Two stroke engine simulation software.

[Ernie Phillips]

Seen at Zink 2008 RR but think it originated in TEXAS.


Ernie P.
Chattanooga, TN

[firstturn]

To all;
  Where I am going is we have such a great amount of wealth in the POG Mambers.  I feel that Ernie has started a great thread that should encourage us to help the racers within this group and/or people that are racing Pentons with assistance in tuning and developing there Pentons.
  One thing that I have said and will continue to say, a nicely blueprinted Sachs engine with a rider in top shape is the best ammo against all comers.  Just ask the Master Doug Wilford.  Doug has been there with the Worlds Best and is still the Go To Man on Sachs and how to win at racing.  I will have to say [8D] that Doug and I spar on engine setups, but I ALWAYS listen.  
  So where do we go from here.....I think Ernie should keep us posted on his racing and we as a group should make sure we help with input when we can.  When you find an exotic cylinder that you don't understand the porting bring it with to Mid Ohio or a race and let Ernie look at it and document it.....did I mention that Ernie is a engineer.
  Nelson, thanks for sharing and I hope you and Ernie visit on engines.  That is it for me....I am off to Chicago for Thanksgiving and the cold.  Thanks for everones input.

Ron Carbaugh

[firstturn]

Ernie,
  That tee shirt reminds me of a guy standing on the corner selling pencils.  I guess I will have to watch giving away my secrets of search and buy.  Great one Ernie.  The question is do you have any old go kart parts???

Ron Carbaugh

[linglewn]

Ernie,
No, the crashes were in different classes, just happened to be at the same point on the track. I was already in the ER when they rolled Jim in. Keep up the good work and keep experimenting.

Ron,
Have a good and safe trip to Chicago. The last time I spoke to Jim I asked him if he had any of the old kart engines, clutch housings, or other parts laying around because I thought you might be interested. Unfortunately they are all gone. I think he may have given it all away.

Nelson Lingle
73 Jackpiner
71 DKW 125

[Ernie Phillips]

Sachs R & D


Modeling Shop

Transfer L-R: 100stock, 125stock, D stock, D mod, RC4




Intake L-R: D mod, RC$, 125 stock, 100 stock

Ernie P.
Chattanooga, TN

[john durrill]

Ernie,
 I am still looking for the article. We have been collecting files for 8 years on porting and so far i have not found the folder we saved it too.
We have been doing some research for the 125 reed engines porting and it looks like the safest bet for a Six-Day or Berkie is Carls specs. That gets the most mix through the system with out a major sacrifice in reliability .
 We have a paper on 2 stroke air cooled engine  compression ( may be an old SAE paper? ) and one on Sachs 50 cc engine's. The one on the 50's is useful in showing trends with changes. Good for developing rules of thumb.
 If these would help we can send them.
 One thing I do hope we get some input on is changes to the exhaust port shape. Carl left the rectangular lips in place and the Monark GS D spec's remove it. It would have to make a big difference in the timing of waves that pull the spent charge  and some of the unburned mix out into the pipe. Then when the reflected wave from the baffle cone hits it crams the unburned gas back into the cylinder. Almost a super charging effect.
 If Mr Jennings is correct as much as + and - 7 psi pressure in the gas flow.
 Maybe someone can shed some light on what is gained and what is lost with the 2 different exhaust port shapes for the Sachs A/B/D 6 speed engine.
       What a good idea , the latex , to see the ports true shape. Keep it coming please!.
John D.
PS.
 Maybe these 2 pictures will help. They are old but still show how efficient different shapes are to gas flow.

[linglewn]

Ernie,
A "for what it's worth" comment on your transfer port molds. Based on my non-Sachs experience, the three stock configurations look the best. They have the gas aimed high into the combustion chamber and keep the volume of the transfer passage to a minimum. The D mod passage has been enlarged to the point where it would probably hurt rather than help. We never saw a performance improvement with increased transfer flow areas-it just increases the volume of the crankcase which you are trying to keep to a minimum. The RC4 passage has been aimed flat and the length extended. This may work on the Sachs, but my experience says that you get better mixing and loop schavenging with the ports aimed higher. There are so many variables such as port timing and port shape that enter into the equation that it is impossible to make a definitive statement, but I thought I would give you my "for what it's worth" thoughts. Keep testing!

