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Old 02-01-2013, 06:23 AM   #134
JMo (& piglet) OP
Gone a bit Baja
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Joined: Apr 2007
Location: Somewhere west of Laramie...
Oddometer: 4,444
Originally Posted by mtrehy View Post
Hey John...

...Sounds like you have good people involved so I'm sure it's all been considered. If you haven't done so already i'd happily run it through some simulation if you can give me the port dimensions and flow details - must be readily available for the 690.

Are there enough potential customers to recoup your investment time and costs?
Hi Mtrehy! - many thanks for your offer of running a few simulations... as you suspect, things are going to be tight in there, and it is not just the physical elements of everything meshing (but hopefully not actually) coming together, but how it effects the power characteristics...

John has already been talking with the development department at Cosworth* regarding the dimensions required, and they will actually be laser-scanning a stock 690 head on Monday, so that we have the most accurate data available.

After John's original meeting with them last year, they are confident it can be made to work - but as you suggest, how efficient and ultimately how suitable the new engine characteristics are going to be, is very dependent on getting a prototype engine running and in a bike...

*Regarding your final question - while it is true there is only going to be a limited market for a complete 450cc conversion kit for these engines, the development spin-off is the ability to create a separate profile for a stock replacement and hi-compression piston option for the regular 690 engine (to be machined from the same batch of blanks, hence the desire to keep the original 690 bore and pin centre) which as you might imagine, has a far broader commercial application - with aging 690s in Enduro, SMC and Duke guises, or anyone looking for higher performance from the original capacity engine.

Should the initial prototype prove sufficiently successful, then it is likely that Rally Raid will be producing a batch of regular 690 pistons (in stock and hi-compression ratio) in conjunction with Cosworth, together with the required number of 450cc piston profile.

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