Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Automotive A turbocharged two-stroke

  1. Feb 20, 2005 #1
    How would you go about designing a turbocharger for a small 62 cc two stroke engine. I have heard of two stroke snowmobiles being turboed, and i understand the concept of a turbo well so it seems plausible.

    Bolt a small turbo in the passage of the exhaust port, then somehow have it turn a turbine on the intake side. would this turbine be before or after the air/fuel mixture? Also, the exhaust port and intake port on the complete opposite sides of the engine, so... :confused: plus how would you tune a carb to a turbo?
  2. jcsd
  3. Feb 20, 2005 #2
    Possible but difficult; on a 2-stroke, the exhaust port is open while the fuel-air mixture is forced into the cylinder. With a turbo you would blow a lot of the new charge out the exhaust pipe. Besides the horrendous fuel consumption there would be little pressure increase and HP gain. The exhaust could be tuned to provide an immense amount of backpressure enabling use of the more dense charge, but the engine would only run well within a very small RPM range.

    Adding fuel injection and an exhaust valve I think would be the more feasible method. Of course that would cost several thousand dollars to do. Where you mount the turbo is the least of the problems.

    If I recall, some folks in Australia are working on it.

  4. Feb 25, 2005 #3
    link to the aussies?
  5. Feb 25, 2005 #4
    Here you are:

    http://www.banksiafdn.com/page_assets/Case2003_Orbital.pdf [Broken]
    Last edited by a moderator: May 1, 2017
  6. Feb 26, 2005 #5


    User Avatar
    Science Advisor

    Awesome link Geniere! Not sure how they keep the engine lubricated but now its similar to a 2 cycle diesel where the exhaust port timing and backpressure would not be as critical but still need to be managed for the turbo to work optimally. Maybe more along the lines of a Miller cycle camshaft for 4 cycle turbo applications.
  7. Feb 26, 2005 #6
    Yeah- How do they lube it? I think piston engine developement is about a far as it can go except for small incremental improvements. We need the chemists to come up with a super oxidizer to mix with the fuel at point of injection. Mayby like the German's T-Stoff and C-Stoff. Perfectly safe at 500 meters. :biggrin:
  8. Jan 31, 2009 #7
    Although this may sound wrong at first the exhaust pipe in a two stroke engine actually functions as if it is a cam shaft. In other words the shapes and length of the exhaust pipe will control the flow of the exhaust gas which in itself places some control over the intake mixture. Therefore a turbo charger will severely mess up a two stroke with the exception of some large diesel two stroke engines with limited power ranges.
    But what can be done is a super charger! The basics involve a multi cylinder two stroke engine as one intake port really needs to be open at all times. It also helps to have a large intake air chamber after the blower so that the intake can be regular and smooth. You will also need a really good electronic fuel injection system as well as a custom ignition system.
    But after you spend a fortune the question of why will leap out at you. Two strokes can be built to make more power than you would ever want to use without super chargers. Further what power they do make can be made really suddenly. Anyone who ever operated the old Kawasaki H2 750 three cylinder two stroke can tell you that the acceleration from zero to 100 mph was insane. If one wanted a straight six could be built by joining two of those engines in line. And you can easily drill them out to take larger pistons and racing crankshafts are still in the wild for these beasts. Such an engine would be about the same length as a four cylinder in most small cars. With full race expansion chambers people will hear you coming for several miles. I know first hand.
  9. Mar 2, 2010 #8
    I once turboed a lambretta 80cc scooter.I used a small european ford turbo a friend had sittin in a junker on his lot.Its hard to discribe.It sucked & scared the heck outta me at the same time!! the amount of time it took for the turbo to spool seemed like for ever.But when it finaly hit boost levels,that little scooter thought it was herculese.I wore holes in my boot toes when it stood straight up at 50 mph.I didnt think it was gonna do anything.It was about 1,000 rpm short of its stock redline and then, Blastoff!! I thought I was gonna die.It lasted a week before it turned to schrapnel.I really never got to know how fast it could go cause it took so long for the turbo to spool.I believe if you could find a tubbo small enough,it would spool up much faster and would have better results than I did.Also,you would need a long intake manifold between the turbo and intake.It helps store boost pressure for a broarder powerband with a large turbo that dosent spool so fast.Another thing is 2 strokers are horrible @ making boost pressure at lower rpms.Too much duration during the scavenge cycle.The faster the piston opens & closes the ports the faster the boost pressure builds.
    Speaking of kawasaki h2s.I have several.2 will be turned into a v6 arangement with a shorter stroke crank,Direct fuel injection & a crank driven super charger. Weeee!!!
  10. Mar 2, 2010 #9
    You have 2 systems that work with carbs,draw through wich the the carb is placed on the intake scroll of the turbo.This system is good because it it keeps temperatures of the intake charge lower because the turbo sucks air and fuel charge through the turbo keeping things cooler.The down side is maintaining consistant air fuel ratio as boost increases.As boost pressure increases the fuel mixture gets leaner wich means you have to jet or adjust your carb for the rpm & boost pressure your going to run at. Blow through is a little better at this because you can use a carb with a float bowl and pressureize it by pluming the float bowl vent into the pipe or air box going onto the front of the carb after the turbo.The down side to this is hotter intake temps,Its a long trial and error process getting the float level height set correctly.
  11. May 18, 2010 #10
  12. May 19, 2010 #11
    Thank you.thats just what i was thinkin for my v6 h2.Im movin a little tward a whipple charger.thay are a little more efficient,compact & lower air charge temps. making the cases and crank will be fun.
  13. May 19, 2010 #12


    User Avatar
    Gold Member

    Yes, you'd be better off using a "supercharger" as opposed to a "turbocharger." There are two principle concerns (both of which have been mentioned here) with regards to turbocharger operation:

    • exhaust flow volume
    • oiling of the turbo bearings

    Quite frankly, with a small two-stroke engine you just won't make enough gas to spin the turbine wheel enough to get the impeller up to speed. Yes, you could size your turbo to match, but then you're talking about tiny amounts of compression... fractions of a pound per square inch.

