[mattman419]

Just got my first RC and love the V-twin. This is a 2000 RC51 with '03 everything on it uncluding the motor. I have the origonal motor and was planning on building it. What performance mods should I incorporate in the rebuild? Should it be bored and what head work should I throw in there? I will be doing most of the work myself, all but the machine work. Will i have any problem hooking up the SP-1 motor to the SP-2 wiring harness and/or fuel injection? Any and all tips will be appreciated. I do want to keep the bike streetable.

Man I love the bikes sound and power. So much fun having this bike being a 4-banger owner my whole life.

[zerogara]

I'd look for HRC heads and pistons and use SP2 injection which is by far superior.
I don't think the bottom has much of a difference, the clutch I remember having some differences.
Reboring and replating is a major job, I think you can find a whole SP2 motor on eBay for less (problems & cost). I've seen them go for less than some late 600s. The Honda plating is a very unique compared to most others, which doesn't mean you can;t try a different process (look up LA Sleeve among others).
I don't think you want to try to go to a larger bore, not that you have much metal there to do so, but the motor is already oversquare. If you compare the MX 450s they range 95-97mm while the rc is at 100mm with shorter stroke. I'd research the possibility of leaving the bore alone and see if you can go 2mm up on stroke, which due to the design you must utilize equally/2 shorter rods, therefore higher piston speeds at equal rpm. But a longer stroke will give you a little more usable power with a bit off top end cut off, which the motor is already capable off but for safety and longevity is restricted.
As someone else on an other thread had pointed out to me as well, the stock pistons are 10.8 while the HRC are 12.8:1, but 0.3 comes from the heads having smaller squish volume than the stock head, so HRC pistons alone will only bring it up to 12.5. The port design on the SP2 is a bit better than the SP1 (O vs D).
If your bores are not scuffed I'd leave them alone. There are other aftermarket pistons you can use, I think Wossner makes them and are as good as gold.

RC51 100mm x 63.6mm 10.8:1
ktm 525 95 x 72 mm
'10 CR450 96mm x 62.1mm
Ducati
96 999S 100 x 63.5 mm 11.4:1
96 999R 104 x 58.8 mm 12.5:1
1,099 cc 104 mm x 64.7 mm 12.5:1
1,198.4 cc 106 mm x 67.9 mm 12.8:1
KTM RC8 1,148 cc bore/stroke: 103 mm x 69 mm

[mattman419]

Awesome info and gives me a lot to think about. The motor in question was sunk in Hurricane Katrina so the '03 motor in the bike is good and runs well. I was gonna make the '01 motor from Katrina and just make it a project motor since I has it sitting around. Gonna disassmble it next week and see what kind of shape the heads and cylinders are in. I actually used the clutches out of the sunk motor to get the '03 motor going so I figured they were the same when they worked out. When i look at the parts fiche all of the engine parts seem to have the same part # so I will check all the specs when I teat it down next week. (This was just a spare motor that came with the bike when I got it.)

Again, thank you for the info. Any and all info is welcome.