- 05-03-04 08:29 PM #16
Re: Shift Points??????Originally Posted by GNSCOTT
I would have to agree (as well with globed70 above the post which I quoted).
Let HP carry you until you are just after the peak HP, then shift to land in the next higher gear around (or just below) the peak TQ so you use ONLY the optimum powerband (Peak TQ to Peak HP range of RPM's) in that gear. That would get you the most power delivered to the gears (+ rear end, etc.) and therefore to the ground.
P.S. If you want to drive like Miss Daisy (and I have done this and gotten 26mpg in my V - consistantly) you shift to the next higher gear at the LOWEST RPM possilbe (and almost never downshift - coast whenever possible)....
- 05-04-04 07:39 AM #17
Re: Shift Points??????
Here is a post regarding Shift Points I wrote back in my BMW days:
HP and Torque does start dropping well before redline on stock E46 (non M3) motors. HOWEVER, what makes the car accelerate is Torque measured at the REAR WHEELS - AND - torque, unlike horsepower, is multipled by gearing. So by staying in a lower gear you are multiplying torque more, giving more power to the rear wheels.
Once you shift your ENGINE torque probably does go up BUT you multiply it less because you are in a higher gear, thus your REAR WHEEL torque falls.
As a general rule, for max acceleration you should shift near redline. The exception would be if the gear ratios were very close together or the motors torque curve fell WAY off at high RPM. On my 323i stick I shift from 1-2 and 2-3 at 6500. 3-4 at 6300 and 4-5 at 6200. This is my best guess looking at the gear ratios and torque curves. With a Dyno and the gear ratios we could determine the exact optimal shift points.
TORQUE multiplies with gearing.
Lets say your engine torque is 200 at 4500 RPM.
Now lets say you are in 2nd gear and the ratio for second is 2.0 to 1
And Your rear end gear is 3.00 to 1.
Your rear wheel torque is 200 * 2.0 * 3 = 1200 ft/Lbs.
Now lets say you shift to 3rd gear and 3rd has a ratio of 1.6 to 1.
After you shift your RPMs fall to 3500 and you get MAX torque of 220.
And you are at the MAX torque RPM for your motor.
You rear wheel torque is 220*1.6*3 = 1056 ft/lbs.
SO YOU SEE even though your engine torque is higher at 3500 RPM your rear wheel torque is lower because you are in a higher gear. You need to stay in the lower gear even when engine torque is falling because if you shift the gear ratio multiplier overrides the gain you will receive in engine torque at a lower RPM. Shift at redline. Try it with a stopwatch both ways if you want proof.