Re: Tuning Options - Am I asking for too much?
Posted: Wed May 18, 2011 4:49 pm
Jim has tested his mods on a dyno, he should have a chart to illustrate what can be done with his 'stage 1' tune, there is a copy on my photo bucket photo site, same user name as here. Look for the very faded dyno chart with a difficult to read list of advantages, this combines the before and after bhp and torque curves based on a 1981 RS. I doubt if the R90/s will be much different. Pretty good results without going down the sports camshaft route.
What you will notice is how much fatter in the mid range, the 'after' torque curve is, this does translate in a much nicer bike to ride on the road, you don't have to rev the guts out of it
One of the bigger costs in doing this sort of work, is mission creep, if you are going to make you bike work harder, then you will quickly want to include a top end overhaul to include items such as valves, guides springs, maybe pistons if they are worn. Jim recommends going down the dual plug route, so you will need coils and he uses a Boyer ignition.
Engine improvements will put extra pressure on the brakes and handling of the R90S so you need to ensure that all frame wheel bearings are good, think about the suspension at both ends, and that the brakes work better, ( the 13mm handlebar master cylinder seems to really work wel with ATE front brakes, with a very useful reduction in the wooden feel that I seem to remember).
My R90/6 has been tuned by Jim for midrange and efficiency, the spec includes dual plug, some minor cleaning up of the ports, modern pistons from motoren Israel, lightening of the flywheel, a full engine balance and a full strip and rebuild to include bearings shells seals, bead blast, deep sump etc etc, the cost was around £3k. I only got the bike mot'd today and have only covered 80 miles, so I cannot comment on how it works, apart from the smoothness of the engine. My current carb problem dates from an earlier rebuld that I did.
Hope this helps
My R90/6
What you will notice is how much fatter in the mid range, the 'after' torque curve is, this does translate in a much nicer bike to ride on the road, you don't have to rev the guts out of it
One of the bigger costs in doing this sort of work, is mission creep, if you are going to make you bike work harder, then you will quickly want to include a top end overhaul to include items such as valves, guides springs, maybe pistons if they are worn. Jim recommends going down the dual plug route, so you will need coils and he uses a Boyer ignition.
Engine improvements will put extra pressure on the brakes and handling of the R90S so you need to ensure that all frame wheel bearings are good, think about the suspension at both ends, and that the brakes work better, ( the 13mm handlebar master cylinder seems to really work wel with ATE front brakes, with a very useful reduction in the wooden feel that I seem to remember).
My R90/6 has been tuned by Jim for midrange and efficiency, the spec includes dual plug, some minor cleaning up of the ports, modern pistons from motoren Israel, lightening of the flywheel, a full engine balance and a full strip and rebuild to include bearings shells seals, bead blast, deep sump etc etc, the cost was around £3k. I only got the bike mot'd today and have only covered 80 miles, so I cannot comment on how it works, apart from the smoothness of the engine. My current carb problem dates from an earlier rebuld that I did.
Hope this helps
My R90/6