Anybody doing any computer analysis on our old piston port, air cooled engines? Over the last year I've acquired a few 100-125 Sachs cylinders with very different porting execution (huge exhaust, hogged out transfers, boost ports, worm ports, mirror finish polishing on one and then ruff as a cob on others). Without having to install and tune each configuration, I thought that inputting data into a computer simulation program and seeing how each change affected engine performance would give a way of determining which cylinder (or specific mod) has a chance of actually improving performance. For example, do you get better results by improving port geometry (time-area, entry-exit, direction) or can you just leave the ports alone and build a better pipe to evacuate and recharge the cylinder? Is it reasonable to expect that significant performance gains across the desired RPM range could be achieved with the proper port/pipe combinations beyond what is generally known (Cobb, Cranke, Monark GS, Popular Cycling, FMF, TX specials, Circle-F)? I've looked at programs by TSR, MOTA, Bimotion. (Disclaimer: I know for a fact that the stock Sachs engines perform very well, have good reliability, and have won many races. I'm just curious)
Ernie P.
Chattanooga, TN
Not being specific to motorcycles, but having experience as a backyard mechanic port matching and smoothing ports in big block chevy engines, it is well known that highly polished ports do not work as well as smoothed non polished ports on the intake side, but polished ports work best on the exhaust side. The reason is because on polished ports the fuel in the air/fuel mixture tends to stick to the port walls and cause turbulence and draw the fuel along the port walls, but after combustion burning of the fuel, the polished surface flows best. I have read this in many publications from experts in the porting field regarding big block and small block chevy performance modifications. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
Sounds like the Phillips Vintage Cycles skunk works has a winter project. :D
Brian
'73 Berkshire
Ernie,
I have seen many attempts at trying to resolve this age old delima. In my book there are two separe issues to address.
1. Build a flow bench for a two stroke cylinder and try and flow it with and without the chamber.
2, Build a load dyno to bolt up the engine, carb and pipe to do load testing with simple digial/memory graph hardware so that you don't have to blow an engine test.
Study the graphs and put your best combination in the bike and then test using gearing to set the bike up for the best performance based on the type of racing you are doing.
If I remember correctly we have an ole National Caliber Kart Racer(Nelson Lingle) that may have a engine dyno and a lot of knowledge.
Just my thoughts.
Ron Carbaugh
Ernie,
I used the Bimotion software several years back. They had a demo
program you could down load and run.I tried it out with the ports on my sons 75 175 KTM and his pipe measurements just to see how close it was. It was in the ball park BUT the pipe that came stock was different than what we got for measurements from the software.
I think there are too many variables for any software model to give us accurate data.
I asked a friend who is a good tuner and builds good pipes for road racing about the software and he was of the opinion that is just was not possible to use it except as a starting point . Then you would need to do a lot of testing and cut an try to find what would work best on your particular engine.
Gordon Jennings Book will get you just as close and give you more insight on the interaction of the cylinder ports and pipe design i think.
Ron gives good advise if you want to get the best out of a design.
I bounce all kinds of Hair Brain ideas off him on a regular basis [:p]
We are going through this right now with an Iron Barrel 125 engine. Trying to just get the best out of the design with out sacrificing reliability or moving the power up into a narrow band.
I have asked for advice from several good engine builders but have found out unless you have already worked with that design ( specific cylinder in this case) enough to " know " it you can not offer reliable advise on specific changes. Just some things to watch out for [B)]
I can send you a short cut to the Jennings book on line and have 2 other articles , one by EC Bert and I think the other by Harry Taylor that can help you.
Port width and shape is a biggie. The ports shape , type of ring's you have to work with and pistons design , limits what you can do safely. Get that all maxed out for an engine and.............
You get into raising and in the case of the intake lowering port openings . The transfers work together with the exhaust. I am told there is a narrow window ( Mathematical relationship) for change between the exhaust height and the transfer height. Get outside that window and you go backwards. You can go back and change the pipe and or the duration of the exhaust or transfer and jump forward sometimes. Sometimes you have to start all over with a new liner or cylinder.
Ron if i am a off center with any of this please jump in.
Ernie i will gladly pass along anything i learn from my project. The goal we are shooting for is get the most out of that engine with out moving the power band up more than 500 RPM or making the engine unreliable ( a 2 day trials type engine ). Just make it work the best it can with the iron cylinder. Its a bit different than building one for CC or MX.
I know others on here know a lot more than i do about this type of thing. All i could do is pass along what i" think " is accurate [:I]
John D.
