Two stroke engine simulation software.

[tomale]

All I can say is wow!! my head is swimming... what are some good books that could help me understand 2 stroke therory? Not that I am going to start porting my bikes.
by the way, Harry Taylor is still with us... and living in oregon... I do not have his phone number but if someone would like it, I do know who to talk to to get his number. email me and I will respond.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)
72'sixday (project bike)

[Ernie Phillips]

"Two Stroke Performance Tuning"  A. Graham Bell.  Good balance of theory and practice with many examples of modifications with both dyno and track results.

"The High-Performance Two-Stroke Engine" John Dixon.  Very theoretical but after reading several times, it's starting to make sense.  

"Two-stroke Tuner's Handbook" Gordon Jennings. Many consider this the Bible of 2-stroke tuning.  The material is dated but so are our old air cooled engines.

If I could just have one book, it would be Bell's.  Even if you don't want to solve equations, his many real world examples give the reader a better understanding of how changes in compression, port timing, carbs, pipes, and timing effect engine performance.

Thom, Tuning the 2-stroke engine fascinates me.  My original inquiry was about computer simulation.  As you can see from comments to this post, there are many, many variables with very few absolutes.  My thought was that if I could baseline a stock engine then do computer simulation "what-ifs," I could them pick promising configurations and test them.  I'm not seeking peak power, just better power.  "Better" to me is more area under the curve.  Look at the 100 dyno curve.  I'd be happy to knock 2BHP off the peak and change it for +2BHP beginning at about 5K with good over-rev potential.  The dyno chart shown indicates peak at 8300RPM and is dead at 8800RPM.  If the motor likes to over-rev, you can avoid a couple of shifts.  And, with the Sachs motor, less shifting is always better.  Even with a stock engine, I'm not getting passed on the straights.  If not geared correctly or in the wrong gear, I do lose time coming out of turns.  In Cross Country, many times I have to down shift an extra gear or abuse the clutch to get going.    This cost time and energy.  So, a perfect small bore engine to me, is more meat in the middle, but will also rev to the moon.


Ernie P.
Chattanooga, TN

[john durrill]

Ernie,
 I'm sorry. I saw a picture on ebay of a D sleeve and thought it was one Donny had made. That one did use a bridge in the intake.
You and Nelson may be right on the exhaust lips as a compromise for cost done buy Sachs.
 The Sachs Alloy cylinders were made up by another company to Sachs specs,  Mahle ?. Its hard for me to believe that they would not have changed the specs to get a better port design though. There are several reasons why i am thinking this.
 Sachs used expensive main bearings , tapered roller bearing on the counter shaft , tapered the rod pin on the big end , quality forged pistons and rings excellent steel in all the components. The odd shaped header pipe on the iron barrels was done for some reason and it looks like they carried it over to the alloy cylinder,  just cast into the cylinder instead of head pipe shape. Carl didnt offer opening up the port to round in his hop up sheet. I would think that would be an easy change if it helped. Maybe the pipe had to be designed with the shape change in mind?
 I know from a past experience with a  175 cc Kawie factory hop up Kit ( cylinder , head , pipe and carb. ) that a lip positioned in the right location in the exhaust port can make a big difference in power.
 I dont know the how or the why Kawie engineers did that but it did work .
 Maybe the pipe used dictates what works? Monark used a different pipe than Penton and Carls pipe is different from both of the others.
 I am Fishing for more insight in the effect that the lips could have over a port blended from the window shape to the pipe ID over its length.
 I think to increase the power you have now over the the same rpm range and stay piston port, increasing port width safely ,blue printing the engine, stuffing the crank case and bumping the compression with in limits will give you all you can get. Ron,  Nelson ,  am i right?
  Carls specs should be safe . Maybe not quite that wide on the exhaust for the 100 ?
 Adding boost ports the right shape would help. Get more flow into the cylinder. Big T cylinder Ernie?
  A reed with added boost ports would work well to give you the most intake duration, and cylinder filling possible. Its a big step though. A pipe change would get more from the reed and boost ports . Reed engines seem to like a different pipe design.
 I have a spec sheet for a Zundapp Reed kited cylinder modification we can send. Its a 54 x 54 mm engine and it should work well on the Sachs engine.
 Speedy modified and rode some Zundapp engines with the reed added ( not as wild in the ports specs shown ) and liked what it did .
 You could ask him about the kit.
You saved me several hours on Sat. Ernie .
Thanks .
 We were going to glass bead a stock cylinder , manifold and take some pictures to post. You casting latex saved me a bunch of time.
John D.
 
