TrinaBabe

iTrader: (3)

Since there seems to be a lot of confusion in this area i figured I would explain:

First of all we will explain how power and gearing works hand in hand...

OK... this is a simple concept if you think about it correctly. Power is mass acceleration of time.... how fast can you move an object tells you how much power you make. Since that was obvious think about it in a car... which gear can you accelerate 20 MPH faster in.... 1st or 5th? Obviously 1st. Therefore, you are technically making more power in 1st than 5th. Yes the motor may be making the same amount of power regardless the gear but since we are shoving the power through the gearbox we are multiplying it (Or dividing it in high gears) by the gear, final drive and wheel/tire size. So far this should make plenty of sense. Now to figure out your true optimal shift points:

First of all you take your handy dandy dyno sheet (Or use someones that seems close to what yours would be). Now you have the "close" true output of the engine. We just need to figure out which gear you want to be in and when you want to be in it.

You will take you power at the motor and multiply it by your gear ratio (Since tire size will not change through the run we dont need it). Now plot all this on an excel sheet. You will see you make a WHOLE bunch more power in 1st than say 3rd. The idea is to find where the optimal shift points are though.... So here is a chart I made for a dummied down Evo:



That is assuming this for power input:
1k 50
2k 75
3k 150
4k 250
5k 375
6k 350
7k 325
8k 295
9k 280

As you can simply see if these power numbers were correct you would be best off by holding the gear as long as you dare to accelerate as fast as possible even though the motor is making almost 100 less 3k RPMs after peak.

Now this is more interesting for the people that think calculating the average power for both gears is the way to find the best... so to say you make sure you are in the power band in the next gear as well as the first one: If you look at this chart, assume around a 3k drop in RPM per gear.... even dropping that much you are still accelerating faster in the lower gear. Now it isnt by all that much so you would need to get a more accurate dyno chart to figure it out for your car but you get the point... it has alot more to do with gearing than it does power bands.

I hope this makes sense for people.... I will make a new chart that uses real numbers so you can see a real example in a little bit.

TrinaBabe

iTrader: (3)

PS: If you still dont get it think of it this way.... the gear ratio for 4th gear is 1.031.. that is why 4th gear matches the engine power very closely.... it is as close to direct drive as you could get (So it shows the power of the motor).

TrinaBabe

iTrader: (3)

Well I think I may have been too optimistic on that last chart holding the power long enough.. here is the chart made from Buschurs RS. I had to kinda guestimate the 8 and 9k power outputs but it should be very close:



Now in this case you can see his best shift points by figuring out the RPM drop from each gear. Roughly 3k from 1-2, 2.5k from 2-3, and 2k from 3 to 4.

Knowing all this you can draw a line that is 3k long from the second gear line to the 1st gear line, 2.5k from 3rd to 2nd, and 2k from 4th to 3rd. You will need to find the highest average power of the two lines to find the best point also.

TrinaBabe

iTrader: (3)

Im tired now but you can easily see without getting the exact numbers that his best shift points would be somewhat close to:

1-2 @ 8.3ish
2-3 @ 8k
3-4 @ 7.8kish

Again, you would need to obviously have a dyno sheet with the power to 9k... I guessed at his power for 8 and 9k but it should be pretty close.

TrinaBabe

iTrader: (3)

The reason the RPMs to shift at are different is because the gear ratios get closer as they get higher in our cars. The farther the gears are apart, the longer you need to hold it to make the most power to the ground at all times... with very short gears you would shift often making the most out of the powerband.... but then you need to take into account shift time into the equation and that would get complicated....

TrinaBabe

iTrader: (3)

I hope this all made sense to people that are curious. Ill map out a relatively stock car tomorrow just for fun.

FathouseFab

iTrader: (5)

Your pics did not show up.

Fathouse

djh

I know you're trying to make this intuitive, but power is never multiplied or divided by a set of gears. Ideally power is unchanged but we know some is lost due to friction. What's multiplied or divided is revs and torque. A set of gears is the mechanical equivalent of an electrical transformer. For gears if the revs are doubled the torque is halved, their product, power, is the same. For a transformer if current is doubled the voltage is halved.

The easiest way to get gearing, torque, etc. out of the picture is to plot your wheel power vs. road speed in each gear. Your acceleration is proportional to the wheel power divided by the speed. Unless you're RPM-limited at some point the wheel power you're making in, say, 2nd gear will start to drop off as the speed goes up while 3rd gear power will rise. Where the two curves cross is a pretty good shift point. You should be able to find plots like this in any motorhead book.

Dave

matt55

iTrader: (12)

Maybe Iam seeing something different , but thoes shift pionts are WAYYYYY off

From what i can remember there is a 1500-2000 rpm drop when i shift gears (ie 1-2 , 2-3...)

It looks to me like a 6500-7000 rpm shifts would be the best usage of the powerband (ie shift at 7k from 1st to 2nd and start 2nd at 5k and so on)

But thats a very nice graph

Ted B

iTrader: (6)

If you want to calculate shift points using physics and not speculation, use the Excel spreadsheet I've attached here. I've configured it for an EVO8.

All you need to do is insert your torque numbers from your dyno chart. The spreadsheet automatically calculates hp and mph/rpm in each gear.

You simply go to the Accel vs. mph chart and denote where each acceleration line crosses the next. Then go back to the data page and record the rpm where each optimum shift point occurs.

The attached chart uses my data as a template.

evolution888

I think the Excel sheet was awesome. Thanks.

gsujeff55

iTrader: (4)

nice post ted.

only arguement i have is when shifting to the next gear or holding it through the traps comes into play....shift time is not taken into consideration.

so for instance, if its optimal to shift at 7500 rpms or 119 mph in 4th gear....you will probably suffer a lower ET if you shift vs holding 4th out...again, thats if its close

Ted B

iTrader: (6)

That's why you have to be quick.

gsujeff55

iTrader: (4)

LOL doesn't matter how fast, time to shift > acceleration lost by holding out 4th gear.

again, only when its within a couple mph say (121 vs 124)

Ted B

iTrader: (6)

It boils down to how much speed is lost during the 4-5 gear change. IF several mph is lost, that means you'd need to hold 4th a little bit past the optimum shift point to get into 5th at the right spot. If that results in holding 4th to the end, then that's what you'd have to do.