Author Topic: SR175 ports  (Read 1286 times)

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Offline dcX

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SR175 ports
« on: August 23, 2023, 04:47:35 PM »
Are the inlets & exhaust ports the same (or different) on the SR175 compared to a DT175.

I'm getting my DT cylinders relined (cast iron liners) so have the opportunity to have the port layout I want, if the SR175 ports are different (more power) then I'll go down that route. With the caveat that someone will kindly share port details: photos / dimensions / layout / diagram.

Many thanks

Offline SR-175

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Re: SR175 ports
« Reply #1 on: August 27, 2023, 04:34:27 AM »
Hi Dave,

In the downloads section of the site you will find - "Tuning Up For Competition" - This might help with the details you are looking for.


Offline anotheroldtrailrider

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Re: SR175 ports
« Reply #2 on: September 30, 2023, 04:41:06 PM »
Although mine's a 200, I'm looking for port dimension/degree timing for a stock cylinder, as well as for modified engines.  I have the "tune up for racing" manual, but although it shows (now somewhat outdated) port mods, it doesn't give the actual dimension from the top of the cylinder or the crank degree position.  Once I have a good feel for which port/chamber combo's produce which power bands, I can decide on the best compromise for my little Ozark mountain road playbike.  Anyone have port top and bottom dimensions from the top of the cylinder they can share?

Offline OldSwartout

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Re: SR175 ports
« Reply #3 on: October 02, 2023, 06:01:53 PM »
I found some of my notes from 2008, the SR175 port distance from the top of the cylinder was Transfer 36.81mm, Boost 34.69mm, Exhaust 26.14mm.

A word of caution, DO NOT exceed 11,000 RPM. If you run above that for even short periods of time, two things will eventually happen.  The crankshaft center pin will fracture from rotating bending stress and the stock piston rings will fracture into pieces, eventually snagging a port.  Design and build your chambers to peak around 9-10,000 RPM or a little lower and get a working tach to keep an eye on the RPM.  There are digital tachs that work reasonably well.

Some of us ended up using Wiseco Suzuki RM80 +.050 pistons to fix the ring problem. Paul Piskor has a fix for the crankpin, but it's not really cheap.
Karl Swartout
Mooresville, IN
BS175 Roadracer. BS200RS, BS350 GTR



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