Forum > 50, 60, 90 & 100 Talk

top speed on the 90cc standards and sport version

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buddy rawls:
OK guys, the bike is tuned to spec, fresh plug, ,good oil, and now a fresh clutch.  I am getting a top speed, in optimum conditions, right around 58-60 mph.  Is this about what can be expected with them in antique, but freshly tuned condition?

When I checked my gearing, it had already been swapped 1 tooth larger on the front (15/34).  However, I dont think the motor is responding as favorably with the higher gearing.  I am actually thinking dropping back to the original gearing (14/34) may respond with identical top end, yet with a stronger midrange.  The original 65mph top end of the sport 90 was done with stock gearing.  albeit a new fresh bike.

Anyway, as it stands, the bike can cruise very nicely in the 45mph region, and if conditions are absolutely perfect hit right around 60mph?

So, is this about what everyone else is getting on their 90cc bikes.

Next,  I am a custom camshaft designer (valve event calcs, etc).  I am thinking about messing with the rotary valve timing, but not necessarily for the increased rpm of the B/S perf book, but simply for a better cylinder fill and cylinder pressure (increased torque and midrange) to bring a broader powerband to the bike.  If anyone has a motor disassembled, let me know; there are measurements I would like to get so I can figure cross-sectional areas, and then approximate flow potential to calculate the intake timing points in conjunction with piston position relative to the exhaust diameters and lengths.  2 stroke stuff is pretty bizarre, when you are super focused on V8 4-strokes.

ztnoo:
You can find the disc valve timing specs for 90s here: http://bridgestonemotorcycleparts.com/index.php?action=downloads;sa=downfile&id=18
The specs are on page 23.

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