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      01-12-2013, 09:09 AM   #45
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Quote:
Originally Posted by dtc100 View Post
From a 335i guy.

Keep in mind it is not all about the curves. Even if the curve has fallen, keeping in the lower gear longer would still deliver more power to the wheels than switching to a higher gear, that is why there is this optimum shifting point that does not exactly follow the dropping curve.

As engine revs climb, Torque reaches a peak or plateau and then drops off. Some people think you should shift here. As revs climb higher, HP peaks and then drops off. Others think you should shift there. And others think you should always shift at redline. What's correct?

The key point is that you must consider tranny gearing AND engine T at different RPM when computing the best shift point.

Torque to the drive wheels = engine Torque * tranny gearing * axle gearing - drive train losses.

When you shift from 1st to 2nd, engine revs drop back into the power band of the engine and you get more Torque, BUT you loose the gearing advantage 1st gear had over 2nd gear. So the right shift point is when the engine puts out enough additional torque in 2nd gear to make up for the gearing advantage you had in 1st gear. If that doesn't happen, you shift at redline.

Here's the gearing for a 335i with 6MT:
1st gear 4.11
2nd gear 2.32

Can you see how it might make sense to stay in 1st year after T and HP have fallen off because of the huge difference between 4.11 and 2.32 gearing?

The Ideal shift point from 1st to 2nd can be computed if you gather the following info:

- engine T at different rpm
- 1st gear ratio: 4.11
- 2nd gear ratio: 2.32
- multiply 1st gear ratio by engine T at different RPM
- multiply 2st gear ratio by engine T at different RPM
- compute what the RPM drop would be when you shift from 1st to 2nd

If you did this, you could compare how much T is being delivered by the tranny output shaft in 1st gear and how much T you'd be getting at lower RPM in 2nd gear and see when 2nd gear's output exceeds 1st gear's output. There's your shift point. If 2nd gear's output never exceeds 1st gear's output, you shift at redline. If I had more time I'd do the computation and present it.

For most gasoline performance cars, the best shift point is redline. Just check the road tests in R&T, C&D, Automobile, Motor Trend and other car magazines. (Example: http://media.caranddriver.com/files/...ril-2012-1.pdf) Most manufacturers of performance cars build their engines to rev high because it's fun and it lets their cars stay in the lower gears longer to take advantage of the lower gearing.

Last edited by driverman; 01-12-2013 at 09:44 AM.
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      01-12-2013, 10:55 AM   #46
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Quote:
Originally Posted by dtc100
Quote:
Originally Posted by jopa489 View Post
Correct, in a 328i 6MT. Considering the auto in the 328 adds a good 1/2sec+ to 0-60 time, it looks like your car is pretty quick. Nice.
Guys with 6AT 328i's have consistantly shown 0 to 60 under 6, not any slower than MT. I have yet read as many 6MT 328i drivers reported their 0 to 60 time.
I've gotten a 5.8 with a GTech Pro multiple times with an Injen and powerbox on a 6AT E92.
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      01-12-2013, 11:28 AM   #47
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Car & Driver reported 0-60 in 5.9 back in 2010.

The 328i had ZSP and 6MT:

http://media.caranddriver.com/files/...powertrain.pdf

With ZSP, had the sport suspension and larger rear summer tires:

http://media.caranddriver.com/files/...ns-chassis.pdf
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      01-12-2013, 12:44 PM   #48
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Quote:
Originally Posted by driverman View Post
As engine revs climb, Torque reaches a peak or plateau and then drops off. Some people think you should shift here. As revs climb higher, HP peaks and then drops off. Others think you should shift there. And others think you should always shift at redline. What's correct?

The key point is that you must consider tranny gearing AND engine T at different RPM when computing the best shift point.

Torque to the drive wheels = engine Torque * tranny gearing * axle gearing - drive train losses.

When you shift from 1st to 2nd, engine revs drop back into the power band of the engine and you get more Torque, BUT you loose the gearing advantage 1st gear had over 2nd gear. So the right shift point is when the engine puts out enough additional torque in 2nd gear to make up for the gearing advantage you had in 1st gear. If that doesn't happen, you shift at redline.

Here's the gearing for a 335i with 6MT:
1st gear 4.11
2nd gear 2.32

Can you see how it might make sense to stay in 1st year after T and HP have fallen off because of the huge difference between 4.11 and 2.32 gearing?

The Ideal shift point from 1st to 2nd can be computed if you gather the following info:

- engine T at different rpm
- 1st gear ratio: 4.11
- 2nd gear ratio: 2.32
- multiply 1st gear ratio by engine T at different RPM
- multiply 2st gear ratio by engine T at different RPM
- compute what the RPM drop would be when you shift from 1st to 2nd

If you did this, you could compare how much T is being delivered by the tranny output shaft in 1st gear and how much T you'd be getting at lower RPM in 2nd gear and see when 2nd gear's output exceeds 1st gear's output. There's your shift point. If 2nd gear's output never exceeds 1st gear's output, you shift at redline. If I had more time I'd do the computation and present it.

