Two Stroke versus Four Stroke

Discussion in 'Performance Mods' started by roughrider, Jan 14, 2013.

  1. roughrider

    roughrider Member

    I do not wish to re-ignite the old debate…

    Well, er, maybe I do.

    The fact is, I decided to go with a 2 stroke for my first build, and that is despite my first impulse—a four stroke. So I'm a four stroke guy who's converted.

    Here's why: 1, I just can't STAND the idea of how wide 4 stroke builds come out. I'm coming from a bicyclist's background, so width and weight are REALLY IMPORTANT! 2, contrary to the buzz, reliability is a function of the mechanic and the rider, not the engine. The deep study I have made of these Chinese 2 strokes has convinced me I can handle anything that goes wrong with them; more, I can make considerable improvements. I do not have that confidence with any of the 4 strokes. 3, the 2 stroke China Girls look really cool. The 4 strokes look… well, OK in the better builds, but only that. They don't just TOTALLY suck in the looks department. 4, CC for CC, two strokes just make more power with less weight. It's that simple. Facts talk, and BS walks.

    But one selling point for the Chinese two strokes is that they are cheaper. That does not fly. By the time I was done ordering the mods and accessories, I'd spent just as much money as a basic four stroke kit.

    But I ended up with a QUALITY 2 stroke kit rather than a cheapo 4 stroke build. First, I ordered a "Flaming Horse" from I wanted the kind that had the straight up and down spark plug, not the "slant." This accords with my understanding of the place the spark needs to be to get the proper fire. I got a 415 chain. I bought a spare muffler so I can experiment with an extension and various mods; plus, I've noticed that a lot of people have exhaust failures from engine vibrations. I also ordered a Jaguar CDI kit (which includes a hotter coil) and the NGK iridium plug. On top of that, I got a Sick Bike Parts engine hardware kit. The enginesonline stuff, with tax and shipping came out to just under $250.00. The Jag CDI kit was ~$75.00. Another ten (with shipping) for the plug, and fifteen for the SBP stuff brought the total up to $350.00. ALL that was with tax and shipping, of course. Real costs, not just advertised prices. Not cheap! Even so, I'm got the DELUXE 2 stroke kit (black, no less, with Allen head hardware, and quite a few spare parts) for the price of the CHEAPEST 4 stroke kit. But who knows what my additional costs will be?

    I'm looking to do a Jaguar inspired series of tests for more bottom end torque. I don't really care about top speed. I need a torquey beast for pulling a trailer with camping gear in the mountains. Unladen, in the flats, I'd prefer a stoplight jumper. I'm gonna do intake and exhaust extensions for starters, starting with bone stock, followed by a series of cheap mods and tests. I won't even fire the engine up until I've broken it down and inspected every detail. (The enginesonline specs say that their motors already have good bearings and wrist pins. We'll see.)

    So that's my first build design theory. This is all going onto a Schwinn bomber style frame, the only stock item being the frame. In another post, I'll put up the pix of the build. In the meantime I wait, impatiently.

    With respect,
    Last edited: Jan 14, 2013

  2. Fabian

    Fabian Well-Known Member

    Then you will need a Rock Solid Engines reed valve intake and a CR Machine Man twin spark plug cylinder head, not because it has twin spark plugs but because it has the biggest cooling surface area of any of the billet cylinder heads out there.

    This is my heavy haul setup and it's set up to haul, though my next door neighbour gives me a hand on the mountain climbs:

    Last edited: Jan 14, 2013
  3. Fabian

    Fabian Well-Known Member

    Just about all of the Chinese 2-stroke Chinese bicycle engines come with the newer crowded roller big end connecting rod bearing, which has proven to be almost bullet proof for reliability and with the Jaguar CDI, you can expect to have excellent reliability and engine life.
    The 4-stroke engines look like you've bolted some hideously ugly and ungainly large and clumbsy rototiller/rotary hoe engine on your bike - they look plain terrible and ugly as sin.

    Mention must be made that it costs around $50 and takes 10 minutes to disassemble and reassemble a complete top end on a Chinese 2-stroke engine, and they are good for about 4,000 kilometers at high duty cycle.
  4. Richard H.

    Richard H. Member

    Tired, old debate. Whatever.....just keep it legal and you're okay.
  5. roughrider

    roughrider Member

    I have been wondering about the head, actually. I'll be installing a heat sensor. I won't be increasing the compression at first because I want to test and compare, doing mods bit by bit, carefully and patiently. A good part of the fun for me is the whole research process, and one thing I really like about these 2 strokes is that they lend themselves to tuning mods.

