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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Tracking, Autocrossing, Dragstrip, Driving Techniques > When to Shift Discussion--The right RPM



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      09-21-2010, 06:12 AM   #23
Clap135
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1st gear is so short that it doesnt even matter that much. How are you even able to judge when to shift out of first in a fully bolted car? You actually have traction?
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      09-21-2010, 05:56 PM   #24
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Just to let you guys know, I'm going to a flat stretch of road today and I'm going to try the same test is previously with the Vbox to measure the Gs.

I'll try to do 1st gear pulls, 2nd gears pulls, and 3rd gear pulls...2 of each.
I think that the most interesting gears are the higher ones but it's hard to hit 100+ MPH on streets around here.
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      09-21-2010, 06:44 PM   #25
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Why is this sticky'ed when its nowhere near accurate?
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      09-22-2010, 08:56 AM   #26
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Alright guys, here is what I got from my logs:
I did about 3 runs in each gear on the same stretch of road and looked at the logs.

At redline in 1st gear I was pulling the follwing Gs at redline:

.59
.59
.54

At the same speed of at redline, I went WOT in second gear and pulled the following:

.60
.60
.57

The Gs before redline in 1st gear is higher than the Gs at redline, so if I were to shift before redline, I would be loosing acceleration.

Let's look at the results from the redline area of 2nd.
At redline in 2nd gear I a was pulling the follwing Gs at redline:

.39
.39
.37

At the same speed of redline (2nd gear), I went WOT in third gear and pulled the following:

.46
.42
.44

Notice that the acceleration in 3rd gear is greater than redline at 2nd, so I went down the curve and found the speed of where the acceleration on the end of 2nd gear matched the acceleration of the speed in the next gear.
The speed which I should shift is approximately 67 MPH.
67 mph with my setup is approximately 6750 ish RPM.
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      09-22-2010, 09:17 AM   #27
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Still flawed. You need to actually shift and record different shift points. Doing stationary pulls and comparing gs is not accurate.
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      09-22-2010, 09:23 AM   #28
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Quote:
Originally Posted by Clap135 View Post
Still flawed. You need to actually shift and record different shift points. Doing stationary pulls and comparing gs is not accurate.
Laloosh,
Insead of making statments of how wrong it is, prove otherwise and then I will look at your data.
Unless YOU have data to prove otherwise, I'll just say that YOU are wrong.
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      09-22-2010, 09:42 AM   #29
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Quote:
Originally Posted by Clap135 View Post
Still flawed. You need to actually shift and record different shift points. Doing stationary pulls and comparing gs is not accurate.
Then he does that and you're going to ask for him to test it on concrete asphalt and dirt, oh and then on all of the above but patches of sand and oil, then with different tires, and a short shift kit, and lsd...

Just step off, the data is good and empirical.
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      09-22-2010, 09:44 AM   #30
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1. Shifting does not maintain the same gs at xxxx rpm as simply pulling through that range.
2. Same goes for boost.
3. You like your data.....that's nice. However making people believe its true is hurting the community.
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      09-22-2010, 10:11 AM   #31
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Quote:
Originally Posted by Clap135 View Post
1. Shifting does not maintain the same gs at xxxx rpm as simply pulling through that range.
2. Same goes for boost.
3. You like your data.....that's nice. However making people believe its true is hurting the community.
He's not trying to pinpoint the EXACT rpm to shift at, simply that shortshifting around X rpms would yield peak acceleration VS running it through redline (referring to the higher gears).

God whats the point of being a mod if you can't ban asshats?
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      09-22-2010, 10:14 AM   #32
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Quote:
Originally Posted by Clap135 View Post
1. Shifting does not maintain the same gs at xxxx rpm as simply pulling through that range.
2. Same goes for boost.
3. You like your data.....that's nice. However making people believe its true is hurting the community.
You just further proved that I'm right.

1. Once you shift, it takes time for the acceleration to build so the acceleration at the same speed in the next gear will be even less than the previous gear.
2. Again, boost will take time to go up to peak so the gs when shifting into the next gear will be less than pulling through the range.
3. Wrong. It's only hurting you.

I don't care what you say, the Gs at the end of first will always be higher than at the same speed in second. I proved it.
Again, prove me wrong with your data.

You can't go with only comparing 1/4 mile times. Shifting times vary.
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      09-22-2010, 10:22 AM   #33
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Prooved you right? On what grounds. Log gs through a full pull while shifting. Post shift there will be a spike if your car doesn't bog due to the tune or clutch ect ect. Winding out the first two gears is common sense cause they are short. Its the later shifts that are more important.

For the other guys making asshat comments. If the point of this thread is not to. Find specefic shift points then what is the point? Read much? He's actually saying not to short shift. Nice effort.
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      09-22-2010, 10:51 AM   #34
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Spikes will happen at any shift point.
I'd rather have a spike at a point where at a higher g than a lower g.
If shifting early, the spike will happen and fall at a lower g than shifting later.

EDIT
Wait a second,
Now you are saying that winding out the 2 gears is common sense?
Man, you are all over the place.

Quote:
Originally Posted by Clap135 View Post
Winding out the first two gears is common sense cause they are short. Its the later shifts that are more important.
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      09-22-2010, 12:04 PM   #35
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How am I all over the place. I never stated where to shift. I stated your synopsis theory was inaccurate and your g theory doesn't take all the variables into account.
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      09-30-2010, 08:05 AM   #36
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Notice the power through the gears on a n54. This is a DJ dyno....same type you used that doesnt even load the car up properly



Your tq curve theory is prooved to be flawed. You other theories of using G's well I guess we cant discuss those untill you actually do a couple shifts going from 1st to 4th at different shift points. You need to actually SHIFT not match up speeds in different gears.

Last edited by Clap135; 09-30-2010 at 08:10 AM.
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      09-30-2010, 09:19 AM   #37
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This doesn't prove I'm wrong.
This doesn't take into account the multiplication of each gear ratio and that dyno is trying to normalize the power.
This is why we see the numbers we do instead of seeing 12,000+ ft lbs to the wheels.
Sorry, try again.
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      09-30-2010, 10:35 AM   #38
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Quote:
Originally Posted by Mr. 5 View Post
This doesn't prove I'm wrong.
This doesn't take into account the multiplication of each gear ratio and that dyno is trying to normalize the power.
This is why we see the numbers we do instead of seeing 12,000+ ft lbs to the wheels.
Sorry, try again.
I understand how gear ratios work. However you seem to not grasp the idea how power curves work based on loads on the engine. Apply your gear correction factors when you actually have a graph of htat gear. You cannot apply 1st gear correction numbers to a 4th gear power curve. Sorry, Try again.
Like stated by me and others. There are TWO ways to figure out the optimal shift point for your car.

1. Do a 1/4 on a mustang dyno and apply gear correction factors. You can't simply use a one gear pull as it is not accurate and will not remain constant through an entire run.

2. Do the same on the road while logging with a g meter. Log a couple different shift points and see what gets you the highest overall number. You need to actually log the shift.
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      08-15-2012, 04:41 AM   #39
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ok just a quick question, i found this topic and thought maybe somebody here can help answer my question since i really am confused.

i own a 2007 330D SE Coupe (245bhp) and i am wondering what is the most efficient gear changes i can do to save the most fuel consumption? i been sticking to low rpm and high gear changes but i still find my self doing really low MPG, please any advice is wellcome
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      08-20-2012, 06:46 PM   #40
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Best shift points on a FBO JB4?
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