    All turbos require external lubrication. Either for a journal bearing or ball bearing.

    A supercharger, however, can be made with sealed lubricant gear boxes and does not rely on exhaust flow for operation. A roots-style would probably work fine. It is essentially two meshed helices.
  14. Nov 21, 2010 #13
    Ive always wanted to turbo charge a two stroke but as it seems the way to go is Supercharging! I have a Suzuki T350 Twin which i intend to supercharge! Would it work if I was to modify one cylinder into a Supercharger and use it to boost the other would this work.
  15. Nov 22, 2010 #14
    Assuming this is a G62 mounted in some sort of large scale airplane, the real issue is power gained vs increased weight.

    A vane style (like an air-tool, die grinder, impact, etc.) super charger, is another avenue, and well suited for a two-stroke.

    To minimize charge loss, reduce the width of the exhaust port, exhaust tract diameter, decrease T1 port duration, and increase the negative T1 port angles.

    But in my opinion, converting the engine to a rotary-valve induction, combined with an exhaust system that only scavenges would be better.
    Last edited: Nov 22, 2010
  16. Jan 9, 2011 #15
    Turbo charging a two cycle is out of the question. The exhaust needs to remain unrestricted in order for the chamber to clear effectively and even then a turbo is not going to pressurize the chambers enough to produce significant power gain versus the weight gan.

    Super charging MAY seem like a good alternative, howver you're going to end up with a crappy power band at about 3-4000 rpms., which is OK for diesels who need good torque but not horsepower, after that it will crap out since superchargers gear exponentially, i.e. more acceleration=more boost. More boost equals wasted energy since you have to remember that the exhaust port is open at BDC, all your extra boost just goes out your tailpipe.

    On the other hand, and I'm not self promoting here, (ok maybe I am a little), I have devised a way to provide the right amount of boost without wasting energy in the end. It will scavenge the CC and remove most exhaust (you need SOME backpressure from the exhaust) and also pressurize the cylinder more so than what the normal two cycle crankcase can pressurize it.

    I can't go into any more details than that since I have a patent pending on this design. Suffice what I am saying into a 200 HP engine you can carry around with one hand!!

    If you wish to help on this project, please feel free to contact me. I need all the help I can get, but trust me, I am not a greedy person, anyone that wishes to contribute and help (not necessarily money wise)
    I will reward 10 fold, and that is a promise.
  17. Jan 9, 2011 #16
  18. Jan 9, 2011 #17
    Reducing charge lost by reducing the width of the exhaust port will create a smelly bomb. How would fresh air enter if there is burnt gas in there? And then you have to deal with the soot accumulation inside the cylinder which would build up quickly. There are far many variables other than what kind of turbo/super to use. You must consider how the fuel/air mixture will be introduced, HOW the exhaust will excape BEFORE the fresh air begins to enter, and the HOW to keep that pressurized air before the piston is returning to TDC. Any type of mechanical means of induction that relies on the mechanical motion of the engine will fail bar none. Except in the case of diesels
  19. Jan 9, 2011 #18
    No, you'd fracture your connecting rod since one chamber is producing significantly more power than the other. The non-charged cylinder wouldn't keep up and either burn out altogether or most likely throw a rod if not entirely fracturing your connecting rod. This doen't mean some bonehead hasn't tried it and had some succes with it, but give it time, he won't be enjoying it for very long.
  20. Jan 9, 2011 #19
    This design defeats the entire purpose of two cycles. Yes it does have only two actually cycles, however your relying on FOUR stroke technology to do that!! Why do you thnk that 4 strokes limit at about 6-8000 RPM? Because of valves. It takes energy to move those valves, and those valves move at the same rate regardless of engine speed. The original designs of two cycles had it right the first time, however EFI wasn't available at the time. Valves not only waste energy, cant' vary timing, but as wear happens the timing gets effed. This diagram was ridiculously simplistic.
  21. Jan 9, 2011 #20
    The turbines on both the exhaust and intake side are connected directly. You'd have to route a hose from the intake side of the turbo to the intake. Any snowmobiles that were turboed were most likely 4 cylinders (aka wastes of flesh). Even with a supercharger you're are going to waste as much boost as it creates so it is pointless.

    IF you used a turbine, it would be placed b4 the air/fuel mixture, since it's the flow of air that determines how much fuel to send. Better yet, just get EFI. The comp. will monitor the air coming via the mass airflow sensor and automatically adjust ignition timing as well as the fuel mixture. Like I said tho, all that boost is just going out the exhaust tho.

    If this is something that REALLY interests you I have a two cycle design that deals with all these problems, so if you know of anyone that might like to help develop this, I am not a greedy person and would be willing to have all the help possible.

    BTW, engines that have valves ARE NOT TRUE TWO CYCLE!!!!!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook