Dyno graph - suggest the next step please

[Knowledge]

There's always a danger in posting your own dyno graphs on forums, but here we go.



Whilst the scooter is fine to ride, when I punch this info into the gear visualizer, it looks like I will have huge gaps between the gears, even with a pacemaker box. The graph seems to highlight that the useful power range is too narrow (even if it is fine to ride....)

The engine is an SR185 barrel, a Cagiva Mito reed welded to the barrel (in a TS1 style), RD350 piston, 26mm Dell'orto and JL3.

I want to continue development of the engine, one step at a time. Possible areas for improvement are increasing the inlet timing (it is not currently 360degree) , adding a boost port from the inlet, increasing the carb size or swapping the carb for something bigger or more efficient.

Any thoughts on what to do first?

[DigDug]

Get a scanner so your graphs look half decent.

[drunkmunkey6969]

Air fuel looks lean on the chart?

[drunkmunkey6969]

Any thoughts on what to do first?

What inlet timing is it? Maybe just start with cutting the skirt/lowering the inlet to increase the timing, forget piston windows for now, and machine a boost port in. Should be a good starting point......

[Adam_Winstone]

What is nice is that peak BHP is at 6250, rather than 8250

[Knowledge]

Adam,

Yes, and the torque and bhp at peaking at roughly the same point.

It is no longer revving its nuts off, unlike the previous pipe, and finally I have some torque. I think what I am after is a wider, flatter peak to the power, or a bit of useful over-rev beyond peak power.

[Knowledge]

What inlet timing is it? Maybe just start with cutting the skirt/lowering the inlet to increase the timing, forget piston windows for now, and machine a boost port in. Should be a good starting point......

The RD350 piston has inlet windows, but they are well down the skirt, which means that at BDC, the windows are below the inlet port (and therefore shut). I guess if I cut a boost port from the inlet port into the top of the barrel (opposite the exhaust) I should get some advantage as the expansion pipe should be creating a negative pressure above the piston, which will pull-in fresh charge directly from the inlet/reed via the new port.

It might be interesting to dyno the engine with the new port cut (hopefully showing some improvement) and then increase the inlet timing by lowering the port or enlarging the piston windows, and dyno again.

The problem is doing these things one step at a time. There is always the temptation to fettle once you have the barrel off.

[corrado]

There is always the temptation to fettle once you have the barrel off.

And there's always the "if it ain't broke ............ "

[jason frost]

Raise the inlet so its 1mm below the rings at bdc, cut the piston so it clears the inlet at tdc. Cut the top as wide as you would go with the exhaust port, lower the floor and taper it from the top with nice round edges.

[eden]

Air fuel looks lean on the chart?

Very