Running without Exhaust Cans?

[ResearchRat]

A Ducati Monster owner in my garage runs his bike without cans from his exhaust (Actually there isn't really an exhaust system at all.) His reasoning why: it removed weight, and offered a less restrictive exit path for exhaust gasses to leave the engine.

I'm not intimately familar with the mechanics behind exhaust systems, but do know that exhaust airflow can impact engine characteristics: power/acclearation.

All environmental and potential code violation disscusion aside. Is there any benefit to running without cans?

-RR

[zippythehog]

Most bikes have a crossover pipe of some sort. In a crossover set up, the exhaust charge moves out of the cylinder and creates waves of high and low pressure (crests and troughs-like a rock dropped into a pond). The low pressure waves hit the crossover and create a relative vacuum to help draw the spent charge from the next cylinder out of the combustion chamber after that cylinder's exhaust valve opens. That scavenging is missing if there is no exhaust system.

In older engines, the exhaust valve was the component that was a high wear item. The valve stem would literally burn or oxidize so that the valve head would break off and fall into the engine. In a modern engine, the metallurgy has greatly advanced. However, that new engine is designed by an engineer to be used a certain way, so that it can meet its life limit. If you don't use it the way the engineer designed it, you really can't expect the machine to last or perform as it was designed to.

I wouldn't run it that way. Even racing motorcycles have some type of conduit to route exhaust gasses. Those exhaust gasses are hot. It's leaving a lot to chance to just blow that torch heat around the outside of the engine. Besides, an engine without a pipe usually sounds dumb (bwoop-bwoop). You need some resonance to make it growl and howl.

Zip

[ This message was edited by: zippythehog on 2007-03-27 20:16 ]

[Lone-Rider]

I'll bet that runs like a pig !...A certain amount of back pressure is needed to make an engine run correctly.

[ This message was edited by: Lone-Rider on 2007-03-29 13:35 ]

[TBSstunta]

On 2007-03-27 20:08, zippythehog wrote:
If you don't use it the way the engineer designed it, you really can't expect the machine to last or perform as it was designed to.

Well heck, if that were the case no one should put anything aftermarket on their bike.

I agree that no cans is a dumb idea and he should suggest that the owner of the Monster remove the rear suspension because it adds weight, just weld in a metal rod. Heck those tires don't do anything besides hold the tires on, he could accomplish the same with zip ties, and just think of the weight savings. :-D

[Mojoinco]

Typically you have a length of pipe to keep any cold air from getting sucked up to the valve area. In addition, I would think he is running a pretty lean mixture to do so, even if his injectors theoretically can handle the flow (read through a lengthy discussion of this recently in relationship to Miata's and super or turbo chargers), that's not real world. And it presumes the curves are correctly programmed, etc. But hey, it's his engine and his money. Probably plays hob with his power overall, especially valve overlap.

[zippythehog]

Quote:
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On 2007-03-27 20:08, zippythehog wrote:
If you don't use it the way the engineer designed it, you really can't expect the machine to last or perform as it was designed to.

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Well heck, if that were the case no one should put anything aftermarket on their bike.

Well there is no way that an idividual or even aftermarket manufacturers can hope to put as much R & D into reliability and performance as the OEM. That is part of the reason some modifications estrange the warranty on new machines. Besides we owners and the aftermarket manufacturers don't have the resources available.

The application of bar end mirrors is hardly going to affect engine longevity the way running without exhaust is.

In the end, "you pays your money and you takes your chances."

Zip

[Lone-Rider]

To get an engine to run right [especially a small engine] the exhaust needs to be a tuned length. This length also needs to compliment the cam profile so the engine will respond in a certain power band. Playing with this is fun but, you have to use some sense. On mine, I wanted to keep it's good mid range. I kept the stock head pipe [3 into2] and went with after market cans. The back pressure is lower but, the tuned length is about the same. If you use a 3 into 1 type system, the back pressure is much lower because of much more flow. You still keep the length about the same. You gain more HP on the top end if jetted correctly but you might loose a little torque in the mid range. you pay your money and take your choice.

[ This message was edited by: Lone-Rider on 2007-04-03 13:38 ]

[seumas]

And for most of us a strong mid range does more good than a few extra ponies on the top end.