 
 

[brian kirby]

On a possibly related note, I know V8 race engines use rectangular intake tracts because they are better than round. I dont know if its velocity or total flow that is better, but rectangular was better in some from than round. The rectangular section of the exhaust could be intentional for those same reasons, but that is just a guess.

Brian

'73 Berkshire

[linglewn]

John,
The mods you mentioned should be safe and provide some improvement. I would never say that you have gotten "all you can get." There is always a combination that may be better-you just have to find it.

Nelson Lingle
73 Jackpiner
71 DKW 125

[john durrill]

Sorry Nelson,
 That was a poor choice of words. I did mean with a good chance of success and with out loosing reliability. If we had new, current production parts availability then I would be a lot more willing to try things just to see how they worked. I bet Ernie is caught in the same dilemma . Its one reason i ask so many questions .
 Thank you for your time and help
John D.

[rob w]

quote:Originally posted by john durrill

Could you folks go into the advantages and disadvantages........
Open up the exhaust exit to a full circle. (As in #2)

John, Makes sense to me that this would help performance some.
This was done in one operation on a mill, using a tapered end mill. The guy I bought the cylinder from
in Chicago, did it. I asked him for the end mill also, but he could'nt find it at the time.
(that was a couple years ago) I'm going to locate another tapered end mill and have a set-up to do this.
One advantage in milling it this way instead of grinding, is that it remains consistant each and every time.
I wished I had cleaned the cyl. before I shot the pics.
Chuckle
Bob W

[john durrill]

Ernie,
 Here is the Zundapp reed spec's. Speedy could give you a clearer copy but the 30 Deg on the added port is pretty standard. I like the V type ports over the single rear port from fooling with no so Rabid Rodent engines. I " Think " it scavenges the combustion chamber better.  We used Pabatco's specs for the kit. 2 extra holes higher in the piston will cool the piston crown down a lot better.



Here are 2 pictures of a Sachs cylinder that was reed kitted.
We cant see if boost ports were added but it would be the only way to get all the value from the mod.


I would have added 2 more 1/2 inch holes on this kit for cooling


If you  use some thought on port width and placement this will allow you to make more power over the entire stock 100 power band.
Pick the right reed petals, port widths , placement and engine reliability should be good.
We did this to several Rodents back when and most were used as dual purpose bikes. Transportation to and from school and trail riding.
They gave many miles of good service to the owners. The reeds lasted  hundreds of miles.
 We had 2 100 Rodents Reeded with 24 , 26 mm carbs and they were  as reliable as stock engines. The wife and I both loved them on the trails.

John D.

[john durrill]

Bob,
 That's a good picture. Shows the amount of metal to be removed well.
 Thank you.
 I think the only way we will know for sure on what it does to a stock Six-Day power band is for someone to have a cylinder setup working and jetted right, then do the mod and test it. It would be good to know what only that change did  before cutting a cylinder.
 If it shifts the power up in RPM only that was not what Ernie said he was looking for.
 If we were not in the middle of restoring another bike now we would try it.
 John D.
 

[Ernie Phillips]

Bob,  Glad to have you join the discussion.  Let us know if you build an engine with that cylinder.

John,  Thanks for the Zundapp info.  Although the reed valve has done wonders for the two-stroke, they are not allowed in AHRMA Classic machines.

The more I read, the more I study others efforts, the more uncertain I am about how best to improve the Sachs engine for my purposes.  Good thing that the STOCK configuration works so well.

Ernie P.
Chattanooga, TN

[john durrill]

Ernie,
 You can use it in the 100 class that's why i mentioned it chuckle chuckle!
John i agree with you on stock is best for most things D.

[Ernie Phillips]

John,  I forgot about 100 being Sportsman and "reed" legal.  Something to think about ... Thanks  -EP