Tecumseh 2 stroke Mods

Discussion in 'Performance Mods' started by LordKeiella, Jun 21, 2010.

  1. LordKeiella

    LordKeiella New Member

    I am putting a Tecumseh series 1585a engine from a Toro S200 snow blower onto my tandem bike. As best as I can find, it's an 85 cc 3hp 2 stroke motor.

    The bike, loaded for touring, will be heavy. Including my 200 lbs, the bike, and the gear I plan to travel with, I expect a total weight of 425 lbs. So I need the horsepower, especially since I intend on using the engine to help me up the mountains in KY and TN! My goal is for 30mph on a flat road with power to spare for hills and such.

    I have not pulled the head yet to see, but I expect to mill the head (or block if thats the design) to raise the compression. It is a pull start and will have a centrifugal clutch, so starting is not an issue. I will have a servo motor hooked to the engine as a generator to recharge a small 12v battery so I can keep the lights, gps, cell, and laptop charged as needed.

    My big question is, what can I do to quiet the thing down! I do have a bit of reserve hp, so a muffler that quites really good at the expense of some hp is ok with me. I know a 2 stroke will never match the quietness of a 4, but there has to be some options for me.

    And, once I have some nice quiet muffler on, what are some tricks I can use to regain some of the lost power?


  2. Dobroknow

    Dobroknow New Member

    2-stroke mufflers...

    2-strokes spit so much unburnt fuel and oil out the exhaust , so any quiet muffler would eventually become saturated with oil and maybe clog .
    i've seen people make mufflers with steel wool and fiberglass mat wrapped around perforated pipe , all sealed inside a larger pipe .
    i'll be interested in how you make out .
  3. locoWelder

    locoWelder Guest

    In reality, expansion chambers are built to harness sound waves (created in the combustion process) to first suck the cylinder clean of spent gasses--and in the process, drawing fresh air/gas mixture (known as 'charge') into the chamber itself--and then stuff all the charge back into the cylinder, filling it to greater pressures than could be achieved by simply venting the exhaust port into the open atmosphere. This phenomenon was first discovered in the 1950s by Walter Kaaden, who was working at the East German company MZ. Kaaden understood that there was power in the sound waves coming from the exhaust system, and opened up a whole new field in two-stroke theory and tuning.
    An engine's exhaust port can be thought of as a sound generator. Each time the piston uncovers the exhaust port (which is cut into the side of the cylinder in two-strokes), the pulse of exhaust gases rushing out the port creates a positive pressure wave which radiates from the exhaust port. The sound will be be the same frequency as the engine is turning, that is, an engine turning at 8000 rpms generates an exhaust sound at 8000 rpms or 133 cycles a second--hence, an expansion chamber's total length is decided by the rpm the engine will reach, not displacement.
    Of course those waves don't radiate in all directions since there's a pipe attached to the port. Early two strokes had straight pipes, a simple length of tube attached to the exhaust port. This created a single "negative" wave that helped suck spent exhaust gases out of the cylinder. And since sound waves that start at the end of the pipe travel to the other end at the speed of sound, there was only a small rpm range where the negative wave's return would reach the exhaust port at a useful time: At too low of an rpm, the wave would return too soon, bouncing back out the port. And at too high of an rpm, the piston would have traveled up the cylinder far enough to close the exhaust port, again doing no good.
    Indeed, the only advantage to this crude pipe system was that it was easy to tune: You simply started with a long pipe and started cutting it off until the motor ran best at the engine speed you wanted.
    So after analyzing this cut-off straight-pipe exhaust system, tuners realized two things: First, that pressure waves could be created to help pull spent gasses out of the cylinder, and second, that the speed of these waves is more or less constant, though it's affected slightly by the temperature of the air. Higher temperatures mean that the air molecules have more energy and move faster, so sound waves move faster when the air is warmer.

    Putting a divergent cone on the end of a straight pipe lengthens the returning wave, broadening the power band and creating a rudimentary expansion chamber.

    So, to sum up, when the negative wave reaches the exhaust port at the correct time, it will pull some of the exhaust gases out the cylinder, helping the engine to scavenge its spent exhaust gas. And putting a divergent cone at the end of the straight (parallel) "head" pipe broadens the returning wave. The returning negative wave isn't as strong, but it is longer, so it is more likely to find the exhaust port open and be able to pull out the exhaust gases. As with plain, straight pipes, the total length of the pipe with a divergent cone welded on determines the timing of the return pulses and therefore the engine speed at which they are effective. The divergent cone's critical dimensions are where it starts (the distance from the exhaust port to the start of the divergent cone is called the "head" pipe), while the length of the megaphone and the rate at which it diverges from the straight pipe determine the intensity and length of the returning wave--A short pipe which diverges at a sharp angle from the head pipe gives a stronger, more straight-pipe-like pulse.
    Convergent cone. This is at the end of the belly section and reflects the pressure wave back toward the engine. The cone's taper angle influences how long the pressure wave takes to return along the tuned pipe. Again, a more pronounced taper causes a more intense pressure wave of short duration; a gentle taper results in a longer, less intense wave. A taper angle in the range of 15 to 20 degrees, or roughly double the angle of the divergent cone, is thought to be ideal.

