running engine without exhaust pipe?

how can running your engine wihout a pipe hurt it don ohio just informed me that it could but I don't understand how... anyone?

Re: running engine without exhaust pipe?

Jason Luther /

its all about air flow. without a pipe, there is no backpressure in the exhaust, so the air is able to escape better/faster. therefor air is better able to enter the motor. since your two-stroke engine relies on the fuel for its lubrication, more air means your air/fuel mixture is too lean(not enough fuel) therefor your engine isnt getting the lubrication it needs. you can get a bigger jet, thus letting more fuel, or you can put your exhaust back on since its probably too loud and obnoxious anyway.-jason

Re: running engine without exhaust pipe?

I intended too I was just running it withou exhaust for testing purposes cause I thought my exhaust was clogged since my moped wouldn't run over 5mph with it on so I took it off and it did about 40 so I think the pipe is clogged...just a guess I really doubt all that extra air made it go that fast but I dunno

Re: running engine without exhaust pipe?

If more air is coming in, it's gonna pick up more fuel/oil too.. Ultimately I come to the same (lean) conclusion as you, Jason, but for a different reason.

It's well known that heat damage comes from too much backpressure. This pressure build up alters compression and directly heats the piston and can cause a meltdown, especially with an expansion chamber and high power outputs.

Opinions about whether or not (and exactly how) too little back pressure can do some damage varies widely..

i have run without any exhaust on a PA50 for a couple miles and didnt have any problems and didnt feel anything odd... (but i didnt do a plug chop either.) It was just an experiment to see what would happen with top speed limit.

Without the muffler the bike's top speed went from 30 to 37mph (!). So here's what i think..

If some engine suffers by having zero exhaust restriction it's because of high RPMs.. and a carburetor that forces a lean mix at those higher rpms.. That engine is spinning a lot faster than it should and a lean fuel means not enough lubrication.

A bigger carb or main jet would cure it. This says that low backpressure is not the problem. A lean mixture is the actual problem.

I can't imagine how ONLY less exhaust restriction by itself creates more heat..

But i can imagine how the effects of running with low back pressure on some particular bike and engine might cause other things to happen, and that causes something else to happen.. ultimately resulting in possible heat damage.

Re: running engine without exhaust pipe?

Just runnin for a few minutes wont hurt. but don''t try to drive the ped. you can fire the ped up for a minute and then turn it off before it gets too hot.

Re: running engine without exhaust pipe?

i really doubt that running without an exhaust (without exceeding normal top speed) is gonna do anything.. All my bike did was accelerate normally (slowly) while being loud as all hell. .. the funny thing was top speed kept climbing, slowly but surely.

And a bike that steadily increases speed way beyond normal is not the sort of thing that happens when a cylinder/piston is overheating.

but, to be fair, i'm just as clueless as everyone else until someone actually does the experiment and documents the results. Any volunteers?

Re: running engine without exhaust pipe?

I dunno I rode around maybe 30 minutes today on it climbing hills and stuff didn't seem to do anything. sounded fine other than being loud the whole time. I don't know if I ever made it to top speed though I was just putzen around it didn't seem to have anything wrong afterwards not abnormally hot or anything to my knowledge I could hold my finger on the cylinder about 5 seconds before it started to burn(thats my redneck thermometer LOL) but I remember on the bike before I rebuilt everything, running and just driving it around it got alot hotter than that...but yeah maybe it not a good idea I thing maybe chris from mwh's input is needed here

Re: running engine without exhaust pipe?

Whats needed is someone actually tests the theory in a scientific manner and puts the question to rest once and for all... or find some documentation from an authoritative source that says low backpressure causes problems.

Re: running engine without exhaust pipe?

No, I'm tellin' you,Tom, that when you have a cyl. and piston at 900-1200 degrees, and you shut it off, the inrush of cold air (NOT being preheated from a pipe) back into the cyl. can warp the piston,rings, or cylinder. If metal cools too quickly,damage can result.

I would never chance can do what you want. don-ohio (:^)

Re: running engine without exhaust pipe?

2-strokes need an exhaust that's tuned to the proper resonance for optimum performance asnd power in certain rpm bands. Running a 2-stroke without a pipe is usually not nearly as good as having a `tuned' pipe. I believe `MacDizzy' explains this well on his tuning site. don-ohio (:^)

Re: running engine without exhaust pipe?

yeah I know that without the back pressure you get crappy performance and what you said about the cooling makes since I understand what your saying now...yeah I just did it once to test but for sure it's getting a pipe before I ride it again thanks don

Re: running engine without exhaust pipe?

Sure! I hope you get `er runnin' like a `scalded dog'! LOL! don-ohio (:^D

Re: running engine without exhaust pipe?

mwh says techno estoril pipes in the mail and thats all I need

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