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?