Big engine, little frame

[98ninja]

I keep hearing locals and others talking about putting a 900/1000cc engine into a frame for a 600.
I dont get the logic in this other than a smaller bikes frame might be tighter steering or lighter.
My understanding was that a bikes frame is made by the manufacturer to handle that engine and its power output.
What percentage of a bikes weight would be taken up by the engine alone?
Am I missing something here?

[Gosling1]

its been done for decades mate. Many many decades. Smaller bike frames are generally lighter with quicker steering geometry (not always, just generally). This is the attraction.

Chris Dowde squeezed a gixxer 750 motor into a GSX400 frame back in the mid-80's, for Rob Phillis. That bike was awesome in the superbikes series of the time. Back in the late 80's they jammed FZR1000 motors into 750 frames for a lighter better-handling bike.

I have squeezed a GPz1100-based motor into a z750 frame for Period 5. The z750 frame has better bracing and steering geometry compared to the 1100 frame. So this bike steers like a 750 and is much lighter. This type of mod is not uncommon at all.....whether for track or street use.

Not sure what 900/1000 motor would fit into a 600 frame though ? Maybe a CBR9/1000 into a CBR600 frame ? This could work - it all depends on clearances and chain run alignment. A 600 frame will easily cope with the extra power - may need some bracing etc if you hot the motor up ?

There are also a few examples of ZX9 motors being jammed into ZX750 frames. This is a pretty easy mod as well - at the end of the day, most frames are capable of dealing with extra hp, as long as suspension etc is set up properly.

[98ninja]

its been done for decades mate. Many many decades. Smaller bike frames are generally lighter with quicker steering geometry (not always, just generally). This is the attraction.

Chris Dowde squeezed a gixxer 750 motor into a GSX400 frame back in the mid-80's, for Rob Phillis. That bike was awesome in the superbikes series of the time. Back in the late 80's they jammed FZR1000 motors into 750 frames for a lighter better-handling bike.

I have squeezed a GPz1100-based motor into a z750 frame for Period 5. The z750 frame has better bracing and steering geometry compared to the 1100 frame. So this bike steers like a 750 and is much lighter. This type of mod is not uncommon at all.....whether for track or street use.

Not sure what 900/1000 motor would fit into a 600 frame though ? Maybe a CBR9/1000 into a CBR600 frame ? This could work - it all depends on clearances and chain run alignment. A 600 frame will easily cope with the extra power - may need some bracing etc if you hot the motor up ?

There are also a few examples of ZX9 motors being jammed into ZX750 frames. This is a pretty easy mod as well - at the end of the day, most frames are capable of dealing with extra hp, as long as suspension etc is set up properly.

Makes sense. Thanks