ESE's works engine tuner

[husaberg]

Also a short introduction and a few comments.. My name is Vagelis, from Greece

Yet, in a couple of Honda port maps I've seen, fronts open earlier than the rears.. Does the latter serve any particular cause? (eg a different power/torque delivery)
Or is it just a pattern in older Honda cylinders?


And about the books you discused in earlier posts: Has anyone read "The high performance two stroke engine", by John Dixon?

Here's the front cover of the book:
Attachment 250770

Hello Vagelis

I can't speak for if its right or wrong, but both Bell and I think Robinson as well do offer an explanation on the staggered transfer timings in both directions.
I had not seen the book before, are you able to show some exerts of its content.

PS I loved the movie, great sound track. .sorry
.

On a different subject has anyone ever seen a map of the KTM50 ignition curve, because they would have to be the most petite set up ever.



They are also relatively inexpensive if not totally reliable.
They also have what would be the smallest easy to add water pump to an Air cooled crank or oil pump set up to convert to liquid cooled.

[TZ350]

Page 360 interesting posts to be collected here.......

... simple calculations: they are only meant to help beginning tuners on their way and a lot of more or less important facors, like compression ratio, ignition timing, type of fuel, carburetter diameter, crankcase volume and angle*areas, are not taken into account.

Attachment 250970

the important thing is that lower exhaust timings need bigger header diameters ... the speed of sound. Starting with 550 m/s will get you in the right ballpark, after which you can vary this value according to your findings.

Final remark: the calculation of the tailpipe restrictor diameter is critical: you can only apply it to engines that are thermally sound. Air-cooled engines are not...

[TZ350]

My simulation is getting closer to the real thing, most of the difference was adding realistic rpm related pipe temperatures and running the simulator using the turbulent option.

[Frits Overmars]

Attachment 250785
An interesting look at a Kreidler transfer passage.

The Kreidler engine shown by TZ350 was cutting edge technology in 1962, but I do not think any of you want to copy transfer passages that, together with twin rotary disks and a twelve-speed gearbox, produced all of 10 HP out of 50 cc.
In case you wonder: the transfer timing was 142°; the single exhaust was way over 200°. Don't try this at home....
Below are some more pictures of the same engine, showing the twin carbs and the screwed-in caps that gave access to the transfer ports for easy modification.
You can also see the hand-operated three-speed gearbox behind the foot-shifted four-speed box.

[Grumph]

First off, Frits, thank you very much for sharing your knowledge and experience with us.

Following the Kreidler pics, when i was looking at your 50cc cylinder, i did wonder about inlets...and thought maybe the kreidler dual disc setup may be in your mind....

I'm an old guy whose days of working with state of the art cylinders are way behind him, but I was looking at pics of a 70's Rotax 125 cylinder recently and it's very apparent how it has evolved into the Aprilia. The amount of wall between ports has shrunk noticebly over the years which leads to one question...where on the Aprilia cylinder is the ring peg/gap ? In that maze of ports i can't see room.

The Honda cylinder previously mentioned with the obstruction to flow apparent brought to mind one I did on a customers instructions...he wanted it removed so I did. End result - gained 2 hp in the midrange - lost 2 hp off the peak...

Greg

[Frits Overmars]

First off, Frits, thank you very much for sharing your knowledge and experience with us.
Following the Kreidler pics, when i was looking at your 50cc cylinder, i did wonder about inlets...and thought maybe the kreidler dual disc setup may be in your mind....

Yeah, as a nightmare. Just think of any error you can come up with: Kreidler had it. Both disks were axially fixed on the crankshaft; they could not nestle against their covers and it took hours to press (!) them into a position that would not yield too much leakage or too much friction.
And take a look at the inlet tracts between carbs and disks. Nice tight U-turn, wouldn't you say? No, for my cylinder I thought up something completely different:
the 24/7-system. I've got no time to elaborate now, but you may find some more info here: http://www.pit-lane.biz/t117p376-gp1...es-aprilia-rsa .

I'm an old guy whose days of working with state of the art cylinders are way behind him, but I was looking at pics of a 70's Rotax 125 cylinder recently and it's very apparent how it has evolved into the Aprilia. The amount of wall between ports has shrunk noticebly over the years which leads to one question...where on the Aprilia cylinder is the ring peg/gap ? In that maze of ports i can't see room.

The devil is old, Greg. Below left is a drawing I did when working on a Rotax cylinder in 1980, and next to it the 1980 cylinder itself and a recent Aprilia cylinder.
You are quite right: not that much difference in over 30 years.

The ring peg is right opposite the exhaust: the only decent place for it. Each time the ring passes over the exhaust port, it bulges out a little and then gets shoved back in its groove when it runs over the top and bottom port edges. If the ring peg is not diametrically opposite the exhaust port, this shoving back will cause the ring to rotate in its groove and every time it will hit the peg from the same side until the peg works loose....
Don't worry about the ring gap running over the C-port. The Aprilia's C-port is now 15 mm wide, but it has been as wide as 22 mm and even then there were never any ring problems.
Generally speaking you can say that the ring gap is safe over a C-port width of up to 40% of the bore. For steel rings that is; I never tried it with cast iron.......

[F5 Dave]

Frits, thank you for your time & knowledge. We have been talking a lot about the RSA & cylinder transfer ducts and learning a lot. Looking under the sheets a little further one wonders what the crank would look like? If super lightweight stuffers would be employed to reduce the crank area so more volume could exist outside of the turbulent area yet retain a suitable case compression ratio?

I have read about charge in the duct area being most important, - this would tend to indicate that the reed entry was not so critical, but I heavily suspect having seen (and produced) some less than successful full reed conversions that the reedblock angled into the crank area is not desirable. Thus the thoughts above. Pity there is that damn awfully inconvenient rod thrashing about the interface else you could separate the two areas.

