Exhaust Question, for the Engineers & Wannebee's

[Tom MLC]

Can anyone explain the purpose of the crossover section in the stock exhaust system, specifically on the '80 GS1100E. I'm sure other models have it, too. My '78 GS1000's all have it, but much smaller.

If I had to take a stab at answering my own question, I would say it's to minimize competing pressure from two adjacent cylinders. Say 1&2, and 3&4. Sort of like giving the pressure someplace to go so they don't fight inside the muffler.

Now the reason I ask is this. I want to install these mufflers on a set of stock header pipes.http://cgi.ebay.com/ebaymotors/ws/eB...3492750&rd=1,1 My goal was to have them welded on to make a 4 into 2 system, with 1&2 and 3&4 pipes individual units. That would almost certainly eliminate the crossover section because of its location.

If I absolutely must have the cross over section then the whole thing gets a bit longer. And I must add about a 6 inch section of pipe to the 1&4 exhaust. That would affect the exhaust tuning, yes? And would also mean I can't weld the pipes. Gotta use clamps instead. Cant see trying to R&R the entire system as one whole unit. Can you?

Any advice would be appreciated. But, Uh...keep it simple. Okay?

[BentRod]

Hey. I'm a mechanical engineering student so I may be able to help ya (Although there are many, very well informed persons on this website who know what they are doing) I own a 81 gsx400L so I'm not really sure what you mean by cross over section. are you refering to the lateral pipe connecting the left and right sides? or some other bit?

[mixongw]

The way I understand it, it is strictly for the scavaging effect. When one pipe is pulsing it's cylinder, the other is at a neutral or vacuum. I have also heard that it only helps with low RPM operation.

[Tom MLC]

Hey. I'm a mechanical engineering student so I may be able to help ya (Although there are many, very well informed persons on this website who know what they are doing) I own a 81 gsx400L so I'm not really sure what you mean by cross over section. are you refering to the lateral pipe connecting the left and right sides? or some other bit?

Yeah, that's what I'm talking about. In the picture here, which is from a GSR Brother's post (thanks Tornado), you can see the crossover section between 2 & 3.


Not the red circle. That's Tornado's artwork!

So to re-iterate the question. Can I eliminate the crossover, and weld my new mufflers, making 1 & 2 a complete piece, and 3 & 4 a complete piece?

[BentRod]

its about 3:30 in the morning, but i may not be able to get back to you for a while, so I'll give ya some of my thoughts, and may be you can make a call on if it is important.

There is a good chance that it is for balancing pressure in the exhaust. I have one on my gsx400, and I have a sneeking suspicion that it creates a vacume (Max' may be onto something) in the neighbouring pipe.

how important is it? well, depending on your set up you may be able to spilt that cross pipe open half way through. block it off, and then run you motorcycle. don't go riding from NewYork to Chicago on it, but see if you notice any difference in noise, feel, acceleration.


On another note though, you said it would add 6 inches to your exhaust length?, why not just move the cross piece up a bit? say 3 or 4 inches. this will leave pleanty of vacume space in the down pipe for exhaust gas to move into and benifit from the vacume. it wont be as strong a vacume, but it sure as heck will be a lot better that taking it off completely.

NOW TO THE REST OF YOU! there has to be a Mech Eng in here some where. I know Thermal Fuilds can be a B1tch, but someone must remember it!

[salty_monk]

In my manual it describes it as a "pre muffler"... could it not be just that? Some addition by Suzuki as the cheapest way to meet some sound regulation without adding a lot of cost or changes to the bike?

Can't see it making a lot of difference anywhere else apart from adding a restriction. My 80 1000g has it but the pipes I have for a 750 are all separate...

Dan

[BentRod]

if you are going to compare with the 750, then you have to be prepared to live with the assumption that the two engins are Identicle in scale, and any consiquences that may bring.

Why don't you take it apart and see whats in side? I'll bet it's just a pipe. and if it were a "Premuffler" to try and slide in under noise laws, why don't 1 and 4 have it? also, there really isnt anything cheap about adding an additional part like this one, infact its a pain in the a$s, and is costly. better to modify an existing system, then throw in a wrentch like this if noise is the problem.

sounds like you REALLY don't want it there.

I'm very hesitant to give you anything concrete because it is very hard to know. if it does have anything to do with creating vacume pressure, then it is a bit of a delicate balancing act.

I still recommend you disconnect and the block that cross piece, and test it out. you are the one who has to live with any consiquences, so if you have the opportunity to test it out befor hand then i don't see why not

[Dink]

It is simply a "torque box" it helps to balance and smooth out exhaust pulses across the four cylinders, removing it will create a bit of a flat spot in the powerband, similar to the loss experienced when you fit a 4 into 1.

Dink

[Tom MLC]

In my manual it describes it as a "pre muffler"... could it not be just that? Some addition by Suzuki as the cheapest way to meet some sound regulation without adding a lot of cost or changes to the bike?

Can't see it making a lot of difference anywhere else apart from adding a restriction. My 80 1000g has it but the pipes I have for a 750 are all separate...

Dan

Dan, that's the reason I was interested in those pipes. Four individual pipes would have made the project easier.

I really don't want to cut up my stock system. I recently picked up another stock set of pipes without the mufflers. I plan on experimenting with them.

Thanks everyone, for the advice. I won't be starting right away, so if there are any more opinions or advice, keep 'em coming!

[koolaid_kid]

I agree with Dink, since other (bike and car) manufacturers call it a balance pipe.
For stock exhaust, I would keep it in. For aftermarket exhaust, it is not required nor used.
Best of luck, and keep us informed.

[Carter Turk]

Some of the older Yosh 4-1 pipes had cross over chambers for all 4 cylinders, supposedly there to eliminate or lessen the flat spot and improve low to midrange grunt. They were located somwhere near the base gasket level of the engine.

Katman had one these for sale a few years back.