ESE's works engine tuner

[Peljhan]

I remember this story from Jan, nice insight.

Wouldn't be a transmision disturbed more when upshifting with quickshifter as shift is allmost instantanious and when downshifting, clutch is usually used?
I wonder, maybe not, as crank need to drop revs only few hundreds when upshifting.

Maybe he should go play games, where only one ball is required instead of kicking poor Aprilia

[Frits Overmars]

Wouldn't be a transmision disturbed more when upshifting with quickshifter as shift is allmost instantanious and when downshifting, clutch is usually used? I wonder, maybe not, as crank need to drop revs only few hundreds when upshifting.

Upshifting is usually done one gear at a time. Downshifting may be less friendly to the transmission, with some riders stomping on the pedal three times at once.
And clutches are for starting only, these days.

[lodgernz]

This would have been interesting. Alfa Romeo 2T V8 F1 engine prototype.
Looks like the intake is under the crankcase, so presumably used reeds.

[jamathi]

Who knows?

As long as we are accelerating in one gear, a high crank inertia is indeed a blessing for the transmission and the rear tire because it will smoothen the torque spikes, caused by the combustion pressure.
The downside is that when shifting gears, the energy required to change the crankshaft rpm jerks the transmission and the tire. Especially downshifting, when the cankshaft is suddenly forced to rev much higher, can cause a heavy burden, corresponding to a multiple of the power produced by the engine.

By the way, some of you may remember the first outings of the Aprilia RSA125, which was sidelined by a broken inlet disk shaft a couple of times. The shaft calculation was based on the friction between the disk and the inlet cover, caused by the crankcase pressure, but the disk's inertia was neglected.
Jan Thiel warned that an 8 mm Ø shaft would not be strong enough, and he was proven right by one rider in particular with a 'heavy shifting down' foot.
There are some great pictures of the way the rider reacted. They are copyright-protected so I cannot show them. But in case you're curious...
https://www.google.com/search?newwin...w=1175&bih=594

The inlet disc shaft was never calculated. I remember that I was hesitating between 10 and 12mm, then Gigi came by and decided on 8mm..... I was angry and went away! Later the problem was solved by putting a shock absorber in it.

[Tim Ey]

This would have been interesting. Alfa Romeo 2T V8 F1 engine prototype.
Looks like the intake is under the crankcase, so presumably used reeds.

Isnt that the Mercury or Evinrude V8 of the Rudezon?
https://www.youtube.com/watch?v=RoiWpJLokEc

[wobbly]

Jan , were you too kind to tell Gigi he didnt know shit , and it should have been him who went away angry.
You were lucky the great leader didnt come by and tell you to use a chain drive - or something even dumber.

Seems like exactly the same torsional shock load that the first Cosworth DFV had with its cam drive . Duckworth fixed that with a super clever system of multiple tiny torsion bars with levers
inside one drive gear.

[lodgernz]

Isnt that the Mercury or Evinrude V8 of the Rudezon?
https://www.youtube.com/watch?v=RoiWpJLokEc

Certainly looks like it. I guess I was misinformed. Still awesome though.

[husaberg]

Jan , were you too kind to tell Gigi he didnt know shit , and it should have been him who went away angry.
You were lucky the great leader didnt come by and tell you to use a chain drive - or something even dumber.

Seems like exactly the same torsional shock load that the first Cosworth DFV had with its cam drive . Duckworth fixed that with a super clever system of multiple tiny torsion bars with levers
inside one drive gear.

He used a quill drive torsion bar on the Cosworth twin as well.
but that was an Norton mandated 360 twin no center bearing an a heap of other silly stuff. Like high mounted water pump etc

[Muhr]

Hey all!
Has anyone tried pushing the limits in terms of cylinder offset?
And if so, what kind of difference in character did you see.

[wobbly]

The issue with offset is that it makes the Exhaust especially , timing asymmetric.
Thus you may get a gain from it opening early , but then it closes later - that is where "going to some large limit " is heading.
Test like this at Vortex , just indicated that the opening timing was wrong in the first instance.

