ESE's works engine tuner

[wobbly]

Playing with the CCR is a software cheat , but it can have all sorts of bad effects when you are trying to improve on the baseline.
It means the baseline is wrong from day one.
If the sim is optimistic down low , I would be looking at what does change , in reality , during a dyno pull.
The egt , and thus the pipe wall temp will vary considerably.
In nearly all the race engines I have worked on , using 325* below the pipe and 425* at peak power gives great realistic results.
For a "stock " engine the numbers can easily be adjusted to change how the sim reacts at very low rpm by simply changing the wall temp.
The software interpolates beween the two temps , so you can add as many jump points as is needed to reflect reality.

[mantonakakis]

The egt , and thus the pipe wall temp will vary considerably.
In nearly all the race engines I have worked on , using 325* below the pipe and 425* at peak power gives great realistic results.
For a "stock " engine the numbers can easily be adjusted to change how the sim reacts at very low rpm by simply changing the wall temp.

Makes sense, thank you, I'll give that a try!

[mantonakakis]

In nearly all the race engines I have worked on , using 325* below the pipe and 425* at peak power gives great realistic results.
For a "stock " engine the numbers can easily be adjusted to change how the sim reacts at very low rpm by simply changing the wall temp.

Alright, after many tries (including double-checking and slightly updating compression ratio and squish clearance, at least as best as I can with a disassembled crank at the moment...), I'm not able to shift the entire curve down in any significant manner by just changing the wall temps. My final run was just a 2-point curve for wall temp, from 4k to 9k, 370deg to 425deg.
The only other really significant factor I could think of that would shift the overall curve down was altering the combustion efficiency - I decreased it from 82% to 70%, and with the above wall temps, got the following result, much closer.
70% seems pretty low, but what else could make such a big constant offset for my model? Maybe that's fine for an old air-cooled engine?

[husaberg]

The 'easyness " of this type of project depends upon one skill - CAD .
If you are sufficiently up to speed and can model a case on the screen , it is then way easyer to CNC this from billet than it is to make the cores , cast it , then have to machine most of it anyway.
Cylinders are a little different , in that again they are relatively " easy " to solid model , but to then have them 3D laser printed is not a cheap exercise.
This technology is however becoming more mature and cheaper by the day.
The first example of this approach was , I believe , the BSL500,where everything was CAD modelled.
Then the all CNC case was machined from billet , and the cylinders were 3D laser printed , directly off the models that had material added for all the machined surfaces.
A 5 axis CNC machining center could completely finish a case and the cassette cover in 14 Hrs .
And near on 20 years ago the laser printing of 4 cylinders at a time ( the maximum the platten could hold ) cost $5000 usd.

Hi Wob that cover boss on the right looks like it has had welds added on?

the other pic I have appears similar in this detail on the gusset/fillet
https://www.kiwibiker.co.nz/forums/a...5&d=1413102457

I don't think I have seen that pic before do you have any others than are not in this album
https://www.kiwibiker.co.nz/forums/a...p?albumid=4865

[41juergen]

Alright, after many tries (including double-checking and slightly updating compression ratio and squish clearance, at least as best as I can with a disassembled crank at the moment...), I'm not able to shift the entire curve down in any significant manner by just changing the wall temps. My final run was just a 2-point curve for wall temp, from 4k to 9k, 370deg to 425deg.
The only other really significant factor I could think of that would shift the overall curve down was altering the combustion efficiency - I decreased it from 82% to 70%, and with the above wall temps, got the following result, much closer.
70% seems pretty low, but what else could make such a big constant offset for my model? Maybe that's fine for an old air-cooled engine?

I have the same issue like you when moddeling my stock 3XV engine. What I found is that first don't trust any workshop manuals or other sources about the ports timings etc. Make sure that you measure them correctly best as you can. Second the stock Yam pipes (at least from my 3XV) have a "heat isolation" mat inside the belly, that changes the ex gas temp setup in the sim from a "typical" tuned pipe. But even doing all this a best as I can, sometimes I get strange power curves..

