Abgeschickt von RGregor am 09 Februar, 2004 um 11:13:00:
Antwort auf: compression r75/5 von Niels Hansen am 08 Februar, 2004 um 11:30:53:
Hello Niels,
a couple of years ago I mounted R90/6 cylinders on my R75/5 using the /5 heads. Up to now it works without problem (approx 30 kkm).
I investigated the R90 heads and found no difference to the R75's, only the outlet valves are 40mm compared to 38 on the /5.
I didn't have any pinging problems, so I guess the compression ratio is OK.
If you can compare the R75 and R90 cylinders you will find the reason why the compression ratio will not increase much. While on top of the R75 cyl. there is a narrow collar of approx. 90 mm diameter protruding into the head, the R90 cyl. are totally plain. This results in a larger combustion chamber with the R90's.
I can give you no guarantee, but on my bike it worked.
Greetings
Rudi