I am by no means an engine wizard but what I know about them and what I know about computer simulations I tend to agree with John. There are no doubt simulations produced in house at companies like KTM, Honda, etc that can be extremely accurate, but those are surely built for a specific engine. I think anything available to the public at a price that an individual can purchase will not have the fidelity to be of much use beyond getting you to a starting point. I would think for a simulation to be accurate enough to do meaningful testing all on computer it would have to be written for a specific engine and not a generic program.
I know this is not the answer Ernie wants, but I think the most practical way to test would be with two bikes on the track at the same time, one your test mule and one your baseline bike. It will be time consuming, but you get direct results in the environment the machine will have to perform in, so it is by nature definitive.
Brian
'73 Berkshire
Let's get a base line on this discussion....there are probably no wrong answers and some ways of developement meets the needs of certain indiviuals. Like Brian says about two bikes is OK if you have money and a lot of time...mostly a lot of time. What John is saying has worked for a lot of people who have the background and do take the time to read articles and books written by notable people.
The items I discussed do not break the bank and can be used to test while at home/shop and then test at the track. I think one thing that Ernie was saying was Make It Easy on Me where I don't have to put wing nuts on the engine bolts to change and test and change and test.
I am happy to see this discussion and I should add that Ernie and his crew went from blown engines and busted shift keys to really winning a lot of GOLD this year. Ernie has several things on his side. He doesn't give up and he knows how to test and double check his work. The other thing is Ernie grew up in a area that was tough racing and to be a Pro you were a excellent rider....I know I raced in that area it it had some great rider in LA(Lower Alabama).
Ron Carbaugh
Ron,
Thanks for the compliment. I wish I had all the answers, but I don't.
Ernie,
We modified hundreds of racing engines back in the 6o's and dynoed each modification to determine the results of all changes, and then raced the ones that ran the best and trashed the rest. Important factors were port timing, port shape, crankcase volume, port transfer passage shape and volume, direction of flow of the transfer ports into the combustion chamber, combustion pressure, and of course ignition timing. We were looking for maximum horsepower, so usually ended up with high ported engines with little low-end torque.
We also did a lot of dyno testing with special instrumentation installed on test engines. We measured fuel flow, air flow into the carbs, crankcase pressure, combustion pressure vs crank angle, and (the most interesting) the gas flow direction in the transfer passages vs crank angle. The tests showed that a good running engine had enough combustion pressure at the time when the transfer ports opened to force combustion gas into the transfers and pressurize the crankcase. The colume of gas in the transfer passages then acted like a spring to force the cooler crankcase gasses into the combustion chamber. The direction of flow into the combustion chamber seemed to be important in making an engine run smooth at full power. If an engine runs rough, it doesn't matter how much power it makes because it won't last long. All of this was done on reed valve engines with a fairly short stroke. Add piston port, rotary valve, long stroke variables and you may get different results. Of course the expansion chamber has to be designed to match the rpm range of the proting.
As far as a computer simulation for all the variables of a 2-stroke engine, I have not heard of one. I know that wonderful things can be done by computer simulation, but I'm not sure there has been enough interest in the older engines to justify the expense and effort to produce one that could give reliable information.
Nelson Lingle
73 Jackpiner
71 DKW 125
Gentlemen, Thank you all for your well thought out comments. Hopefully others will chime with their tuning experiences.
Mike, Sounds like I don't need mirror finish. Thanks.
Ron, "Wing nuts on the engine bolts" – now there is an idea that fits right in with my LA up bringin':D.
Nelson, I didn't know you were such a serious racer and engine builder. We need to get together some time. I'd like to hear more.
John, I'd like to see Harry Taylor tuning info. Thanks for your continuing interest in always wanting to make it "just a little bit better.".
Brian, It's all your fault. Until I rode the SoCal Berkie, I was satisfied. Now I'm not.
Ernie P.
Chattanooga, TN
Too many choices!
(http://i250.photobucket.com/albums/gg276/ernie7711/sachsportingcyl125.jpg)
Ernie P.
Chattanooga, TN
I posted these pictures of my SoCal Berkie ported cylinder a while back but since this topic came up I will putn them in here too so we can compare.
(http://www.the-gunfighters.org/Porting1.JPG)
(http://www.the-gunfighters.org/Porting2.JPG)
(http://www.the-gunfighters.org/Porting3.JPG)
Only the bottom 2/3 of the transfers look like they were ground, the top 1/3 and the transfer windows look stock. There is minor polishing of the exhaust port towards the exit but the port height looks stock because there is some casting texture left right at the liner intersection although I admit I did not measure them. I have a 125 cylinder that was on the bike when I got it that is ported exactly like this 100 cylinder.