[philou]

At second glance, those snowmobiles look quite interesting. So if one were to couple for example a polaris 600 to a conventional gearbox (gears/belt/chain) what would be the best way?

Frits I have post it

[andreas]

Alright, after many tries (including double-checking and slightly updating compression ratio and squish clearance, at least as best as I can with a disassembled crank at the moment...), I'm not able to shift the entire curve down in any significant manner by just changing the wall temps. My final run was just a 2-point curve for wall temp, from 4k to 9k, 370deg to 425deg.
The only other really significant factor I could think of that would shift the overall curve down was altering the combustion efficiency - I decreased it from 82% to 70%, and with the above wall temps, got the following result, much closer.
70% seems pretty low, but what else could make such a big constant offset for my model? Maybe that's fine for an old air-cooled engine?

First of all it's a great bike, superior to it's successor th Lc. Not sure what you mean by a t-shaped pipe, but it's got individual classic pipes with a diverging part that ultimatly ends in an insert muffler- so it will never be "on the pipe"- needless to say it will greatly benfit from a pair of functional pipes. Also, it has bell-shaped combustion chambers, so no real squish.

[Frits Overmars]

Frits I have post it

Thanks Philou, I was just going to start looking for those pictures again. in 2016 I asked BRP-Rotax for the specifics of this engine. It turned out that it was nonexistent; Rotax just wanted to gauge potential interest. So instead of some answers I received an extensive questionnaire.
As far as I know this engine still does not exist. Too bad; I wouldn't have minded a 850cc E-Tec version.

[mantonakakis]

I have the same issue like you when moddeling my stock 3XV engine. What I found is that first don't trust any workshop manuals or other sources about the ports timings etc. Make sure that you measure them correctly best as you can. Second the stock Yam pipes (at least from my 3XV) have a "heat isolation" mat inside the belly, that changes the ex gas temp setup in the sim from a "typical" tuned pipe. But even doing all this a best as I can, sometimes I get strange power curves..

Yes, I found some issues with the manual. The exhaust port seemed to have the dimension flipped (i.e. the manual gave the port height, but actually it should have been shown as height from the deck to top of port, roughly 3mm error). The compression ratio is strangely not listed in the repair manual, but the "combustion chamber volume" is in there, listed as 6.7cc - I measured it as 4cc at zero squish clearance, and at least with my engine disassembled, it appears to be 6.2cc with an estimated 1.5mm squish. I'll have to check both of those again once I receive my new conrods and can put the crank back together...

[mantonakakis]

First of all it's a great bike, superior to it's successor th Lc.

Great to hear the positive opinion, I have yet to feel it run with full stock power, as my crank seals were bad and the cylinders are a bit worn out of spec - I started a teardown to freshen up the bottom end, and managed to bend a rod... oops! But even at its less-than-factory performance level, I've fallen in love! I'm really looking forward to seeing what I can do with it once I get the crank back together, and also with a fresh bore/hone. I thankfully have two, possibly three sets of cylinders I can play with, although one set might not be salvageable and the other is in need of a rebore.

Not sure what you mean by a t-shaped pipe, but it's got individual classic pipes with a diverging part that ultimatly ends in an insert muffler- so it will never be "on the pipe"- needless to say it will greatly benefit from a pair of functional pipes.

By T-shaped, I meant as referenced in the Dat2T help file - there is a small perforated pipe that extends into the diffuser by about 65mm, which matches the header diameter. The help file suggested modeling this as a T-pipe to account for the header intruding into the diffuser:

At least on 6.0.0, I can't add a silencer to a T-pipe on a 2-cylinder (single only), and I wanted to model the common airbox, so I needed to stick with the twin engine model. I figured the most important aspect of modeling accuracy for the pipe would be the restrictor diameter, so I approximated as a very steep rear cone.

Also, it has bell-shaped combustion chambers, so no real squish.

