Two stroke exhaust pipes

[jdincau]

Hi all,
      Has anyone out there had any experience building two stroke engine
exhaust pipes? Specifically attaching the exhaust system to the cylinder
barrel. The standard exhaust on the engine we are running uses a ball and
socket joint held together by springs at the barrel. We would like to run a
more gas tight joint but are worried about stress on the barrel. Any
comments?
Jim in Palmdale

[doug odom]

Jim, I would check with the really fast go kart guys. I'm sure they have figured out the best way to power tune and keep them from falling off. I think they still race them at Willow Springs. At one time a go kart held the track record for the fastest lap ever there.    Doug Odom in big ditch

[Jonny Hotnuts]

I have done a fair amount of tinkering with 2smoke pipes. If you are having a seal problem I would recommend cleaning up the cylinder and ball, reinstalling it with more and or heavier springs and make sure the pipe is braced after the fact. The springs are only to keep positive tension on the pipe cylinder joint and are not designed to support the weight of the pipe.

I am confident that if the pipe is supported, has heavier springs on a clean joint you will not have seal issues.

[pookie]

Hi Jim, the pipe is usually supported at the barrel AND the back bumper of a go kart. the reason for the quick release at the barrel is for tuning purposes. We will insert different lenghts of flex tubing to tune the engine to the current racing conditions. What brand 2 stroke engine do you have?  What is the engine installed in and to what purposes is it being used? I have  a few different pipes just sitting around from begone days. Maybe one would be of help to you. No big deal to let you try to see. My shop isn"t to far from you. Let me know. Mike

[jdincau]

Hi all,
     The engine in question is a 125 Rotax spec cart piece. It is going (allong with three others) into a streamliner. I assumed the ball couplings on these things were to serve the same function as on a dirt bike. That being to avoid damaging the engine when the pipe comes into contact with some immovable object. We have used a CAD program to duplicate the factory pipe tapers and lengths in a layout more to our liking. I am getting pretty good at cutting, rolling and welding cones (see below). We would like to use a bolted joint at the barrel to avoid any exhaust leaks in a closed car. The pipe will be supported at several points along its length. I am worried about cracking the pipe due to vibration. We are planning to ask this same question of Mike Manning the Rotax cart guru at Willow springs. He is givings us tunup info.

[stay`tee]

i have had extensive experience with expanshion chambers (design and constructing), in the earlie days on dragbikes and at present on motocross and flattrack,, you have to allow the entire pipe to " float" ,,, the high intensity vibrations from within the chamber cause cracking around any area that is solidly mounted

[Stainless1]

Hi all,
 We would like to use a bolted joint at the barrel to avoid any exhaust leaks in a closed car.

An exhaust leak shouldn't be that big of an issue, the drivers compartment should be sealed from the engine bay.  Are you worried about the charge that flows back from the exhaust creating an explosive atmosphere in the engine bay?  If that is your concern, why not move a little fresh air through there, it can double as cooling... 

[pookie]

Hi Jim, Manning is one of the best, so you are on the right track. If I might add, when mounting the support for the pipe , you can use vibation isolaters, rubber,fiber,or poly bushings. One more thing,   don't forget to allow room for the stinger on the pipe, and possible modifications to the exhaust pipes in the future,on the vehicle. The pipe is one of the most important methods for making horsepower in a 2 stroke, plus a great tuning aid. Swedetech in Elk Grove, Ca. has done alot of work on the dyno with "pipe" design and tuning and have a very good reputation. Jack Costella started using thier engines in the 5050 liner but the liner is so confined in the engine bay he can't do pipe tuning or pipe changes with out a major revamp of the engine bay. A lot of racers just slap on a "header " because they are thinking with a 4cycle mentality where they "just work" and is the last thing that is changed, but in the 2stroke engine the exhaust is the key.  If I may one more thing, when starting the engines, after you have choked the engines, on self start or push, DON"T FORGET to open the throttle to allow fuel to be drawn in to cylinder as it is also the way the engine gets its lubercation. Please excuse this long winded text, I am probabley close to being the 1st person on the site to be banned because of boredom. Yikes, Mike R.

[Hans Blom]

Jim, what are you, and others, using for fabricating your 2stroke pipes? Material that is...

[jdincau]

.035 cold rolled steel. That is the max my slip roll will take.
Jim

[Dean Los Angeles]

The pipe moves at a vastly different frequency than the engine or the frame and will shortly crack any solid mount on the engine or frame. 

There are a number of different slip joints used. Don't worry about leakage. The springs hold pressure against the gasket or o-ring. Don't forget to safety wire through the springs.

[Loose Goose-Terry#1]

The "vibrations" caused by the sonic wave reverberations will cause the pipe to fracture where the pipe thickness changes (i.e. a weld-on bracket). I raced Karts for 25 years and the best luck was either cradling the pipe and attaching it with hose clamps or by finding the balance point and welding a tube through the pipe perpendicular to the pipe centerline and mounting the pipe on a rod between a couple of springs.

  Use various length flex pipe to go from the exhaust header on the cylinder to the head pipe of the expansion chamber. Cut some common screen door springs to whatever length you need to maintain good pressure against your header. The best way to get a seal on your set-up is to use a header pipe with a gasket to your cylinder. Your header should be designed to fit inside the flex about 1.25" and have a shield welded to the header that also fits over the flex by about 1.25". Do the same thing with the expansion chamber head pipe. Unless you are inside a closed compartment it really doesn't have to seal all that well. Exhaust "backpressure" leakage or the lack thereof isn't going to have any affect one way or the other. An expansion chamber works on the principle of tuned sonics to scavenge the cylinder and bring a fresh fuel charge into the combustion chamber.

Terry