Nelson Lingle
73 Jackpiner
71 DKW 125

[Ernie Phillips]

John, Thanks for your guidance.  A rounded top exhaust port makes life easier on the rings.  We are running 150psi cranking pressure.  I had one engine at 180psi and it had great mid-range pop.  I lowered it after one race because I thought it might compromise reliability.  I've heard the Hodaka boys go as much as 200psi!

Nelson, Interesting observations.  Bigger is not always better as shown in the 100 vs 125 stock duct layout and your own experience.   If Sachs wanted bigger transfers, then the 100 could have easily had them, but didn't.  The D Mod is a real hatchet job and the rubber molds show the kink in the flow path.  Also of interest is that the molds show the mismatch of liner to barrel at the transfer port outlet.  I'm going to do some testing on the RC4 barrel.  I wish I had the time, money and a dyno to benchmark the different configurations.  My seat-of-the-pants meter is not reliable, however, our race results indicate that we make competitive power.  Graham Bell states in one of his 2-stroke tuning books that the trend is to have transfers dump level as opposed to upward.  I'm not sure of what time frame he is referring to.  What works on a high speed, liquid cooled, variable exhaust port, reed engine is not the same as our lower speed, air-cooled, piston port machines.  Too many variables ... "One test is worth 1000 expert opinions."  


Ernie P.
Chattanooga, TN

[john durrill]

Ernie,
 Ill send the paper on compression to you via Yahoo email.
It will give you some insight . Couple that with what Dane  told us
a few months back and you should be on solid ground with any compression changes.
 I have not measure the clearance on a 100 or 125 piston to cylinder  in a long time, but the stock gasket is right at 1 mm after torquing. If you have the room you can use a thinner head gasket to bump compression up in stages.
 You could contact Tony Price on Vinduro. He has a Berkie with a 152 cc alloy barrel that is reed kitted. He located a guy in Texas that does low run custom head gaskets in different thickness. The one made for his engine were copper. I think they ran about $15 a piece .



 From the hop up sheets we have looked at and what Brian showed us on his cylinder coupled with Nelsons  thoughts , rolling the cylinder opening out to match the cases where the transfer ports open would be a good idea. Just reshape the edge so there is no abrupt transfer in shape. The edge would look like S4 or S5 in the picture we posted last. Does that make sense? Very low increase in crankcase volume for the benefit of better gas flow.
 If you are running a 28 mm carb then opening up the round part of the intake port to 28 mm would help  .
 John D.

[john durrill]

Nelson , Ron
 Here are 2 different hop up sheets for the Sachs 100/125.
Could you folks go into the advantages and disadvantages on one over the other please?
One raise the top rear of the transfer ports and opens up the exhaust exit to a full circle. The other spec just widens the ports leaving the stock shape's intact,
 Both jump compression up. Though that's not shown on the Monark sheet.
 MONARK GS SPECS

 CARL'S Bulletin


Thank you.
John D.

[linglewn]

John,
Sorry I haven't replied earlier, but I have been out of town. I'll give you my thoughts, but remember that's all they are. I haven't seen test data on Sachs engines with these mods.

On the first mod, enlarging the eshaust exit should be OK as long as you make sure the eshaust header seals to the cylinder pretty well. a large leak at that point can let in fresh air and cause lean running. Keeping the rounded exhaust shape will help ring life, but won't necessarily help performance. We had very good running engines with the exhaust port "dog-eared" over the intakes. The dimensions indicate that the exhaust has been widened 2mm if the second drawing is correct for the stock width. This should help the performance slightly. The raised transfer in the rear is a big guess on my part. In theory it should help the gasses mix in the chamber and loop to the exhaust. However, we never had success with this arrangement. The best performance was with equal-height transfers aimed slightly high toward the head in the rear. When the back of the transfer is raised, you are essentially reducing the "blowdown" (distance from exhaust opening to transfer opening). Therefore, the dynamics in the crankcase when the transfers open will be affected. Whether for good or bad is a guess. My guess is that it will make for a peakier torque curve.

