ESE's works engine tuner

[philou]

the only thing that continues to interest people is the hight compression of the crankcase...

[porttiming124]

I just took an old piston to figure out the arrangement of the ports as you suggested. I realize that there is a very big difference.

[wobbly]

Philou , there is no black magic going on with CCR.
Bigger is better , but the limit for reeds is 1.3 as any bigger and the petals become too thin to suit the case Helmholtz and will flutter.
Rotary valve is around 1.24. TeeZee has been bigger , but we have no way of knowing if that was " better ".
Very high performance piston ports ( eg - full house snowmobiles ) all have made more power when made bigger up to 1.3 , but made no more power when going bigger , and the carburation would probably be impossible.
There is a raft of way more interesting things I am keen to learn about - over to you.

[Frits Overmars]

...there is no black magic going on with CCR.
Bigger is better , but the limit for reeds is 1.3 as any bigger and the petals become too thin to suit the case Helmholtz and will flutter.
Rotary valve is around 1.24. TeeZee has been bigger , but we have no way of knowing if that was " better ".
Very high performance piston ports ( eg - full house snowmobiles ) all have made more power when made bigger up to 1.3 , but made no more power when going bigger .

Wob, in the first line of your above quote you mention CCR: Crankcase Compression Ratio. But that collides with everything that follows...

I briefly thought about suggesting CV for Crankcase Volume. But that would steer people in the direction of the already-existing Curriculum Vitae.
Writing clear and simple texts can be a hassle...

[Condyn]

Mixing up Case Volume and Curriculum Vitae surely would not confuse me Frits, hahaha.

[skako]

Frits, I would like to ask.
Can you set the vertical (axial) slopes of the transfer channel depending on the stroke, bore and angle of the transfer duration.
As an example, the transfer duration of 120° and the other extreme of 144°.
These are some possible times for a moped with two transfer channels of the Schnuerle type with a piston-controlled intake.
Are your axial tilts valid for all transfer durations?

[Peter1962]

I have also a question for Frits and Neels : have the optimum axial and radial angles that you kindly published been integrated in Engmod2T software ?

And a more general question : why the heck have all the manufacturers chosen for 66,4 x 72 for their MX engines when research in the GP world clearly showed that oversquare is less good than square, and not a single undersquare engine ever won a GP ?

I know that KTM had a square 250 MX engine, back in the days that they were still a rather small company, but did they change that just to copy the japanese brands who were at that point in time the market and technological leaders in the MX scene ? Or was there a more rational reason ?

In the Enduro world, there seems to be a broad consensus that square engines like the 300's from KTM, or Beta, Sherco and TM are the optimum way to go. BUT they all use 66,4 x 72 for their 250's... Would a factory that would design a new 2T 250 and that has NO plans to make a 300cc version be better off with a square design ?

[Vannik]

I have also a question for Frits and Neels : have the optimum axial and radial angles that you kindly published been integrated in Engmod2T software ?

Yes, it has the option to design a 5-port scavenging systems based on Frits' recommendations, giving the results in either Blair or FOS geometry.

[wobbly]

The undersquare 250MX engines were developed specifically around bottom and mid range torque production , as a higher reving square 250 is not needed at all.
Yamaha had a square 250MX for one year ( 68 X 68.8 )
- its great for 250 Superkarting but useless on an MX track.
And im lost Frits.
CCR is the ratio of the Case Volume/ Case Volume less the Swept Volume ie for a 250cc engine with a 900cc case we get 900/900-250 = 1,38 CCR.
Yes its counter intuitive that a smaller numerical ratio is a bigger case volume , but thats how its always been done and I thought everyone knew that.
An assumption being an error waiting to be revealed ?

[husaberg]

The undersquare 250MX engines were developed specifically around bottom and mid range torque production , as a higher reving square 250 is not needed at all.
Yamaha had a square 250MX for one year ( 68 X 68.8 )
?

With the YZ's as far as i know 83-97 or so were all 68x68mm?
prior to this it was 70mm x 64
after 98 it was whatever its is now 66.?x72.
Honda as far as i know went to the long stroke in the Works RC's in about 79.
Villers and greeves had the LS dimensions sorted back to the 50's
Std Villiers never worried about pesky rollers being oversped, as they has plain bearings (bronze bushes) on big and small ends just like a modern MX foul stroke.

