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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 3172 times)

Offline jpmobius

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #20 on: Aug 29, 2017, 17:56:14 »
Aerodynamics will be of critical importance with this much power to attain 100 mph.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #21 on: Aug 29, 2017, 18:15:12 »
Is it even physically possible to get 30hp out of these? Staying tuned..

Dunno man, but will sure as hell try.  From this research I have done, I will be going down the path of many small improvements to make a well tuned whole, rather than one or two drastic changes.  I'll be working a lot on lightening the entire valve train - with the intention of coping with more cam and lifting the rpm ceiling 1000rpm so it pulls to 10,000.  Will increase cc's and compression as well.  More will be revolved along the way!

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #22 on: Aug 29, 2017, 18:17:12 »
Aerodynamics will be of critical importance with this much power to attain 100 mph.

Absolutely.  This will actually be more crucial than weight reduction and outright power.

That being said, I would like to try with minimal aero stuff.  At this early stage, I am hoping a good body position (clip-ons, rear sets, tank hugging) plus a small headlight faring (to throw a little wind over my helmet) might do.  But it will require testing.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #23 on: Aug 30, 2017, 18:09:04 »
I think I shared this resource on the other thread but here it is again:  http://www.klemmvintage.com/bighorntech.htm

Yes it is a 350cc 2 stoke, but the chassis - suspension and brake set ups are very interesting I have taken a lot of inspiration from what they have done.  I will be doing similar stuff  :)

I also purchased Tony Foales Handling and Chassis Design pdf.  It is super dense.  And a pretty hard read I thought.  I have picked up a few key points but otherwise, will not be going into extreme details like in there.  https://www.tonyfoale.com

I do know what rake and trail I would like and what ride height/eye to eye rear suspension I would like though.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #24 on: Aug 30, 2017, 18:11:41 »
I did some quick research and it seems like 30hp should get 160kph.  Some pretty nifty 250cc Ducati singles have done it!  http://www.motorcyclespecs.co.za/model/Classic%20Racers/moto_morini_250_gran_premio_1964.htm

Given, that particular model had a fairing, BUT could reach 140mph...

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #25 on: Sep 10, 2017, 06:11:57 »
I'll be doing a kickstart conversion on this bike too.  But many people just add it and have it as a compliment to the electric start.  I will be removing not only the starter, but also the many internal parts necessary to make it all work.  Some of these are even rotating mass = power sappers. 

I did a little exercise where I collected all the parts from the two different assemblies (from a spare engine I have) and weighed the two set ups.  The total weight savings will be around 2.5kg.  And that is just in the engine!  Then if I were to include the fact that the battery will be able to be half the size as well, there will be a few hundred grams extra savings there too.

Offline Alex jb

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #26 on: Sep 10, 2017, 10:33:52 »
Thorough work!

If you are re-wiring then you could dump the e-start wiring and swap the hand control for one without button, it all helps!




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Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #27 on: Sep 11, 2017, 01:26:37 »
Thorough work!

If you are re-wiring then you could dump the e-start wiring and swap the hand control for one without button, it all helps!


Good point!

Offline datadavid

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #28 on: Sep 11, 2017, 07:21:26 »
Dont install the kicker, start it with a roller!

Offline Alex jb

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Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #29 on: Sep 11, 2017, 11:51:37 »
Dont install the kicker, start it with a roller!
That's a man in a van following you to Starbucks to re-start you after your mochachocachino?! 


Joking aside, old Skool privateers used to bump start their bikes to dump the kick start shaft didn't they?


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« Last Edit: Sep 11, 2017, 11:53:23 by Alex jb »