LANCER wrote on 06/01/19 at 07:59:31:Are the recommended discs on a 600cc engine based upon current 600 engines ? The LS is NOT a current engine by any means, with the primary issue other than currency (big bore & short stroke with great ports) being the buggered exhaust ports. It does hamper performance a lot.
When I had a Supertrapp on my Savage I believe I had about 10-12 discs if I'm remembering correctly. It sure was not 18-20.
Anyone else out there running a S/P ?
How many discs ?
Al Baker was a Honda XL/XR 600 specialist and White Brother was Honda XL/XR 600 and Yamaha TT/XT 600 specialist so same air-cooled big single thumpers. When punching the Honda out to 640cc and the Yamaha out to 680cc more discs were needed.
Frank Nye has done extensive dyno testing with CRF230 and it needs 10 discs for sure. Honda XR250 needs 12 discs and guys with 270 strokers need 14 discs. The CRF230 engine is basically an XR200 engine with hemi head and only two valves. Assuming a similar VE math yields the following:
(650cc / 223cc) X (6,000RPM / 10,000RPM) = 1.75 multiplier
(650cc / 223cc) X (7,000RPM / 10,000RPM) = 2.04 multiplier
Therefore a 650cc needs 1.75 to 2.0 times the number needed by 223cc so 17-20 discs.
When I got my Yamaha SRX600 it only had 12 discs and it was stuffed up. I went to 16 discs and then 8 discs and open end cap. It got better every time. All the SRX600 riders are using 16-20 discs and that engine is very similar except for twin carbs and twin pipes (i.e., one per valve).
My buddy used to race GNCC on 1991 Honda XR600 and he used a stock engine with opened airbox and adjusted jetting and Rob Muzzy pipe and he also used 18-20 discs. All this work was done with direction by Al Baker's tuners.
I have old WB data and a big spreadsheet at home with all the SuperTrapp disc data and will share it when I get back...
All of the above is with respect to 4" discs, not 3" discs...