If you race while leaving it in D, you should try using manumatic

the car doesn't let off the throttle for as long-- in D it almost stops, or so it feels

I found mine best to have it shift about 100-200 rpms before the redline

 

yes i agree. your shift point sounds very logical to me. have you tried it on the 1/4 mile track or just road testing?

 

As brought up in another thread, I was wondering what is the best shifting points through each gear for the best straight line speed. I used to this "kissing" the redline is the best method for our G, but that thread had made me think other wise.

Here's a generic response to your question that's not restricted to an auto tranny. To find the best shifting points in any car you need to get the torque curve for your engine. The idea is to stay in the sweet spot of your torque curve as long as possible. This does not necessarily mean that you shift when you hit your maximum torque, and you may go all the way up to redline even though there's a decrease in torque as you approach redline.

The reason is that when you shift into higher gears, you are going to lose about 2K RPMs. So if you shift at 7K RPM which is well past your max torque, your shift may take you down to near the maximum point of your torque output, of course depending on the car you are driving. So check your torgue curve to determine where you have the best power range available, and then select your shift points accordingly.

It just so happens that for many performance cars the best shift point is just a tad below redline. Under no circumsstances of course, do you want to bounce off the rev limiter since that will cut your power.

 

u made a good point fast1, at least to me. Now, any car will have the best acceleration if stayin within the highest portion of the torque curve, how about the HP curve? Do I have to take that into consideration?

 

Yea at least indirectly. Here's the formula for HP: HP = Torque X RPM / 5252.

So by this formula if I have two cars that produce the same max torque, weigh the same, and have the same gearing, the car with the most HP will be faster. Why? Because the car with the higher HP will be able to sustain that torque at higher RPMs.

Here's an example courtesy of Bruce Augenstein to help illustrate the point:

A very good example would be to compare the current LT1 Corvette with the last of the L98 Vettes, built in 1991. Figures as follows:


Engine Peak HP @ RPM Peak Torque @ RPM

------ ------------- -----------------

L98 250 @ 4000 340 @ 3200

LT1 300 @ 5000 340 @ 3600


The cars are geared identically, and car weights are within a few pounds, so it's a good comparison.
First, each car will push you back in the seat (the fun factor) with the same authority - at least at or near peak torque in each gear. One will tend to *feel* about as fast as the other to the driver, but the LT1 will actually be significantly faster than the L98, even though it won't pull any harder. If we mess about with the formula, we can begin to discover exactly *why* the LT1 is faster. Here's another slice at that formula:
HP = Torque X RPM / 5252

If we plug some numbers in, we can see that the L98 is making 328 foot pounds of torque at its power peak (250 hp @ 4000), and we can infer that it cannot be making any more than 263 pound feet of torque at 5000 rpm, or it would be making more than 250 hp at that engine speed, and would be so rated. In actuality, the L98 is probably making no more than around 210 pound feet or so at 5000 rpm, and anybody who owns one would shift it at around 46-4700 rpm, because more torque is available at the drive wheels in the next gear at that point.
On the other hand, the LT1 is fairly happy making 315 pound feet at 5000 rpm, and is happy right up to its mid 5s redline.

So, in a drag race, the cars would launch more or less together. The L98 might have a slight advantage due to its peak torque occuring a little earlier in the rev range, but that is debatable, since the LT1 has a wider, flatter curve (again pretty much by definition, looking at the figures). From somewhere in the mid range and up, however, the LT1 would begin to pull away. Where the L98 has to shift to second (and throw away torque multiplication for speed), the LT1 still has around another 1000 rpm to go in first, and thus begins to widen its lead, more and more as the speeds climb. As long as the revs are high, the LT1, by definition, has an advantage.

 

wow. nice in-depth analysis. thanks

 

Was the 14.5 stock or with those mods you have listed? Looks like our cars are REALLY slow or those mods did nothing for you. Did you run the car stock ever? Times?

 

interesting, i also feel this whether its in our heads or not.

i would like to see 1/4 mile times with one in auto, one in mm and shifting, and one in mm but leaving it in 5th gear display and take the pass as if it were still in auto

side q: does turning VDC mode off actually improve performance?

 

Typically leaving the transmission in automatic shifting will achieve the best times. VDC hampering performance depends 100% on your tires/traction. If you waste time spinning your wheels then it can help but if you know how much pedal to use you will get better times with it off.