ESE's works engine tuner

[Frits Overmars]

....Frits is also right about the synergistic effect of a port radius and a piston timing edge radius - this is another level of sophistication that obviously works, in theory and in practice as he has tested and proven this.
Then you have the logistical nightmare of shaping the head squish band to suit this.

Not a nightmare at all Wob. If you let the squish band follow the dome of a piston with a timing edge radius and you center the head insert in the cylinder bore, as would be good practice with a non-radiused piston, you will end up with a thin, sharp, vulnerable edge on the insert that is susceptible to overheating and detonation.
But the solution could not be simpler: do not center the head insert in the cylinder bore, but around a collar on the cylinder.



You could also center the head insert in a larger-diameter part of the cylinder, like this:

[ApolloMotoMoto]

So, part of the issue with PowerSeal ...failing... to accomplish the Nikasil plating I had originally planned for (redirected to Millenium now);

I ended up behind the race teams testing schedule, and we have riders flying across the country for the "official test" of these engines for our next race... Good times.

To make up some lost ground, we are going to do the test with the chrome bores, and then send those cylinder in for Nikasil replating immediately after the test.

I still have some leftover pistons from the last batch that I had configured for Caber F-Cast rings (Chrome bore compatible).

And now I am measuring these chrome bores to see just how lucky I am... (if I was planning to do this, I would have specifically asked for cylinders in the right size range for my pistons, in this case I told my partner they were all getting re-bored and re-plated so the bore size didnt matter.... heh)


I had initially spec'd a piston to wall clearance of 0.060mm / 0.0023" (52mm air cooled cylinder, cast aluminum, forged piston).

Wiseco says they have tuned their process to the point where their forged pistons no longer "need" extra clearance relative to a cast equivalent, for what that is worth.

The best I can come up with are 3 pairs of pistons/cylinders with 0.054mm / 0.0021" clearance.


Would you run a 52mm jug that tight?

What factors go into deciding "how tight is too tight" for a given engine combo?

Is there a "generally accepted" rule of thumb (that actually works...) that is merely a function of bore size?

[Wos]

So, part of the issue with PowerSeal ...failing... to accomplish the Nikasil plating I had originally planned for (redirected to Millenium now);

I ended up behind the race teams testing schedule, and we have riders flying across the country for the "official test" of these engines for our next race... Good times.

To make up some lost ground, we are going to do the test with the chrome bores, and then send those cylinder in for Nikasil replating immediately after the test.

I still have some leftover pistons from the last batch that I had configured for Caber F-Cast rings (Chrome bore compatible).

And now I am measuring these chrome bores to see just how lucky I am... (if I was planning to do this, I would have specifically asked for cylinders in the right size range for my pistons, in this case I told my partner they were all getting re-bored and re-plated so the bore size didnt matter.... heh)


I had initially spec'd a piston to wall clearance of 0.060mm / 0.0023" (52mm air cooled cylinder, cast aluminum, forged piston).

Wiseco says they have tuned their process to the point where their forged pistons no longer "need" extra clearance relative to a cast equivalent, for what that is worth.

The best I can come up with are 3 pairs of pistons/cylinders with 0.054mm / 0.0021" clearance.


Would you run a 52mm jug that tight?

What factors go into deciding "how tight is too tight" for a given engine combo?

Is there a "generally accepted" rule of thumb (that actually works...) that is merely a function of bore size?

We run wössner forged pistons that are plated with ptfe with clearance 0,05 in aircooled nicasil plated aluminium cilinders bore 54.

Wössner states the ptfe is a break in surface...but even after 50 hours it isnt worn off completely...only down the skirt you see pure aluminium...

Ring we changing half the time!

Grüße Wolfgang

[Sketchy_Racer]

Slightly off topic, but related to racing two strokes,

Those who used to work with the 250 and 500gp bikes, do you remember if they use oil pumps in the gearbox, and if so, do you think the main purpose was, lubrication or cooling?

Cheers,
Glen

[jato]

Testing my memory here but i recall when the TZ 250 first went to pumped gearbox oil there was a net weight saving as there only needed to be 5 or 600 mils of oil to keep the pump happy, and therefore the gearbox happy. the RGB 500 didn't have a pump but ran a heavy weight gear oil. other 500 gp bikes i believe all run pressure lube. if possible you should do so , heaps of benefits - slightly smaller/lighter gears that are well lubed take the place of heavier/bigger gears. the sliding gear slides easier during a shift as it slides on a "cushion" of +- 30 psi oil. if you have a wet clutch the oil (depending on design) can be getting flushed through taking heat with it so the clutch can be slightly smaller and still be durable. a trans oil cooler becomes a possibility too. it'll be a faster more reliable bike imo

[Viking]

Viking , may I suggest you join the EngMod 2T Users Group on FB, I am an Admin so can approve you instantly.
Looking at your sim screenshot, I see a few things.
It has very good superposition, but to me it could maybe be improved by increasing the diffuser depression early in the cycle below zero pressure ratio.
This can be achieved with a shorter/steeper header, and a steeper first diffuser section - these adjustments are seen as improved peak and overev power.
The rear cone plugging amplitude is impressively high, but a little narrow in width.
Maybe a slightly longer tailcone, with increasing multiple angles would help.
Is that rpm at peak power ?

Wobbly,
I´m allergic to facebook, but I can´t resist your invitation, so I will show up there some day.

Regarding superposition and shorter/steeper header and steeper first diffuser section:
Earlier depression seems to be a good improvement, so I buy that.
My engine is for a snowcross racing snowmobile equipped with a CVT-clutch,
so overrev power is not useful.
I might transform the gain made, to the front side of the peak in some way.

Regarding plugging amplitude:
Your suggestion will be tried in the future.
What width is prefered?

Regarding rpm:
Yes, the engine peaks at only 8000rpm.
Transfer and exhaust ports width are limited by the cylinder studs and crankcase interface surface.
Also experience made from earlier similar engines, that had the peak at 9600rpm was very
difficult to tune for various hard snow and muddy snow on the track.