Brian
'73 Berkshire
It looks like the transfers at the base gasket area have been ground much "wider" on my cylinder than any of the ones Ernie posted.
Brian
'73 Berkshire
Ernie,
Nelson has a lot of history with two strokes. He and his buddy, when he lived in Texas, were known as the guys that came up with BIG NEW IDEAS for karting engines and clutches. Some rumors of NASA connections....and the rumors were true as I was fortunate enough to have some early teflon coated engine parts done a NASA. Nelson may want to elaborate as some people think of karting as a kids game, but this was serious business and there were a lot more injuries than people were aware of from those early days.
Ron Carbaugh
Ron, you really have a great memory and help to bring back some fond memories of my own. My buddy, Jim Akkerman, and I worked together as NASA engineers. As such, we really enjoyed experimenting and developing new ideas. Jim was the mastermind behind most of the development work and the owner of Akkerman Engineering. We developed and produced the full circle crank for McCulloch and West Bend kart engines. We were also the first to develop a functional "slippy" clutch for use with the Margay gearbox. We raced most of the enduro classes sanctioned by the International Kart Federation (IDF), and were fortunate enough to take home more than our share of awards-including several National Championships.
The accidents you mentioned are not-so-fond memories. In 1970 at Dallas International Raceway, Jim and I both won our first one-hour race and then got directly into a kart in a different class for another one-hour event. We both crashed on the same turn about halfway through the race. The results were a broken back for me and a broken leg for Jim. It was a long ride back to Houston.
That's probably more than anyone really wants to know, but thanks for jogging my memory.
Nelson Lingle
73 Jackpiner
71 DKW 125
Nelson, Fascinating story! Thanks. I hope is wasn't two best friends and racing buddies that knocked each other out. If so, it really was a l o n g drive back to Houston ;). -EP
Seen at Zink 2008 RR but think it originated in TEXAS.
(http://i250.photobucket.com/albums/gg276/ernie7711/PA310027.jpg)
Ernie P.
Chattanooga, TN
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
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
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
Sachs R & D
(http://i250.photobucket.com/albums/gg276/ernie7711/PC030253-1.jpg)
Modeling Shop
(http://i250.photobucket.com/albums/gg276/ernie7711/PC030210.jpg)
Transfer L-R: 100stock, 125stock, D stock, D mod, RC4
(http://i250.photobucket.com/albums/gg276/ernie7711/PC030217.jpg)
(http://i250.photobucket.com/albums/gg276/ernie7711/PC030239.jpg)
Intake L-R: D mod, RC$, 125 stock, 100 stock
Ernie P.
Chattanooga, TN
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.
(http://farm4.static.flickr.com/3169/2683794910_17cd273b13_o.jpg)
(http://farm4.static.flickr.com/3244/2682977551_ea92837c36_o.jpg)
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
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
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 .
(http://farm4.static.flickr.com/3137/3082131849_4005070c6c_o.jpg)
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.
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
(http://farm4.static.flickr.com/3243/3084951659_458d539b32_o.jpg)
CARL'S Bulletin
(http://farm3.static.flickr.com/2398/2167003433_e6e6c27bfa_b.jpg)
Thank you.
John D.
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
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.
(http://farm3.static.flickr.com/2390/2167796530_9d11895dfa.jpg)
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.
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.
(http://farm4.static.flickr.com/3061/3090384509_5fb0efbe51.jpg)
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.
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
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
(http://i250.photobucket.com/albums/gg276/ernie7711/PC080265.jpg)
(http://i250.photobucket.com/albums/gg276/ernie7711/PC080266.jpg)
(http://i250.photobucket.com/albums/gg276/ernie7711/PC080267.jpg)
(http://i250.photobucket.com/albums/gg276/ernie7711/PC080268.jpg)
Donnies repop "D" sleeve matches my "D" stock exhaust port very nicely
Ernie P.
Chattanooga, TN
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)
"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
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.
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
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
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.
Quotequote: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)
(http://farm4.static.flickr.com/3243/3084951659_458d539b32_o.jpg)
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 :D
Bob W
(http://i52.photobucket.com/albums/g8/BobWardlow/DSCF1191.jpg)
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.
(http://farm4.static.flickr.com/3157/3099750212_62bd2be9d9.jpg)
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.
(http://farm4.static.flickr.com/3131/3099750142_87cd38b254.jpg)
I would have added 2 more 1/2 inch holes on this kit for cooling
(http://farm4.static.flickr.com/3062/3098916391_a9e7150330.jpg)
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.
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.
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
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.
John, I forgot about 100 being Sportsman and "reed" legal. Something to think about ... Thanks -EP