[dinamik2t]

_

Thank you for the explanations (plain) Frits
In some cylinders the A ports have a reducing width from top to bottom, without any aux or bridged exhaust ports being over them. Is that the same reason for this shape? Avoid short-circuiting when A-port open - one that cannot allow mixture to return to the cylinder?

_

Thank for all the info either. It seems every configuration has its purpose at some point and each engineer has his own approach.
By the way, I uploaded some new files, plus the .pjt file so that everyone can open it right away.
http://users.uoa.gr/~sph0800108/mode...17-11-2011.rar

_

I think it might not be legal to scan/upload content from the book. Plus, I am not sure if it's allowed do thus on this board. On the other hand it would be a promotion gesture
Here's the index page from another site. If I'am allowed, I can find a couple of pages from a specific subject that might interest you! As a demonstration of the content..

[Grumph]

Thanks for the link Frits - i see now what you're trying to achieve.

Reminds me of an incident a few years back when a friend of mine was running an "E" model TZ 250 Vtwin. One meeting it went exceptionally well - when he checked it proved to have a broken reed petal. He asked my opinion so I advanced the suggestion that he start cropping reeds back until he found the optimum amount of reed required for satisfactory starting and midrange....
He never followed up on the idea but I offer it here for what it's worth....

[wobbly]

Re power graph for Dynamik2T.
This is where you need experience to dictate if the sim result is realistic or not.
Having a 82.5* Ex with a pipe 895 long will NEVER have peak power at 12500.
I ran a baseline with all your inputs, except changed the comb to prescribed ( turbulent is very slow).
Then changed pipe wall temp to 50* as I usually do.
This gives max power around 11500 as I would expect.
There are a heap of other issues to look at, including the warning about the transfers being too close to floor of the Aux ports.
Drop the transfers as they are too big now, this will increase blowdown,and that is what it needs more of.
Bottom line here is, what rpm peak power do you want, and what max rpm do you want to limit to.

[Myron]

Frits, wondering if you would be willing to comment further on the RSA125. My question at present is in the downsweep of the exhaust duct. I believe you are at roughly a 30 deg downsweep from center of exh port to center of the exh duct outlet. Was there any testing on varying this angle flatter or steeper? How important do you view this angle? I have a significant library of cyl specs from all different forms of two stroke applications, and it seems to run the gammit. I have some hunches but cant really prove or disprove any of them with my available resources. Does this angle affect the looping direction of the transfers? It would seem to me a flatter angle would obviously give a better time area, but would also tend to "bend" the charge from the transfers in a short circuiting manner quicker. Or maybe you view the roof of the exh port as more important? Any experiences or thoughts?
Myron

[dinamik2t]

Thanks for checking the file
This exhaust is actually an RS125 exhaust, with about 55mm of length added and a few minor diameter changes to keep the angles the same. It was a custom made pipe by a friend with a TIG a long time ago, as an improvement over a crappy pipe from some local dealer. The reason why we added that length back then was to bring the power down to that RPM point from the 12.5k.
I started simulating at about 11.8 and by altering specs, advance and afr it went that high, which was curious but pleasant. I didn't know it wasn't right!

To confirm from my side also, here's the result when changing pipe wall temp to 50C. It's Turbulent model result (bless 4-core cpus, less than 10min for a run )
I then lowered by 1.5deg the TFRs and played with advance and afr. In short, top power went up a little and overrev improved much. I 'll keep experimenting.
I think I am fine with the lower rpm top power. Could it go up to 12.5 or even 13 with decent overrev (say, over 21-22kW)? That's about my rpm limit.
Gearing isn't close-ratio and rpm drop a lot in first gears. It could benefit from the extra power in overrev, right?



If I used a thermal wrapping on the pipe would the results went closer to the previous curve? Or is it a matter of length? I woudn't like to ask for a complete explanation (given your free time), but could you guide me on where to look for the answer here? Or give a hint perhaps..

One last thing. I have noticed that modern MX-125class crankshafts are very wide (>54mm), while kart cranks are wery thin (~48mm). Both for the same stroke of course. Say we used a 5 or 6 speed shifter kart with a typical clutch for the comparison, so that are both "models" equal on the transmission part.
Could you explain the physics here?
I say there would be bigger momentum for the heavier crank and bigger inertia also. So, it would be harder to rev on the one hand, but also harder to 'unrev' (good thing)?




ps. I know it's wrong, but it's actually dinamik. that's the name of the bike! I have been using it a long time as a username, so I kept it here also so as not to forget it.

[TZ350]

The yellow trace is the pressure at the exhaust port.

Wob am I reading this right?



On the left the pipe is sucking the cylinder down to late for the transfer port opening TPO.

And on the right the exhaust pulse is arriving back to early, before the transfer port has properly closed TPC.

[TZ350]

And the combustion variables are as calculated by the program using the turbulent model - you use burnrate prescribed until the model is well refined,then run turbulent ( very slow) and transfer the results from that run manually,to speed up later sims by using real burnrate numbers.

Hi Wob, after running the sim in turbulent mode where do I find the real burn rate numbers?

[dinamik2t]

TZ, you will have to get them from Post2T. Instead of selecting 'power' graph, you should select 'Delay', 'Durat' (duration), 'VibeA' and 'VibeB'. Then manually transfer the values to the respective columns in the Combustion file. It takes some time...

Wobbly, could you tell us after which alterations the Turbulent numbers change? For example, if I make a minor EXpipe dimension change or a port TA change, do I have to run turbulent again to get new-correct delay/duration/vibe numbers? From what I remember from the manual, it's only affected by the main combustion variable themselves (adv,afr), but I am not sure.