    Stinger. This is the last part of the tuned pipe. The stinger's diameter and length are important to performance but are largely irrelevant in RC car applications. The diameter and length of the stinger are governed by most sanctioning bodies, therefore, most pipes are designed to meet these regulations, and there is less variety of stinger sizes. The ideal stinger diameter is about 60 percent of that of the header pipe, and its length should be 10 to 12 times its own diameter.I hope this helps you and not just confuses you more.
  4. Neon

    Neon Member

    Maybe not but i've heard 2-strokes that come pretty close to being quiet as a 4. The old Honda Express comes to mind there. Or most any moped or scooter out there. I've found most quiet two strokes don't clog the exhaust all that often as long as the oil mixture is right and the oil is of a good quality. Poor quality oil sure makes things carbon up in a big hurry. I'd have a look at those quiet 2-stroke exhausts and see what makes them tick and go from there.
  5. LordKeiella

    LordKeiella New Member

    I was wondering if it would benefit me to put a muffler from a newer 100cc+ scooter, after a well thought out expansion chamber. My reasons for a 100cc+ is because the muffler will be larger, more free-flowing that what would be on an 80cc. I know it will take a lot of room, but it is a tandem, so I do have space to play with to some degree.
    Also, do I kill the chances of gaining from the above mentioned expansion chamber if the exhaust pipe is curved exiting the cylinder?
    The configuration I am imagining it this:

    Engine-pipe with smooth 90 degree bend forward-straight pipe-pipe with smooth 180 degree bend (this gets me up th just behind the captains seat tube)-expansion chamber-muffler

    I understand the acoustics and wavefronts concepts of the expansion chamber, but dont know much about the details. Most of what I know is of the 4 stroke world, where these things are still important, but nothing like a 2 stroke. Do pipe bends kill the wavefronts I need for the expansion chamber to work for me? Maybe I need to go engine-short smooth 90-expansion chamber-short smooth 180-muffler, and forget about getting a 4' length of clear area to work in?
  6. professor

    professor Active Member

    My 2 cents is to forget the expansion chamber. You have 6 hp, not 3.
    A 2 stroke can be made to be quieter than a 4 stroke because there is no valve clatter to deal with.
    You silence the exhaust with OEM style mufflers - one (or better yet 2)from a small motorcycle with sound pack material inside.
    The intake tract needs to be muffled with a quieting box.
    Those Techumseh engines are very high quality. Good choice.
  7. LordKeiella

    LordKeiella New Member

    professor, 6hp?? really?? Where do you get that info from? If thats true I dont need to do ANYTHING to it for performance! It's already overkill! How sweet that will be. Man, with that kink of hp I should be able to do 20mph up the mountains in TN with no trouble and still pull down 60+ mpg! I can work on efficiency and clean instead of horsepower! I have used Amsoil 100:1 2 stroke oil for years, in everything imaginable and never had anything but great results, so I'll be using it on this engine too, tho I will run at 80:1 just as a bit of insurance. I am thinking that if I have 6hp, I will be running it at a lighter load that the 50cc engines around this forum here. In a 4 stroke, running at WOT, if the engine is loaded to an rpm where the cam and exhaust and intake all are working together, the engine will be more efficient that the same engine at half throthe, rpm's being the same, because of turbulence and pumping losses at part throttle. Is the same true for a 2 stroke?
    Any idea what a reasonable mpg might be if this engine were on a single person, flat road?

    At 6hp, the freewheel sprocket on the back rim may not take it so well, right? I may have to use a jackshaft and transfer the drive to the left side instead of the right. Hmm. New problems if it really is 6hp.
  8. professor

    professor Active Member

    The engine was rated at 6 hp by Toro.
    I had one on a field bike, running thru the rear derailer and it worked fine. Felt like six hp to me.
    To me, a rider jamming all his weight down on the pedals has a lot more force than a little engine. The shift kit guys don't seem to have any trouble with the standard sprocket drive and some of the engines are modded.
    I abandoned the project after using it in the fields- rode too hard and the narrow tires got caught in ruts a lot- no fun.
    The snowblower uses a governor. I am not sure on the max rpm.
    I actually kept the governor,so that I could not over -rev the engine by mistake.
    just used the existing spring onto a throttle cable so it would idle down (on some of the carbs you need to add a idle stop screw to be able to idle- the stock set-up has no need to idle, so it was left off).
    I still use one of these Toros at work for snow and have a couple of spare engines set aside.
    If you ever want a new snowblower, the guys at work got a new Toro 2 stroke with the aim-able shute and they love it- I got the old one.
    I know nothing about milage or efficiency on these. I do know 2 strokes have almost no torque at low speed, so the throttle is open a lot at high demand and low rpm.
  9. G-Superior

    G-Superior Member

    i have a few of those engines and they are great!
    They are also used in hoover mowers but the carb is in in the back while snowblowers are on the side of the crank case
    To make then a bit more powerful i would recomend to enlarge the exhaust port(side ways) raise compression a smal amount, clean the transfer ports to get rid of the drilling marks that they left behind at the factory(you will find 2 tranfer ports that then split into 4(2 in each side) and the exhaust has 3 ports
    Now talking about how loud it is i dont know because i never used a snowblower but over here in UK they are very quiet in the mowers(they have a really big muffler while smowblowers have small ones because the carburator is where the muffler is supossed to go!:goofy:
  10. Gungatim

    Gungatim Member

    I built a scooter using a similar motor, the 3hp version. The older ones from the '70's have the idle screw. Performance isn't great, I get 20-25mph on it, but it is loud. My pipe is probably too big, 1.25" diameter and about 30" long. I did weld some washers inside to muffle but it still sounds like a big dirtbike. I have lots of these old Toro/tecumseh 2cycles laying around, some with electric start from the deluxe snowblowers. they are fun and cheap but no low end power, good high end though...
  11. tacoshell4

    tacoshell4 Member

    how do you plan on mounting it and powering the wheel? i have one also that i havent tried to mount yet.. when i do its going in an occ stingray.