There does seem to be a squish band that's roughly parallel to the outer 50% area of the piston crown. Although definitely not a toroidal combustion chamber (~30mm O.D. bell-shaped chamber, ~4cc), and a radiused transition between the two:

I know not to expect really great power with the Yam12-style transfers (iron liner is the inner transfer wall, not much room to carve into more of a teacup shape), but maybe 30hp would be achievable? It'd be nice to give a stock RD350 a run for its money, since the bike weighs roughly 100kg stock! And the sound at really high revs would be great!

[andreas]

Aha I see, there were different versions of the head. Yes, it will withstand 14k on regular basis.

[wobbly]

Have you run a Turbulent Combustion sim and pasted the results into a new file - if you dont know how , let us know and I will do a quick description.
This makes a big difference , especially to very low and very high power sims as "real " Vibe A and Vibe M inputs take into account even small details like squish velocity.

Husa , those " weld " looking marks are due to that being the prototype case. At the time the CNC guys were just learning how to program the tool paths using NZs first seat of Gibbs - as I had introduced
them to having to reproduce real CNC 5 axis shapes off the SolidWorks platform.They had only ever used 2D CAD drawings previously.

Early on we discovered that the software does not " like " having corner radi in the model that matches the radi of the ball nose being used.
It hunts in the corners , trying to copy exactly the shape with hundreds of extra lines of code..
If I removed the model fillets , the final cut ball nose would simply run into the corner , and leave the fillet naturally - and the code file size was about 20% of the original.

Yes I have a bunch of BSL pics on a disc somewhere.

[mantonakakis]

Have you run a Turbulent Combustion sim and pasted the results into a new file - if you dont know how , let us know and I will do a quick description.
This makes a big difference , especially to very low and very high power sims as "real " Vibe A and Vibe M inputs take into account even small details like squish velocity.

Actually yes, just an hour ago! Quite a big difference in duration compared to my previous prescribed values, smaller differences in the other values. Duration was 31-37deg from 4k to 9k, jumped to 50deg at 10k (just after power peak). Delay increased steadily from 7 to 9deg up to 9k, then jumped to 11deg at 10k. VibeA was a bit higher than the default value of 6, from 7.4-8.6, and VibeM was consistently less than the default of 1.25, at 0.75-0.9. Didn't make a huge difference in the power curve, however. "1" is the default values, "2" uses the turbulent sim, and "3" updates the prescribed values to match the turbulent sim:


After some small adjustments to my approximation of the stock pipe, and some wall temperature tweaks (getting remarkably close to your 325/425 recommendation, still iterating), I've gotten pretty close. The biggest single factor that brought the curve down to reality, though, was decreasing combustion efficiency to 70%. Oh, and I updated to the latest software this morning.


One other factor which might be off is AFR - I'm guessing with a relatively simple carb like the stock 18mm Teikei, AFR is not a flat 12:1 as I have it modeled currently. I assume that the 1981 dyno run I found was running relatively richer at the lower RPM range, maybe rich enough to lose some power? The article did mention poor fuel economy...

[wobbly]

Yep , now you have a good baseline.
I would say that the rear wheel to crank losses are 12.5 to 15% - so this would increase the dyno adjusted to crank result , and thus increase the combustion efficiency needed.

[mantonakakis]

Yep , now you have a good baseline.
I would say that the rear wheel to crank losses are 12.5 to 15% - so this would increase the dyno adjusted to crank result , and thus increase the combustion efficiency needed.

Thanks for all the help! I'll probably be coming back soon to check some of my plans for making more power - especially for any minor port reshaping or timing changes, and maybe for some advice on exhaust port stuffing (way too big at the exit, 28mm diameter vs. 20x25mm port window).

I need to double-check once I get the engine back together, but stock timing is about 183/127 with a 58% of bore exhaust port width, with all 5 transfer ports opening simultaneously. Annoyingly the B-port floors are 2-3mm below the crown at BDC, but they also have a very steep 50deg roof, so maybe there are a few options... E.g. cutting piston crown on the B ports, cutting in a flatter roof, etc. Anyway, I'll come with port mold photos before asking anything specific.