their exhaust stroke, the slight vacuum makes it a bit easier to "push" the exhaust gases out.

Kind of the opposite of how turbochargers work: the exhaust pushes a turbine (which pressurizes the intake gases), but that act of pushing the turbine takes away from the engine performance because the exhaust stroke steals more momentum from the crankshaft (that energy is being used to push the turbine). The tiny vacuum the crossover creates makes it easier to push the exhaust gases out, thus using less energy.

The person who explained it to me was a car mechanic; obviously motorcycle pipes are much shorter and have smaller engines with higher RPMs (not enough time in between strokes for the air pressure to "flow"), so the effect would be much less.

Now, the firing order and number of cylinders obviously has a significant impact on how effective this would be. But I have too much on my mind to think about that now :-P

[Steve]

You know, srg, that would make a lot more sense if they moved the crossover back a few inches, past the connectors where #1 meets #2 and #3 meets #4. That goes along with the engineering in the automotive world, at least until the "X" pipe came along. The fact that they put the crossover just between #2 and #3 is the puzzling part.

I seem to remember that my '77 KZ650 had a crossover pipe, but it was after the two joints, as I mentioned just above.

.