Who has a stock 2pg piston laying around?

[TheGDFP]

I'm sure it will turn tighter, but based on design, it'll peak near there, rev farther though.
Yamaha MX bikes of the era, with tuned pipes and 36-38mm carbs, peaked between 6500-7500.

[1989Marathon]

Originally Posted by TheGDFP

I'm sure it will turn tighter, but based on design, it'll peak near there, rev farther though.
Yamaha MX bikes of the era, with tuned pipes and 36-38mm carbs, peaked between 6500-7500.

Do you know who Gordon Jennings was? If not, I would recommend you find out.

[TheGDFP]

I memorized most of The Handbook in Jr High

[1989Marathon]

Originally Posted by TheGDFP

I memorized most of The Handbook in Jr High

Well, then you're ahead of the curve.
What can you tell us about "mean piston speed".

[TheGDFP]

I can tell you that it borders on irrelevant in a fairly low-rev heavy recreational vehicle, but if a person wanted to take advantage of the 4.4mm shorter stroke compared to the bikes, that they could.

And, there's a nice picture on pg120, of the poorly-placed 2pg boost port.
http://www.amrca.com/tech/tuners.pdf

And, that there have been substantial changes/improvements in 2 stroke development in the 42 years since his much-quoted book, or these dinosaurs we're chatting about.
Bell's book is a nice one as well.

[1989Marathon]

"Mean piston speed" is not irrelevant to anyone wanting to make power in a reciprocating engine, especially a 2-stroke. The higher the "mean piston speed", the more performance can be obtained from the motor.
You have done just the opposite by boring the motor out. That lowers the MPS, if you take the corrected values into account.

[TheGDFP]

Disclaimer: No one should be stupid enough to think they can ever approach the HP numbers on a modern MX bike, with their industrial-based drone engine, mmmm-K.

Area under the curve, not just the maximum the engine is capable of, is the goal of this project.

MPS is in the 'safe with forged piston' to over 12k, WAY beyond the envelope.

Modern 250 2 stroke single MX bikes are crowding 200hp/liter, and still in the 8500 rev range, and make eleventeen times as much power as a cart-lump.

The cylinder is old-tech, and decent power could be made up top at the expense of the rest of the curve. Look at mod RD350, H2, etc, and see what I mean.

[TheGDFP]

Or, take the same engine, 250 Polaris ATV, cousin to the EZGO, and extrapolate progressive variations in tuning package.

[1989Marathon]

Originally Posted by TheGDFP

The cylinder is old-tech, and decent power could be made up top at the expense of the rest of the curve.

That's exactly right. You aren't working with a newer design so the graph is irrelevant. You aren't going to even approach those numbers with an older design.

[1989Marathon]

Originally Posted by TheGDFP

Or, take the same engine, 250 Polaris ATV, cousin to the EZGO, and extrapolate progressive variations in tuning package.

Does the Polaris motor have static ignition timing?