Bimotion. Two Stroke Engine Simulation 2t ((FREE))

Other Available Pipe Design Programs & Why I Think They Are Lacking

MOTA for $175

1) Here's another persons comparison between ECcalc and MOTA: Click here.

2) I know a guy in Australia who races a kart with a KTM SX250 engine in it and he has his own dyno and makes his own pipes. He told me he built an optimized pipe designed by the Mota software and it didn't give him good power.

3) A friend of mine put the Maico AW250 engine details into Mota with theoretical pipe details and gave me the same details to put into ECcalc to compare the two results. The Mota waves didn't change from single to triple cone diffuser. At least the diffuser wave should change but it didn't so Mota doesn't use the detailed wave generation method that I use, otherwise the wave peak would be more to the left with a single cone diffuser.ECcalc says the diffuser wave should start at 1.65ms using 564 degrees C mid header temp (@ 5800RPM), and 1.7ms using 514 degrees (which is what ECcalc calculates it would be close to) but Mota shows 1.83ms. Mota shows a high baffle wave peak but the contrary 2nd generation diffuser wave overlaps it which would lower the peak but Mota doesn't show that lowering. Blairs papers show that the secondary diffuser waves are 1/4 the time duration of the primary diffuser wave but Mota makes them 3/4 the time. My conclusion is that Mota is fancy software but they lack the precision that ECcalc has.

Also a person who has Mota says there is no place to enter the exhaust gas temperature which means it provides only a rough estimate which is OK when using a simulator without the secondary waves but when including the secondary waves (as Mota and ECcalc does) it's best to truly know what the temp is.

Bimotion for $249

It is an Excel spreadsheet program for designing pipes. They admit on their site that they use Blairs formulas in the book "Design & Simulation of two-stroke engines". Unfortunately not even Blair, way back then (>23 yrs) , was very accurate at simulating the return waves. Here is an example of his simulation from one of his research papers, the one on his dyno. Notice how the calculated wave (thin line) lacks the pressure dip before TC that is caused in this example by the negative pressure 2D and 1B1D secondary waves.

2 Stroke Wizard for $27

I had bought this program before starting on making ECcalc and it just wasn't very good at designing a good pipe. And when my hard disk crashed I asked them to send it to me again to replace the lost program and they wouldn't even reply to my email ! This program only uses Blairs formulas which are childs play compared to properly simulating the return waves and calculating the power depending on them.

Crappy free programs

Some programs are even based on the formulas proposed by Gordon Jennings from way back in the early 70's. Man they were just beginning to investigate back then. Basically they knew next to nothing.

Jennings main shortcomings;

0. He assumes the same temperature and sound wave speed inside all pipes.

1. Because of his temperature error his calculations for the tuned length were off by 3.5" compared to a Maico 440 pipe, and 1.75" compared to a Maico 250 pipe. (both pipe specs along with full engine data, horsepower data, and EGT were given to me for analysis.)

2. He uses formulas to calculate everything but belly length, letting it take up the remaining distance. This is totally wrong because the belly length should be set to allow a slight overlap of the diffuser and baffle waves. That set length is optimally almost always below 4" (100mm).

3. He had no idea whatsoever about the return waves the exhaust pulse causes, their return time or their time duration. His ideology was not based on the reality of what was happening inside the pipe but just on scant trial and error data.

4. He calculates the header length as a multiple of its diameter. It's correct length is that which locates the secondary waves in correct relation to exhaust closing time at top RPM.

5. He calculates the belly diameter as a multiple of the header diameter although the header can be too narrow or too wide. Proper sizing depends on the exhaust pulse pressure.

6. He calculates the stinger diameter as a fraction of the header diameter whereas it should be calculated by the exhaust pulse pressure.

7. He calculates the stinger length as a multiple of its diameter whereas in reality the same back pressure can be had by a fat long stinger as by a skinny short stinger.