How long did they last on a STD bottom end Grump? was it the load that killed them or the the milage?

[Grumph]

Re Villiers. It was only the very early engines which had plain big ends. But plain bronze bush small ends lasted nearly till the end. And surprisingly they did last quite well. What usually broke was the gearbox shell once you got any HP out of them. Or the rod. I remember seeing a DOT with the rod wrapped around a frame member - but still with a sound big end.

Still watching with interest Rob - and reading Wob's contributions too. Still learning.

[Frits Overmars]

im lost Frits. CCR is the ratio of the Case Volume/ Case Volume less the Swept Volume ie for a 250cc engine with a 900cc case we get 900/900-250 = 1,38 CCR.
Yes its counter intuitive that a smaller numerical ratio is a bigger case volume , but thats how its always been done....

That's how I do it too. A bigger crankcase volume for a given cylinder capacity yields a smaller Crankcase Compression Ratio; nothing wrong with that.
But I feared that your post might confuse some folks. I do not want to ramble on but let's look at it one more time, for clarity.

Philou , there is no black magic going on with CCR.
Bigger is better , but the limit for reeds is 1.3 as any bigger and the petals become too thin to suit the case Helmholtz and will flutter.
Rotary valve is around 1.24. TeeZee has been bigger , but we have no way of knowing if that was " better ".
Very high performance piston ports ( eg - full house snowmobiles ) all have made more power when made bigger up to 1.3....

You mention CCR and then you write "Bigger is better...etc" without ever using the word Volume, so a layman would read it as "Bigger CCR is better".
And I'm sure that is not what you wanted to communicate.

why the heck have all the manufacturers chosen for 66,4 x 72 for their MX engines when research in the GP world clearly showed that oversquare is less good than square, and not a single undersquare engine ever won a GP ?

In the Enduro world, there seems to be a broad consensus that square engines like the 300's from KTM, or Beta, Sherco and TM are the optimum way to go. BUT they all use 66,4 x 72 for their 250's... Would a factory that would design a new 2T 250 and that has NO plans to make a 300cc version be better off with a square design ?

Long-stroke two-strokes have better blowdown and transfer angle.areas than square or short-stroke engines. With the same exhaust and transfer port timings they will rev easier.
Or, to look at it from the other side: they can make their power without the need for need high timings that would spoil rideability.

Undersquare means: the bore is smaller than the stroke. So an engine with 54 mm bore and 54,5 mm stroke is (granted: just) undersquare, or long-stroke as I prefer to call it.
And long-stroke Honda, Yamaha, Suzuki and Aprilia engines did win a GP or two....

You write that square engines like the 300's from KTM, or Beta, Sherco and TM are the optimum way to go.
Sure, if you already have a twofifty on the shelve and all you have to do is overbore the cylinder. From a technical point of view it's not the best solution, but try telling that to the bean counters. A factory that would design a new two-stroke 300 and that has NO plans to make a 250cc version, would definitely come up with a long-stroke 300.

Frits, Can you set the vertical (axial) slopes of the transfer channel depending on the stroke, bore and angle of the transfer duration.
As an example, the transfer duration of 120° and the other extreme of 144°. These are some possible times for a moped with two transfer channels of the Schnuerle type with a piston-controlled intake. Are your axial tilts valid for all transfer durations?

I did, Skako. You can find the axial angle calculations below, and as you'll see, transfer durations do not play a role. But a transfer timing of 144°?
For an engine with only two transfer ports I think it would be best to use the radial angles of the A-ports below and the average of the axial angles of the A-ports and the B-ports.

[philou]

skako, have you tried the wave simulator that I sent you?

a comparison with the one you developed?

[skako]

skako, have you tried the wave simulator that I sent you?

a comparison with the one you developed?

I couldn't get it to run. Sorry I didn't get back to you. It accepts the input data, but I don't get the output. I've stopped, I'm learning and looking at how to rearrange and expand my programming code. If I manage something, I will contact you.

[philou]

it only works in MS-DOS. works under win xp.

programmed in the years 1996