The second mod raises and widens the exhaust port. My guess is that this will result in more horsepower by raising the RPM at peak torque. As noted the combustion chamber volume must be reduced to maintain compression and torque since raising the exhaust port will reduce the "effective stroke" and cranking pressure. I don't have a comment on cutting the inlet side of the piston skirt. If you have a spare piston you just as well try it.

As has been said before, if you have the hardware and the time, the best solution is make the changes and run the mods on a dyno. The dyno that I currently have is configured for 4-stroke go-kart engines. Otherwise I would be glad to lone it to Ernie (he lives close by) for some tests. Good luck. Let us know if you make either mod.



Nelson Lingle
73 Jackpiner
71 DKW 125

[john durrill]

Thank you Nelson,
 I do understand that with out first hand knowledge all you can offer is advise and your experience on the changes. The possibilities on the top transfer port shapes was a big help.
 Here is a Dyno sheet with the 100 engine after mod's done back in the day. It may help us understand better.



I am still fuzzy on the exhaust port shape change where the pipe and cylinder meet. I will try and get some good pictures of the stock setup made and posted for you too look at. With my limited understanding it would have to make a big difference. The rectangular shape stops where the exhaust manifold bolts up on the cylinder. The pipe slides in to the manifold and buts up against the lips of the rectangle. The gas flow jumps from a rectangular shape to the round exhaust head pipe diameter in about 0 inches. I would think that the reflected wave from the baffle cone would see this as the face of the piston? Sachs had to have done this for a good reason i would think?
John D.

[john durrill]

Ernie,
 Donnie Had some D type cylinder sleeves made up a while back.
 I did not get a good look at one but did see one picture with the intake port shown. It looked like the diagram below.




 Added a bridge and basically turned the intake into 2 D type ports . That should be a better shape for flow. You could go wider with the bridge if you can get away with the bridge being unsupported and the shape of the back of the bridge does not offset the D type advantage. It must have worked for him well or he would not have had several sleeves made up with that design.
 Maybe someone has one they could port map and post a picture of or Donnie could help us out with it? He has had more than a little experience with hot Sachs motors from days gone by i think.
 John D.

[linglewn]

John,
The dyno curve is interesting, but it would really be nice to see the stock engine curve under the identical conditions-exhaust system, compression, ignition timing, etc.

I really don't have any good ideas on the exhaust port outlet. It seems that the mod to match up the cylinder with the pipe should at least not hurt anything. That said, you don't want the reflective wave to cram too much of the exhaust gasses back into the combustion chamber, so perhaps there is a benefit. Remember manufacturing processes have a lot to do with how mass produced items are made. It may have been easier to cast or machine the passage straight through in the shape of the port rather than make it tapered-especially if it made little or no difference in performance.

Nelson Lingle
73 Jackpiner
71 DKW 125

[Ernie Phillips]

My measurements show 28.8mm (100) and 32mm (125) exhaust port width for stock cylinders.  Cranke's 36mm would be for 125 engine.  I think 36 could be problematic for 100 (ring life)  Donnie's sleeve does not have any bridges.  "D Mod" shown has Monark rounded exhaust port.  I recall the old iron barrels having rectangular exhaust header pipes.  I wonder if the rectangular port on the alloy barrel is a carry-over from the old engine design?  As Nelson points out, casting dimensions may be related to production issues – dimensional stability, cooling rates, casing shrinkage, stress risers  ...

Visual aids








Donnies repop "D" sleeve matches my "D" stock exhaust port very nicely

Ernie P.
Chattanooga, TN