Do I need an exhaust?

I am repairing my 197? Motobecane Cady. I'm wondering, If i do get the engine runnijng, do I need and exhaust pipe for it? Cause right now I don't

Re: Do I need an exhaust?

Mike Scouty McScoutington /

do you want dirt and other such stuff working its way into your engine? i didnt think so. yes you do need a pipe. whats more it is deffeningly loud without a pipe.

Re: Do I need an exhaust?

Yeah, its handy

Re: Do I need an exhaust?

Unfortunately, two strokes are always gonna be a lot louder than a comparable 4-stroke bike. Two-strokes are also under fire due to more exhaust pollution. For these reasons, new two stroke bikes (and boats) have already been banned in a lot of places..

If we all go riding around without a pipe (!!??) or silencer/muffler and upset the neighbors (most of whom vote), they might just pass another law that lets them confiscate all two strokes they catch on the street...

My guess is it'll happen worldwide anyway within 10 years or so.. but thats only if everyone is really careful about noise..

Anyway, a simple tapered/cone shaped pipe, with no baffles inside, will really help power. The cone (diffuser) will pull exhaust gases out of the cylinder. This will provide a cleaner fuel mixture to be trapped in the cylinder, and a lot more power will be produced. When followed by a good muffler, the bike will also be fairly quiet.

Re: Do I need an exhaust?

Leon Swarmer /

also running an engine without an exhaust system can really mess it up because of heat/cooling cylces

Leon

Re: Do I need an exhaust?

well.. we're currently debating this issue in another THREAD break>

If you can explain exactly why an open exhaust would cause some kind of damage or upset proper heat cycles or whatever, i'd like to hear it.

Re: Do I need an exhaust?

Those Cady exhausts are hard to find huh? I just got a Cady in on Friday, and UPS crushed the exhaust. Luckily I had an M1 laying around, so I stuck that exhaust on it. I've been searching for a replacement ever since with no luck. Let me know if you find one!

Re: Do I need an exhaust?

The idea goes back to the old theory about 4 stroke engines running on headers only. The thought was that the exhaust was so short that when the engine was shut down cold air could be sucked back into the header and crack the exhaust valve. I never heard of it happening though.

Re: Do I need an exhaust?

I think I found one on www.themopedjunkyard.com

Re: Do I need an exhaust?

i remember something like that.. It was about valve overlap.. especially with a high lift / duration performance cam.

Without enough back pressure, some frresh mixture was lost out the exhaust valves.

Re: Do I need an exhaust?

He doesn't sell the bolt on ones, just the screw-on like the 50 models.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

On 4-strokes, you can run long headers but even a leaking exhaust manifold gasket will make the engine run lean(hot) due to valve overlap. Jim.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

Check the attachment for short headers. Jim

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

Forget the short headers, it didn't work, sorry. Jim.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

Re: Do I need an exhaust?

if u run with no pipe thats almost the worst thing u can do other than putting sugar in your gas tank i ran without a pipe for a wile with my cady wow its loud

Re: Do I need an exhaust?

it's interesting that you compare the danger of running without an exhaust to putting sugar in a gas tank..

fact is that sugar in a gas tank does no harm . Sugar doesn't dissolve in gasoline so it just sits in the tank.

Check it out at Snopes break>

Now we gotta wonder if the thing about the exhaust is just another urban legend.

If someone can explain, in scientific terms or with logic why a 2-stroke needs backpressure, speak up.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

http://www.eric-gorr.com/techarticles/basic_two_stroke.html this is the simplest explanation I have found to explain why back pressure is needed in order to get maxium power out of a 2-stroke. I also think there is some exhaust gas recirulation(EGR) as used in automobiles to reduce heat in the cylinder. I have posted this before so you may have already read it. Jim.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

Hey Joew, The problem arises because the exhaust valve is about to close(low pressure) and the intake valve is starting to open(low vacuum). If the exhaust port is open to the oxygen rich atmosphere some air will be drawn into the cylinder instead of 100% fuel/air mix from the intake manifold causing a lean condition. Jim.

Re: Do I need an exhaust?

the question is not if a 2-stroke needs a proper exhaust system to develop maximum power..

the question is whether or not running with a wide open exhaust port can damage an engine, and if so, how and why.

Or, just explain why a 2-stroke RC engine, turning 20,000+ rpm on nitromethane does not need or use any exhaust system but a moped engine would..

Re: Do I need an exhaust?

if you want a thorough explaination and the theory behind tuned exhaust systems on four stroke engines, i recommend A.G. Bells companion book to two-strokes.. "Four-Stroke Performance Tuning" .. he devotes quite a bit to this topic.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

Joey, you said,just explain why a 2-stroke RC engine, turning 20,000+ rpm on nitromethane does not need or use any exhaust system but a moped engine would..--- I performed a quick search on RC engines and found nothing on exhaust systems except to reduce noise so it appears to me the main reason for an exhaust system on a ped is to increase power. Running an open exhaust reduces power but probably won't harm the engine Jim.

Re: Do I need an exhaust?

On an RC, there is ane exhaust pipe, with a backpressure line going from the pipe to the fuel tank. This is what pushes the fuel. Without a pipe, the engine will get no fuel, causing it to run very lean, and overheat.

Re: Do I need an exhaust?

Steamboat Aka J. R. Stevens /

Rick, Do you mean the back pressure is being used as a fuel pump? If so this would not apply to a moped which uses gravity feed. Jim.

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