[Frits Overmars]

The issue with offset is that it makes the Exhaust especially , timing asymmetric.
Thus you may get a gain from it opening early , but then it closes later

Opening earlier and closing later did not sound asymmetric to me so I tried to do the math.
I chose values that are hopefully useful in practice: 54,5 mm stroke and 110 mm con rod length, first without offset and then with an offset of no less than 10% of the stroke: 5,45 mm. The engine may not like it, but my point is to make the effect of the offset crystal clear, and exaggeration can be enlightening

Whether the offset causes the exhaust to open earlier or later, depends on the direction of crankshaft rotation. I chose 'with' but you can mirror the values if you prefer.

Hopefully we are all familiar with the fact that any offset increases the distance between TDC and BDC (you may not believe me, in which case I have some more shocking news for you: the earth is not flat and not all politicians are honest).
More shocking news: the crank angle from TDC to BDC is larger than the crank angle from BDC to TDC (no, this does not mean that the piston will get lower and lower and drop out of the engine after some time). The net result is that neither TDC nor BDC are where you'd expect them to be in a zero-offset situation.

The only logical approach I could think of, is to use one and the same cylinder for the offset/no offset-comparison, and set the piston flush with TDC on both occasions.
I chose an exhaust timing of 196° which corresponds to a port top edge 26,82 mm below TDC, and a transfer timing of 130°, corresponding to 41,57 mm below TDC.

An offset version of the crank angle/piston position table ought to show all 360 crank positions because of the asymmetry (from TDC to BDC is not the same as from BDC to TDC) but I only show the part that is relevant to our port timing comparisons.

If you search for the crank angles corresponding to the 26,82 mm and 41,57 mm port positions, you'll notice that they deviate somewhat from the values in the zero-offset table, but not much.
If I didn't mess up the math, the exhaust opens 0,5° later and closes 1° later. Yes, it's asymmetric, but I wouldn't lose any sleep over it.

[Muhr]

I did something similar to see when something interesting happened..

Some examples of 4 strokes with offset

Suzuki does not offset its cranks. Honda has a 4.5mm offset. KTM and Husqvarna use 5mm of offset. Kawasaki has 8.5mm of offset, and the Yamaha YZ450F offset is 12mm(60,8 Stroke).

[OopsClunkThud]

did a quick mockup to see how the offset impacts the timing as it seemed like it could give more degrees for blowdown.

Ex: 190°
TR: 130°
offset 14.78mm (to give 185° on the down stroke, 175° on the up)

With zero offset there are 30° of blowdown
With 14.78mm offset there are 31.3° of blowdown

1.3° of extra blowdown with the same overall exhaust timing may not be much, but combined with the reduced side loads on the piston it seems like it could be useful configuration.

[Frits Overmars]

14,78 mm offset in an engine with 51 mm stroke and a 97 mm conrod is a lot. You'll either need a real bigbore piston (not recommendable for a two-stroke) or you'll need to offset the cylinder. And yes, the difference in side load on the piston can be worth while.

[ken seeber]

D I R E C T C Y L I N D E R I N D U C T I O N (DCI)

So, after running the system (some time ago) with the DCI into the A ports, it was clear that there were no catastrophic backfires or explosions. However, the thing was compromised by the fact that the DCI was open to the cylinder during transfer opening period, but towards the TDC position the port communicated with the crankcase because of the piston skirt cutaway. So the poor old pressure waves inside the passages didn’t know what to and if they didn’t know, then I certainly didn’t.

Fortunately, the B ports were masked off by the piston skirt in the TDC zone, meaning the DCI passage only connected to the cylinder in the transfer open period (see pic). So, the B ports it is.

Lots of filling and cleaning up inside the passages to go, plus crankcase stuffer pieces as can be seen on the A port cylinder.

Might have it running in a couple of years.