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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 22565 times)

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #190 on: Nov 09, 2018, 03:26:53 »
Question im going to be re gearing my exciter. Have you messed with different set ups?

I have done in the past, I think I ended up with 17-40.  But I will look more into it when the time comes.  I know there are online calculators that help you work out rpm at certain speeds with different gearing ratios.  I will be looking for max power output at around 170kph so I have the tip of the torque curve around the 100mph mark so this gearing will be very different to stock bikes.  I will also be hoping to have power to 10,000rpm as well.

While on this topic, I have studied the parts diagrams for both the SR250 and the XS250 gearbox's - the latter because it is a 6 speed!  From the diagrams I could tell they weren't compatible but I found a good deal on a whole set up on ebay so I bought it anyway, in the hopes of learning something or maybe even swapping some ratios.  I learned something for sure, but this idea is a dead end - just look at the differences in the photo - SR250 gearbox at top (most of it), XS250 gearbox at bottom (all of it).  Very different beasts!


Online der_nanno

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #192 on: Nov 09, 2018, 17:52:49 »
As a turbo-bike-builder... which s/c are you thinking about? AMR300 or have you found something even smaller?
Real freedom starts with the freedom of thought.

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Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #193 on: Nov 10, 2018, 10:53:36 »
As a turbo-bike-builder... which s/c are you thinking about? AMR300 or have you found something even smaller?

Nope, you got it!  I managed to source a refurbished AMR300 from alibaba.  It seems in pretty good shape.  I will draw up custom billet intake and outlet ports for it to bolt up to the SR carb and then the engine on the other side (with a plenum-ish thing).

Online der_nanno

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #194 on: Nov 10, 2018, 15:05:45 »
If you go draw through, you want as little plenum between engine and supercharger as possible... AMR300s are nice. In your case run it at roughly 1:1 and you should see about 3psi + a bit for the inefficiencies of the engine, so just about enough to make you lust for more and then go completely bananas on the boost level.  8)
Real freedom starts with the freedom of thought.

My Blog:
http://greasygreg.blogspot.co.at

My Mule TR1.1 build here on DTT:
http://www.dotheton.com/forum/index.php?topic=75458.0

My Turbo TR1.1 (XV1000) build here on DTT:
http://www.dotheton.com/forum/index.php?topic=72571

My XS Triple Sidecar build here on DTT:
http://www.dotheton.com/forum/index.php?topic=74211

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #195 on: Nov 14, 2018, 16:00:22 »
After being at the motorcycle workshop FOREVER (seems like vintage bikes here get very low prio) the tyres have finally been mounted on the wheels - and they look great.  These Avons can be mounted front or back and have a mounting/direction arrow to indicate which direction for which wheel (front or back).  Somehow, despite me writing in large text in permanent marker on the rim, the workshop managed to fudge this as well.  They were embarrassed and fixed it onsite for me while I waited.  So they should.

Anyway, next stop, rolling chassis! 

Offline Tim

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #196 on: Nov 14, 2018, 20:11:33 »
Awesome tires - nothing like a set of fresh wheels all ready and waiting.
"Quality . . . you know what it is, yet you don't know what it is. But that's self-contradictory. But some things are better than others, that is, they have more quality. But when you try to say what the quality is, apart from the things that have it, it all goes poof! There's nothing to talk about. But if you can't say what Quality is, how do you know what it is, or how do you know that it even exists? If no one knows what it is, then for all practical purposes it doesn't exist at all. But for all practical purposes it really does exist."

Offline hooligan998

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #197 on: Nov 15, 2018, 00:47:12 »
Ssssseeeexxxaaayyyyy wheels!