Shortstroke Build

Nice, that looks mean and fun.

Reminds me of the Ecosse TI I was involved in without the excess bling....[/quote]

Thank you! I've just looked at some pics of the Ecosse TI - what wheelbase does that have? It looks quite long, which is what I worked very hard to avoid - depending on the set-up I choose, mine comes out at about 1410 mm /55.5 inches.[/quote]

It was quite long -I don't recall the exact wheelbase anymore. But with it's main use as a bar to bar cruiser it should have been longer. With the supercharger it was rather wheelie prone.
 
jseng1 said:
Paddy_SP said:
Kvinnhering said:
What stroke did you use Paddy?
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I apologise if I've confused matters - I was referring to my HD sprint-hillclimb racer: http://www.foxonic.com/harley.htm which has a 3.812" stroke using Cosworth DFL pistons.
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Gorgeous, but how does that little gearbox hold up to 1,200+ccs?
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Thank you - the 'box is actually a heavy duty Quaife grasstrack jobbie with a 4-speed wide-ratio cluster. The main case is about an inch thick - I've only ever seen two of these - and I own the other one too! :D
 
A 4 speed wide ratio box might be OK if there are no corners. My take on road racing is that if you've got the gearbox, you have got the bike. Everything else is easy. The last Gilera 4 was seven speed close ratio. There is no way a bike with a 4 speed wide ratio box will be as good as the same bike with a close ratio 6 speed box, where there are corners involved.
 
acotrel said:
A 4 speed wide ratio box might be OK if there are no corners. My take on road racing is that if you've got the gearbox, you have got the bike. Everything else is easy. The last Gilera 4 was seven speed close ratio. There is no way a bike with a 4 speed wide ratio box will be as good as the same bike with a close ratio 6 speed box, where there are corners involved.
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I think you've missed the fact that this is a sprint-hillclimb racer - the 'box is perfectly suited for that job. Oh, and in case you've never seen one of our tracks, the corners vastly outnumber the straights...:wink:
 
johnm said:
Paddy_SP said:
Kvinnhering said:
What stroke did you use Paddy?
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I apologise if I've confused matters - I was referring to my HD sprint-hillclimb racer: http://www.foxonic.com/harley.htm which has a 3.812" stroke using Cosworth DFL pistons.
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Wow! That looks a little exciting !!! :twisted:
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Thank you - it is easily the most aggressive bike I've ever ridden - and that includes my owned-from-new 1993 Fireblade and my RSV1000-SP Aprilia WSB Homologation Special. On a good day it does 5 mpg, on a bad day 3 mpg (and that's British gallons, not the smaller American ones!). If you can stop the back tyre spinning, the top yoke tries to smash you in the face. When I left the start line I was never sure whether I'd see the finish line or the inside of an ambulance first...
 
I try to never knock somebody else's go, however to my mind any sort of racing should involve development of functionality which is ultimately transferable for general purposes. I don't understand drag racing. Even the salt is a bit beyond me.
 
acotrel said:
I try to never knock somebody else's go, however to my mind any sort of racing should involve development of functionality which is ultimately transferable for general purposes. I don't understand drag racing. Even the salt is a bit beyond me.
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You don't "understand" short straight line races from a standing start, or maximum speed tests?

Let me help you: they're trying to beat the other competitors.
 
acotrel said:
I try to never knock somebody else's go, however to my mind any sort of racing should involve development of functionality which is ultimately transferable for general purposes. I don't understand drag racing. Even the salt is a bit beyond me.
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I think that's where we will have to agree to disagree. For the factories, one can make the argument that racing can help improve the breed for their production bikes. But for the rest of us, racing is an end in itself. It's all about trying to continually improve both man and machine, whether it's quicker lap times at a road race or higher top speeds at Bonneville. There's no need for improvements there to translate to anything else.

Ken
 
acotrel said:
I try to never knock somebody else's go, however to my mind any sort of racing should involve development of functionality which is ultimately transferable for general purposes. I don't understand drag racing. Even the salt is a bit beyond me.
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I read that as 'All racing is fine so long as it's done my way'... :roll:
 
When somebody is creating a short stroke motor for a road racer, surely what happens in straight line racing is only relevant if the road racer becomes 'point and squirt ? I suggest there are two options in road racing. You can have a motor which is top end and extremely powerful with a bike which tends to run wide in corners and when you have got it around the corner, stand it up and blast down the straight. Or you can have a bike with slightly less power, and more torque low down - which tightens it's line in the corners and gets on the power earlier. If you have a look at the movie 'I,Superbike', it is interesting that two of the four manufacturers have 'point and squirt' bikes. In the corners the slower bikes seem to get around faster, and there are a lot of instances where riders knock each other off their bikes.
 
acotrel said:
I suggest there are two options in road racing. You can have a motor which is top end and extremely powerful with a bike which tends to run wide in corners and when you have got it around the corner, stand it up and blast down the straight. Or you can have a bike with slightly less power, and more torque low down - which tightens it's line in the corners and gets on the power earlier.
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I don't recall my rider running wide when he had lots of power. Mind you, that's probably why he won the 500 GP World Championship...
 
acotrel said:
When somebody is creating a short stroke motor for a road racer, surely what happens in straight line racing is only relevant if the road racer becomes 'point and squirt ? I suggest there are two options in road racing. You can have a motor which is top end and extremely powerful with a bike which tends to run wide in corners and when you have got it around the corner, stand it up and blast down the straight. Or you can have a bike with slightly less power, and more torque low down - which tightens it's line in the corners and gets on the power earlier. If you have a look at the movie 'I,Superbike', it is interesting that two of the four manufacturers have 'point and squirt' bikes. In the corners the slower bikes seem to get around faster, and there are a lot of instances where riders knock each other off their bikes.
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Its all relative, none of these "short stroke" motors are really all that radically short, and even then then they are not necessarily peaky monsters (people do ride 125 and 250 GP bikes pretty fast as well and they are peaky). I have a bike that is putting out 45Nm from 3000RPM to about 55Nm @ 6000 and that has a bore and stroke of 95x70.7 and that can be a real handful out of corners because it comes on so early
 
I think you will find that most two stroke GP bikes handle on the stable side of neutral when coming out of corners (naturally tend to run wide), and use wide back tyres. The danger with peaky motors is they easily give the hi-side. When the stroke is very short the power delivery tends to not be smooth, but comes on very suddenly. Combined with a bike which tightens it's line, it is a recipe for a crash. If you've got the 6 speed close box, slow handling and plenty of nerve, short stroke motor can be very good. However some bikes can be very vicious. With the long stroke commando motor and a two into one pipe, it is very unlikely the bike will kick the rear wheel out from under you then grip and stick you up into the air. It is all pretty much 'horses for courses'.
I might be talking like an expert, however whenever I've been bitten I usually know why.
 
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