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How to get more power?
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It's always fun going faster!
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This discussion got me thinking about the HP2 series bikes with their 128hp air cooled boxer engines. I wonder if they had continued development of these how much more they could have squeezed out without reverting to water cooling.
![143018]()
There are some older threads in the forum that explore HP2 style performance gains for the R NineT - found one that linked this website which claimed 140hp at the rear wheel.
BMW R nineT by MotoKouture
If you are interested in engine design from an engineering perspective, the following technical article may be of interest - though not sure how practical it may be to implement these changes on our R NineT engines.
https://www.fsb.unizg.hr/miv/MSUI/K...The New Boxer Engine of the BMW HP2 Sport.pdf
If I recall correctly there are at least one or two owners of HP2 machines on this forum, @RJB
There are some older threads in the forum that explore HP2 style performance gains for the R NineT - found one that linked this website which claimed 140hp at the rear wheel.
BMW R nineT by MotoKouture
If you are interested in engine design from an engineering perspective, the following technical article may be of interest - though not sure how practical it may be to implement these changes on our R NineT engines.
https://www.fsb.unizg.hr/miv/MSUI/K...The New Boxer Engine of the BMW HP2 Sport.pdf
If I recall correctly there are at least one or two owners of HP2 machines on this forum, @RJB
@Joe-Rocket just found this for you:
Rizoma | Stealth Mirror
rizoma.com
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3,581 Posts
Yeah that looks pretty low, probably a drag bike and not a circuit lover. What i can’t see is how the exhaust ties in to run the turbofan ? Tesla’s going to come out with a bike that will eliminate all that hardware anyway ... the new name for gas bikes will be petro-sarous-wrecksOk, what’s wrong with that picture?
View attachment 142941
Find the mistake...
And then:
BMW NineT Forum
www.ninetowners.com
......Blitz
YES you can rebore the cylinders, NO you wont ruin them, there are many firms who re-nicasil cylinders in the UK. All motocross bikes have relied on this for years as have all the airheads that needed new pistons.
Maybe a better idea would be to have written " I DONT BELIVE Over size boring isn't an option, the barrels are Nicasil lined".
every day is a school day !!
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576 Posts
Searching the UK 'net you can get cylinders re-coated for as little as £155, but you still need a piston to suit, and multiply by 2..
I apologise for any miss-information, the guys I know that use 2 strokes for green laneing never bother when the cylinder gets scored/damaged, they say it's easier to just buy a new barrel and piston.
When I last looked, which is a very long time ago, it wasn't an option. Apparently a nicasil bore is supposed to last 3 times longer than a standard steel sleeve.
One other thing regarding a bigger bore is, in a lot of cases, you'll also need to do something with the valves, BMW will have made the valves as small as possible to save weight, that could be a problem.
All in, it's still a lot easier to tune a 2 stroke than a big 4 stroke and I'm happy with the100+ horses my bike has
HG
I apologise for any miss-information, the guys I know that use 2 strokes for green laneing never bother when the cylinder gets scored/damaged, they say it's easier to just buy a new barrel and piston.
When I last looked, which is a very long time ago, it wasn't an option. Apparently a nicasil bore is supposed to last 3 times longer than a standard steel sleeve.
One other thing regarding a bigger bore is, in a lot of cases, you'll also need to do something with the valves, BMW will have made the valves as small as possible to save weight, that could be a problem.
All in, it's still a lot easier to tune a 2 stroke than a big 4 stroke and I'm happy with the100+ horses my bike has
HG
i had a pair of R80ST cylinders re-nicasiled by Langport, near Weston super mare. bead blasted, bored to accept 94mm pistons, then coated, good job, many pf the racing fraternity use them. I have used nicasil ( or one of the many nickel-silicon-carbide variants) and don't find they last any longer than GOOD ductile iron liners, however its hard to accurately quantify as there are so many variables in that equation. One thing is for sure, IF the bore and honing is not done really well, any bore surface will not last well.
I have big bored many bikes, and left the stock valves in place, the smaller sized valves reach sonic choke at a lower rpm as the port velocity with larger pistons/cc is proportionally greater. this usually means more torque under the peak number, but not so much more actual torque. However to argue against this statement, I have bored, honed and fitted well over 200 Harley Sportster 883-1200 conversions, whilst keeping the stock itty bitty 883 valves, the 37% increase in cc actual yields far more than 37% more torque, all it does is limit the power as the torque drop off at 5500rpm+ is apparent. From experimentation the unshrouding of the valves gives some more flow capability for the same sized valve
I have also done a whole lot of Yamaha XS650 big bore conversions, to 750cc and up-to 880cc, using stock valve sizes, the HD experience is echoed in this engine too
To conclude, I believe from this, that big boring an R9T would give more torque right up to the torque peak, but maybe not increase the actual peak number by much. ( broader power-band) if I wished to tune an R9T it would be the route I would take, ( along with checking/correcting the squish clearance) you cant beat cubes you know !!
The valve seats can be properly recut, this optimises the discharge co-efficient of the valve/seat, there are many people who can cut superb race quality valve seats with machines like the SERDI 300 or the best a Newan Contour BB machine. a 5% increase in air flow, is not unusual whilst still maintaining high port velocity
I have big bored many bikes, and left the stock valves in place, the smaller sized valves reach sonic choke at a lower rpm as the port velocity with larger pistons/cc is proportionally greater. this usually means more torque under the peak number, but not so much more actual torque. However to argue against this statement, I have bored, honed and fitted well over 200 Harley Sportster 883-1200 conversions, whilst keeping the stock itty bitty 883 valves, the 37% increase in cc actual yields far more than 37% more torque, all it does is limit the power as the torque drop off at 5500rpm+ is apparent. From experimentation the unshrouding of the valves gives some more flow capability for the same sized valve
I have also done a whole lot of Yamaha XS650 big bore conversions, to 750cc and up-to 880cc, using stock valve sizes, the HD experience is echoed in this engine too
To conclude, I believe from this, that big boring an R9T would give more torque right up to the torque peak, but maybe not increase the actual peak number by much. ( broader power-band) if I wished to tune an R9T it would be the route I would take, ( along with checking/correcting the squish clearance) you cant beat cubes you know !!
The valve seats can be properly recut, this optimises the discharge co-efficient of the valve/seat, there are many people who can cut superb race quality valve seats with machines like the SERDI 300 or the best a Newan Contour BB machine. a 5% increase in air flow, is not unusual whilst still maintaining high port velocity
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