8. He recommends not going over a combined baffle angle of 30 degrees (15 from centerline) although many successful pipes use much larger angles. According to physics there is no limit to the angle. It's just that the shorter the baffle, the shorter its return wave. The return wave length should match the RPM, the timing between transfers closing and exhaust closing, and the desired RPM spread of the power band. And its length is dependent on the length of the exhaust pulse.

9. He was calculating for a single coned diffuser which gives weak results compared to a multi-coned diffuser of gradually increasing angles.

10. He calculated for a 2 to 1 ratio of angles between the baffle and diffuser which is too limiting. Any way when you go to a multi-coned diffuser there is no single angle of overwhelming importance to compare the baffle angle to. So in modern pipes there is no ratio formula.

Well he was a pioneer 46 years ago but anyone who uses his formulas now is way behind the times. We have progressed so much farther than his formulas and now have computers to simplify the complex process. (But thank you Gordon for helping along pipe research in the early days. RIP)

At a certain online pipe calculatorI entered specs for an engine reving to 10,000 RPM and only changed the area for the exhaust port to get four different pipes. You can seehow the timing is different for each one as evidenced by the differenttotal lengths till the baffle cone. That is a disaster because the needed wave timing to match the ports timing would remain almost the same but they changed it drastically on each pipe, evidenced by changing their lengths. Here's howthe program works: It makes the header diameter according to theexhaust port size, then the belly diameter according to the headerdiameter, then the baffle and diffuser angles (at a 2:1 ratio)according to the desired exhaust temperature which remained the samefor all four pipes. Its emphasis was on areas, not timings. All 4 pipes have different tuned lengths (to the start of the baffle wave) and 3 of them didn't even have a belly which is needed to separate the diffuser and baffle waves so that your're not wasting energy by letting then cancel each other out where they cross (since they are of opposite pressure). And it designed only single cone diffusers which are ineffective compared to 3 cone diffusers.

Man this is when i wish i could afford some of the software out there... i could run simulations of several different heads in an afternoon and determine the best design without even touching the engine!

Bimotion. Two Stroke Engine Simulation 2t

Download File 🔥 https://cinurl.com/2y1G53 🔥

Twostroke are the most complicated engines to understand, even with only two moving parts. Sometime they'll just blow all the theory out of the water. Example KTM 125 had the most power anyone ever saw out of stock 125. Look inside and you had to scratch your head. Worst transfer case/cylinder mismatch of any of the motor. Port height were all over the place, left higher than right or vise versa. Yet they made big numbers, and "fixing" the problems didn't make much if any difference. Some of the Rotax watercraft motors. Port timing and time/area that would make them super high strung rpm motors, but they didn't run like that at all, and were hard to improve on with all the usual mods. Type 693 rotax motors with real low port heights and time-area, Software shows they'd only make 100- 110hp at low rpms, but they pull 120 all day long at higher than predicted rpms. crappy head, loose pipe (1 pipe for two cylinders).

Harris, thanks for the info on the CR125... i am defintiely interested in this sort of detail! If you have any more info like this id love to know whatever you can pass my way! In fact i might try to start another thread where we can compile known data on 2 stroke engines like you provided and like what i have found with my CR250. I wish i had moto814, etc on the other end of the phone to take advice from! That sure is a huge help to have guys with that level of knowledge at your disposal.

A 2-stroke engine has one thing that sets it apart from its 4-stroke cousins and that is the effect of temperature. It has much larger effects on the 2-stroke engine performance as the engine depends to a large degree on the wave action in the pipes. The wave speed in the pipes is a direct function of the gas temperature. The higher the temperature the faster the wave speed. We use this effect to get good overrun performance - leaning the mixture and/or retarding the timing slows the combustion process down resulting in less expansion work in the engine and higher pipe temperature which in turn results in more overrun. It is important for the simulator to accurately capture this effect. This is done mostly with the combustion model. They are from simplistic to sophisticated as follows: be457b7860