Beodude123

Well, I couldn't find any dynos for the cars here, so it'll just be a general guide.

This is an article I got off another car forum, but it applies all the same here. I think it's always good to know when you should be shifting. This will take away any guesses you have as to what rpm you should be shifting at. Here is the article;

Optimal shift points
By Dave Lum - 10/22/98

Looking to get maximum effect out of your car when accelerating? Try optimizing the RPM's you shift your car at. If you're shifting at redline, you're probably not getting the best acceleration out of your car - in fact, the optimum shift RPM will probably be different for each gear. You can calculate the optimum shift points, but it takes two pieces of information : Gear ratios of all your gears, and a chart of your torque curve.

The trick here is to keep your engine in the meaty part of the torque curve, as your acceleration curve will match your torque curve - meaning if your torque peak is at 3000rpm, that's the RPM your car accelerates the hardest. How do you keep the engine in the best part of the curve? Shift when you will be at an RPM where the car will make more torque AFTER you shift than in your current gear. This may sound confusing, but I will give some examples to help demonstrate this. Gear ratio is important because you need to know what your RPM's will drop to once you shift. EXAMPLE : If you're at 6500rpm in first, you need the gear ratio to know what RPM that will translates to once you shift to 2nd.

Below is a torque curve for a fictitious engine :
Engine
Torque Gear ratio Now with your gear ratio in hand, figure out how many RPM's will drop going from 1st to 2nd. In this case, it'll drop by 1/3 (2:1 divided by 3:1). So shifting from 1st to 2nd at 6000rpm, it will drop to 4000rpm. This means you're going from 330ft/lbs (see chart - 6000rpm in 1st) to 220ft/lbs (6000rpm * .6666) = 4000rpm in 2nd). Not what you want - you want these numbers to be the same. How about 6400? 285 vs 240 - much better, but let's try 6800 : 210 vs about 250. Oops, too far. In this case, optimum shift point is between 6400 and 6800rpm for the 1-2 shift.

It works the same for each consecutive gear, as the shift RPM may be different for each gear. Below are graphs representing how it looks on "paper".
RPMS___Torque__3:1____2:1____1.3:1

3600____100____300____200____130
4000____110____330____220____143
4400____120____360____240____156
4800____125____375____250____163
5200____125____375____250____163
5600____120____360____240____156
6000____110____330____220____143
6400____95_____285____190____124
6800____70_____210____140____91
Gear -->_______1st____2nd____3rd


Notice anything? The two torque outputs are almost the same (6600 in first and 4400 in second), which is what you're going for to achieve maximum acceleration. What does it look like on the horsepower side? Take a look at the chart below :







Well what do you know! You bracket the HP peak. HP after the shift is the same as HP before the shift. Now we know shifting at the torque peak isn't the answer, and neither is shifting at the HP peak.

The math required : next higher gear ratio / current gear ratio (i,e. second gear divided by first) = X

X * shiftrpm = nextrpm, where shiftrpm is the point your shifting AT, and nextrpm will be the RPM of the next gear at the same speed.

firstgeartorque = torque at shiftrpm times current gear ratio (example, at 6400rpm we have 95ft/lbs, multiply this by our gear ratio in 1st (3:1, or just 3) and you get about 245ft/lbs.

secondgeartorque = torque at nextrpm times next gear ratio (in out example, we have 120ft/lbs @ 4400rpm, times 2:1 (second gear ratio), and you get 240ft/lbs.

Change shiftrpm until firstgeartorque is equal (or close to) secondgeartorque.





I did all the math for a close to stock torque curve, and most of the mods won't change the shape of the graph that much anyways. Of course those with FI will have to change their numbers around.

Our gear ratios are
1st 3.76
2nd 2.269
3rd 1.645
4th 1.187
5th 1.0

For my caclculations, I didn't use sixth, because it's faster than most go, and it's not useful for most motorsport. Besides, you would be shifting fairly low (probably less than 8K) from fifth to get there. Anyways, on to the math!

Shifting from 1st at 9,000 lands you at 5,670 in 2nd. Torque at 9,000 is about 105 ft lbs, and torque at 5,670 is about 130 ft lbs. Multiply 105 by 3.76 and you get a total of 394.8 ft lbs in first gear. Multiply 130 by 2.269 gives you 294.97 ft lbs in second gear.

Since you are making less torque in second gear than first, you want to shift into 2nd after 9,000. I didn't find a close to stock graph that went up to 9,500, so I don't know the exact rpm.

Shifting from 2nd at 9,000 lands you at 6,525 in 3rd. Torque at 9,000 is 105 ft lbs, and torque at 6,525 is about 127 ft lbs. Multiply 105 by 2.269 and you get 238.2. Multiply 127 by 1.645 and you get 208.92.

Shifting from 3rd at 9,000 puts you at about 6,500 in 4th. Torque at 9,000 is 105, torque at 6,500 is about 127. Multiply 105 by 1.645 gives you 172.7 ft lbs. Multiply 127 by 1.187 gives you 150.75.

Shifting from 4th at 9,000 rpms puts you at 5,472 in 5th. Torque at 9,000 is 105, torque at 5,500 is about 130. Multiplying 1.187 by 105 gives you 124.6 ft lbs. 5th gear is 1:1, so at 5472 torque is at 130.

So for a stock car, you would want to shift above 9,000 for all gears except 5th and 6th. If you have any mods that are going to move your shift points up, then you'll have to shift even later. I don't think there are that many that make much of a difference though.


The above example was for an RX-8. All you have to do is plug in your own numbers. It's pretty easy to do. Since there are a bunch of different engines on here anyways, it would take too long to do them all. Hopefully this will help you guys though!