Two step and shift points

[GSJimbo]

Setting my GS1166 for the strip this summer and was wondering where to start on to set the (high and low) on the two step rpm's and I'm using a MC-2.. also what a good rpm to shift at....Thanks

 

[massakins]

I used the dyno information I had as a starting point for shift RPM. Launch RPM was a matter of trial and error, looking for the sweet spot between bogging the motor and blowing away the tire (or wheelying if on a no-bar bike).

Currently I launch at 7500 RPM, shift by ear at approximately 9750 RPM and have rev limiter set at 11500 RPM. Bear in mind this is for a turbo using a slick and wheelie bars though.

 

[RacingJake]

Depending on what gearing, bars and a slick. 6-7 K launch and shift around 9300 if running G cams. If you spin the tire on launch keep droping the rpm's until it hooks up but not bogg.

 

[rosco15]

I launch at 6800 - 7200 and I would shift around 9400 or so. I sequentially shift my bike. So first is at 9600. The rest of the shifts are 9500,9400,9300. I have a slick and bar bike also.

 

[lecroy]

Why don't you shift at a constant RPM?

 

[rosco15]

I tried it all up high and then all down low. If I shift them all up high it runs slower. If I shift them all down low it seems like first gear comes up so fast. So I went for the best of both worlds. I let first gear wind itself out a bit and then take some rpm out down track. It turns the shift light on right at the finish line.

 

[lecroy]

Your not the first person I have heard of doing this but I have never heard of a reason. So, let me ask you this. If your not changing any other parameters (timing, etc) as you change gears, isn't the peak point going to be the same? If so, don't you always want to shift at the peak point and adjust the gearing according?

I have also heard of people trying to shift by time. So many ideas. I will stick with RPM.

 

[rosco15]

I had a friend explain the math to me on this when I first started doing it. He figured out what rpm I was at after each shift. I think we figured out that it drops the most rpm when you shift from first to second gear. So the longer I let first gear go the higher the rpm was at the begining of second gear. Thereby keeping me up nearer the peak power as I go into second gear.

 

[RacingJake]

Forgot about the high side. Set the high side at least 500 rpm's above your shift point. That way if you are a little slow in shifting you won't hit the rev-limit.

 

[Sandy]

Rosco makes the point on shifting at different RPM's. I'm from a road racing background but the theory is the same. An example to help clarify this was with my FZ750. I don't remember the exact numbers but it goes something like this. As the revs approached the 11,000 rpm redline power would start to drop off and it made really good power at anything over 7,200 rpm. When running it out to redline in first and second gears the rpm would drop to around 7,500 rpm. When running out to redline in the upper gears (ie: closer ratios) the rpm would be dropping to around 8,000 to 8,300 rpm so I lowered my shift points to get down to the 7,200 to 7,500 rpm range. This kept the motor within its best power range. So you don't necessarily have run to redline in all gears to get maximum effective power. Of course this all depends on your specific setup.

 

[lecroy]

I agree with what you are saying about the RPM and the shift points. With my setup it is about double from 1-2 as 4-5. But what I don't understand is how this makes your E/T any tighter than a single RPM shift point.

 

[massakins]

Would there be any merit to the thought that the motor has more heat built up in it when the higher gears come around, hence making more power at lower RPMs than when it was in the lower gears? Also, as a devils advocate this time, time growth would encourage one to raise the shift RPM as you go through the higher gears, to prevent bogging from too low a RPM. Comments?