The forum Gods must have been looking kindly upon me last night... replies from CB750 Cafe Racer Fan, Calj737 & Fun Jimmy... you guys rounded out my list of peoples threads/posts I've been reading (and learning from) the most
! Can't wait for Paulages to join the party lol
By using the 650 head and downsizing to the 550 exhaust, you are losing the benefit of the head. Stick with a 550 head, and have the performance porting done to it. Unless you plan to build a fire breathing monster off a 650 platform like Paulages did, it's not necessary.
You could bore the 550 with 61mm pistons, a MegaCycle 126-20 cam, Mike Rieck Stage 3 job, and crank work, and back it up with some Miluni or CR carbs and have plenty of bike to grin at.
Or proceed with the 650 platform and sell the MotoGP exhaust to another European buyer. It will sell quickly due to its high market desire and availability.
The first point is based on the premise of a stock 550 exhaust correct? What dawned on me last night, and this is likely a question I ought to pose directly to MotoGPWerks, is whether the dimensions of his pipe & header are similar to the stock 550 dimensions or larger. I would assume somewhat larger for better flow, but allow me to restate that I am an absolute novice to this entire topic but boy am I having a blast learning
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If the door closes on the 650 head idea, then the plan will be to build the bike pretty much along the lines of what you've laid out above for a 550 build (the M Rieck stage 3 job being the only thing I may have to forgo due to int'l shipping.. otherwise that would have been a done decision to send it to him, along with my money, happily lol). The craftsmanship of the MGPW exhaust is so impressive to me, and it took a lot of effort and waiting time to get, that I feel it'd be a shame to let go of, so it's likely to be a staple of the build... even if that means ditching 650 part related ideas and working with the 550 only.
After reading Paulages' hybrid thread, it seems like a LOT of finesse work to make the 500 or 550 lower mated to a 650 upper work together. I must be missing something, since it seems like simply dropping in a 650 motor OR a 650 with a Dynoman 674 kit is an easier solution. That with some custom 650 headers and pachow, you got some easy grunt in a 500/550 handling package! Kickstarter be damned!
It certainly seems like dropping in a breathed on 650 would be easier, but for some reason I want to go through this with my 550 engine, in part because I am learning so much based on the research it takes to consider the hybrid build option (and that's the motivating part that's made it fun so far although I've been wielding a pencil and paper more than a wrench lol). I also want to retain the kickstarter
. The somewhat rudimentary plan I came up with thus far was, if possible:
my stock 550 lower case (potentially with a 650 crank for increased stroke)
my stock 550 cylinders bored to achieve an optimal balance with any changes to the stroke
New pistons to compliment the above
a 650 head with port work
the 650 cam (or a mega cycle one suitable for my application)
If possible a way to retain 550 valve cover (I've read that this requires a degree of custom modification but can be done)
Somewhere in there timing components will come into play but I haven't gotten that far with my research. Carb setup seems to be pointing in the direction of Mikuni or CR units.
I wonder how different a juiced 550 is compared to a stock 650? ... as Don said, to mate a 650 upper end to a 550 lower takes some effort, and maybe not worth the gains?
It'd be very interesting to find that out... maybe someone with a worked over 550, who has experience with the stock 650's, will chime in.