    Great photo! Made me laugh.

    (Also, I sent you a PM regarding your trailer recommendations, but it was bounced. The error given was that you had exceeded your storage limits. You might want to look into that?)

  6. roughrider

    roughrider Member


    I was being tongue in cheek. :jester: I'm not really interested in the same old debate either! I have noticed that there is some real innovation happening in high tech two strokes in the world though. One suspects a comeback is under way.
  7. grinningremlin

    grinningremlin Active Member

    Was that "tired and old debate" or "I'm too tired and old to debate"?Fabian, is that a pic of you?Nice set up, I thought the semis in Montana hauling three and four trailers were crazy.Personally I prefer 4 stroke, low end torque, ease of starting and low noise are the winners.
  8. Fabian

    Fabian Well-Known Member

    Yes, that's me in the photo. I'm on the Alpha prime mover and my next door neighbour is riding the Omega prime mover in heavy haul configuration.
  9. roughrider

    roughrider Member

    Apples and Oranges

    I like both. I'd just hate to have to pick one over the other. It is not, to use a trendy aphorism, a "zero sum game." Picking a two stroke does not mean I won't use a four stroke.

    Shoot, one of my other projects is an 82 Yamaha Virago 750. I'm doing a cafe racer with it. The monocoque frame and mono-shock were hidden by this lame-ass "chopper" look. Underneath, was a race bred, awesome machine with that bubbah-dah bubbah-dah super reliable V-Twin.

    Seriously, anyone who does not like the sound of a big twin four stroke is, well, er, fracking insane. And while we are on the subject of sound, do not Harleys rule?

    So yeah, man, I like the sound of four strokes. And I basically just hate the sound of two strokes. It is not the volume. It's the pitch. I'm not a fan of violins or lead guitars either. I like the bass, the bassoon, the trombone, and the cello. But that's just an aesthetic opinion; like any digestive exit orifice, opinions all stink.

    Just being honest.

    I had to get over that to even consider a two stroke build. However, a little research showed how to quiet down the screeching pitches. Sonic amplitude does NOT equal power.

    All that being said, I guess what I'm getting at is that I'm super sensitive to sound. Part of my project is to get better bass and less treble out of my build. This forum has proven to be a grand resource for that. In this post, I avoid any technical details, but I think I got a handle on getting a good bass tone out of a two-stroke.

    Last edited: Jan 14, 2013
  10. Fabian

    Fabian Well-Known Member

    An easy way to quieten down a 2 stroke to almost silent exhaust levels is to attach 2.5 feet of high temperature soft silicone hose. The soft silicone absorbs noise tremendously well and under full throttle i can only hear intake noise.

    Yes, we all like the sound of a 90 degree V-twin 4-stroke but unfortunately motorized bicycle engines are not made in a 100cc V-twin configuration that can be attached to a SickBikeparts shift kit.
    If it was, i would have a small V-twin 4-stroke and SBP shift kit attached to my bike tomorrow, so long as it didn't look like a rortiller/rotary hoe engine.

    I'd be equally happy with an 80cc boxer twin cylinder 2-stroke bicycle engine that could be attached to the SBP shift kit - It would be almost vibration free by design.
  11. roughrider

    roughrider Member

    Yeah man! Boxers are just engineering marvels. Harleys may sound bad ass, but that BMW purr is every bit as cool.

    Thanks for the tip on the exhaust extension. I'm already on that like white on rice. But when you say, "high temperature soft silicone hose," what IS that? Heater hose? Like we use in car engine cooling systems? I'd like to source that, but I'm not sure what to use.
  12. Fabian

    Fabian Well-Known Member

  13. roughrider

    roughrider Member

    Thanks for that. I see those guys only sell in large quantities, but that gave me the info I needed to identify the type of hose that can handle ~500° F. A bit of googling showed that there are hoses available in shorter lengths used in applications like coffee and beer makers. Also I see that you attached the hose at the tip of the muffler. I was planning on doing a splice just before the muffler with my fingers crossed that the temp of the metal would have gotten into acceptable margins by that point. So you're getting peak temps of maybe 350°F at that point. (Maybe?) I haven't found any detailed EGT analyses along the length of the exhaust systems for these engines, so I'm going by generic data--figuring a temp of about 700° F about an inch from the port and dropping off rapidly after that.

