A BIT OF SIL 200 TUNING

[Darrell Taylor]

Recently had a sil 200 cylinder and head in to tune for touring use with a reed valve conversion running on a 30mm carb the brief was for excellent tractability with a low rpm peak
The cylinder was coupled with an asso 1.5mm ring piston so the port widths were kept mild so nothing extreme in its layout which comprised single exhaust port 2 transfers and a single boost port was added
the porting layout is very simple in appearance but accurate in respect to port durations ,areas and angles its exhaust port/inlet port and base gaskets are all to standard gasket sizes.

[Darrell Taylor]

the barrell fins were cut away to suit the mb reed assembly that runs the great little derbi reed block that i reccomended (its not minarelli as advertised) and the 30mm pwk that i run on my zip and derbi race motors matches the reed size really well


I matched the reed box to the inlet port initially with a fine finish then returned to rough it up






the cylinder head was standard so machined it up to a slightly higher compression ratio

[Darrell Taylor]

had to trim out a corner of the reed box to allow full petal lift and stop the petal from breaking its tip where it touches down too early

[Darrell Taylor]

heres the piston window i added

[Darrell Taylor]

top view of the simple port layout

[Darrell Taylor]

view from base

[Darrell Taylor]

ex port

[Darrell Taylor]

The results from dyno testing was ok as the power when fitted with a temporary af clubman was quite good/promising and for a sil 200cc fares quite well against a few of the off the shelf kits
15.66 bhp 13.4 torque

[Darrell Taylor]

a return trip with a new pipe fitted (ads3) had the motor running lean so richened it up and running a rich 11.5-1 afr showed some better results
21.7bhp and 18 torque

power range
4k 6.7bhp
5k 12.3bhp
6k 20.3bhp
7k 21.7bhp

[mickdale]

hello darrell,
would you recommend a 30mm pwk on a non reed converted SIL200 top end?

cheers
mick