    I've already designed a test using welder's crayons to mark strategic spots on the exhaust system, btw. I've heard of using paint with known burn temps too. (Bear in mind, I'm more concerned with the temp of the metal than the EGTs, though the two are related, of course.)

    Last, that's one heck of a bike! I can see layers of years of trial and error tinkering in the design.

    ... OK. That was not the last thing. Here's the last thing. All my parts shipped yesterday. They should be trickling in over the next few days. I've been talking a lot, but I haven't shown anyone any pix of the bike I'm working on.

    Last edited by a moderator: Dec 18, 2015
  14. Fabian

    Fabian Well-Known Member

    My bike is fitted with a Koso EGT gauge and the exhaust temperature fluctuates between 650 and 850 degrees Fahrenheit, between cruise and the engine working it's guts out over long periods of wide open throttle at low speed and low airflow over the engine.

    The silicone hose fitted to my bike is rated somewhere around 500 degrees Fahrenheit but in over 4 months of use with over spec temperatures, the silicone remains in good condition; maintaining it's soft and pliable characteristics.
    I have no issues with replacing the hose every 6 months, or however long it takes for the silicone to degrade and require replacement.
  15. Fabian

    Fabian Well-Known Member

    Absolutely spot on. It's been three years of trial and error and tinkering in the design, and i'm still adding improvements and new and more efficient components to the bike.

    By the time the project is complete it will be a 5 year assignment in maintaining my patience and sanity as well as the bike trashing a few relationships along the way, but lets face the cold hard reality of life: women come and go (usually with a huge tantrum) but the bike will always be there in the morning :banana:
  16. roughrider

    roughrider Member

    OK. So my guesstimates were right in the ballpark. I found several suppliers of high temp hose in various colors. Where is is the EGT sensor located? Fairly near the port? I can't see it in the pic. Also, what is the diameter of the pipe, and the tip, if different? (Haven't got my stuff yet, so can't measure.)

    Yeppers. One of sisters once told me that I needed to let a women know right at the beginning that I was intensely devoted to my art work, so if she ever got jealous and tried to fight that, she would lose. It may seem cold, but in fact, that policy has worked out. Any good woman can handle that. My break-ups have been over other things. Lately, I've been preferring to just have some really cool female friends with occasional benefits. :cool:
  17. Fabian

    Fabian Well-Known Member

    Do a Google search for "Bike Build as of March 2012" and scroll down to No 38 and you will see photos detailing the Exhaust Gas Temperature gauge and how it is set up on the bike.
    Sparks2056 likes this.
  18. Fabian

    Fabian Well-Known Member

    You will need 1/2 inch internal diameter high temperature silicone hose with a length of 2 1/2 feet to replicate my setup.

    Remove the end of the muffler and cut off the internal metal tube, leaving about 2 inches protruding. Take the tubing that's been cut off and cut out 2 sections of 2 inch (length) tube as you will need these to be inserted 1 inch inside each end of the silicone hose so you can zip tie the hose to the frame without deforming it and restricting exhaust flow.

    Make sure you have generous radiuses as the hose exits the muffler tip and into the 2 inch metal tube sections that will be tied to the frame. You don't want the silicone tube to collapse in on itself as it enters the metal tubing.

  19. roughrider

    roughrider Member

    Found it. I see the gauge is mounted at the top of the muffler. I was not expecting temps so hot, that far from the port. Wow.

    Now, I heard this from another mechanic. He said you want the gauge at the hottest point, so he'd paint this stripe of engine paint on the pipe, and put the gauge where the paint first burned through. I thought that was pretty clever.

    Great page, btw. Nice to see the big list of all your mods.

    But yikes! Overwhelming. So... one thing at a time, one thing at a time. And thanks for the data on attaching the hose.
  20. Fabian

    Fabian Well-Known Member

    The literature that comes with the Koso Exhaust gas temperature gauge says to insert the probe 6 inches from the exhaust port. Because of the length of the probe, you cannot mount it on the small diameter of the exhaust pipe.
    As things are, mounting the probe at the top of the muffler comes to about 9 inches, so that's good enough for me.. Also, when you place the probe in it's fixed position, the tip of the probe sits in the exact centre of the main exhaust flow from the small diameter of the exhaust pipe, and that's where you want it to be.