For most gasoline performance cars, the best shift point is redline. Just check the road tests in R&T, C&D, Automobile, Motor Trend and other car magazines. (Example: http://media.caranddriver.com/files/...ril-2012-1.pdf) Most manufacturers of performance cars build their engines to rev high because it's fun and it lets their cars stay in the lower gears longer to take advantage of the lower gearing.
Thanks for the nice explanation. I was tempted to write a similar post but was too lazy to do so. Really, all one needs to know is the equation you wrote down, and the fact that the acceleration is directly proportional to the torque at the wheels, up to the correction from air resistance. It's just the rotational version of F=ma.
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      01-12-2013, 12:45 PM   #49
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Quote:
Originally Posted by driverman View Post
As engine revs climb, Torque reaches a peak or plateau and then drops off. Some people think you should shift here. As revs climb higher, HP peaks and then drops off. Others think you should shift there. And others think you should always shift at redline. What's correct?

The key point is that you must consider tranny gearing AND engine T at different RPM when computing the best shift point.

Torque to the drive wheels = engine Torque * tranny gearing * axle gearing - drive train losses.

When you shift from 1st to 2nd, engine revs drop back into the power band of the engine and you get more Torque, BUT you loose the gearing advantage 1st gear had over 2nd gear. So the right shift point is when the engine puts out enough additional torque in 2nd gear to make up for the gearing advantage you had in 1st gear. If that doesn't happen, you shift at redline.

Here's the gearing for a 335i with 6MT:
1st gear 4.11
2nd gear 2.32

Can you see how it might make sense to stay in 1st year after T and HP have fallen off because of the huge difference between 4.11 and 2.32 gearing?

The Ideal shift point from 1st to 2nd can be computed if you gather the following info:

- engine T at different rpm
- 1st gear ratio: 4.11
- 2nd gear ratio: 2.32
- multiply 1st gear ratio by engine T at different RPM
- multiply 2st gear ratio by engine T at different RPM
- compute what the RPM drop would be when you shift from 1st to 2nd

If you did this, you could compare how much T is being delivered by the tranny output shaft in 1st gear and how much T you'd be getting at lower RPM in 2nd gear and see when 2nd gear's output exceeds 1st gear's output. There's your shift point. If 2nd gear's output never exceeds 1st gear's output, you shift at redline. If I had more time I'd do the computation and present it.

For most gasoline performance cars, the best shift point is redline. Just check the road tests in R&T, C&D, Automobile, Motor Trend and other car magazines. (Example: http://media.caranddriver.com/files/...ril-2012-1.pdf) Most manufacturers of performance cars build their engines to rev high because it's fun and it lets their cars stay in the lower gears longer to take advantage of the lower gearing.
The math is nice & will put you in the ballpark but it does not include one very important variable Time. As RPM increases so does the amount of time it takes to gain additional RPM.

So in the case of a turbo with a redline of 7K vs. a shift point of 6K/6.3K pure math might suggest go at 7K. If the time it takes to get from 6K to 7K out weighs the mechanical benefits of a redline shift then you need to shift earlier.

Only two ways to figure this out. Various shift points at the same track on the same day or what the pros do with their onboard systems use an accelerometer to optimize the shift point.

A blanket statement that a red line is the shift point is problematic. A red line is the do not exceed this RPM line & can have nothing to do with the best shift point as demonstrated by the BMS factory cars 11.1ET's shifting at 6K.
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      01-12-2013, 12:53 PM   #50
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Quote:
Originally Posted by BEAR-AvHistory View Post
The math is nice & will put you in the ballpark but it does not include one very important variable Time. As RPM increases so does the amount of time it takes to gain additional RPM.

So in the case of a turbo with a redline of 7K vs. a shift point of 6K/6.3K pure math might suggest go at 7K. If the time it takes to get from 6K to 7K out weighs the mechanical benefits of a redline shift then you need to shift earlier.

Only two ways to figure this out. Various shift points at the same track on the same day or what the pros do with their onboard systems use an accelerometer to optimize the shift point.
No, that equation includes everything you need to know. Acceleration is defined as the change in velocity per unit time. "The amount of time it takes to gain additional RPM" that you speak of is simply another way of saying "acceleration".

So what you said can be summarized by one sentence: "At higher RPM the acceleration drops". This is the same thing as saying that at high RPM the torque drops off. This doesn't have to be the case, although for most engines it's true. So you are saying that sometimes the torque drops too much at high RPM that it could be preferable to upshift, thereby taking a hit in gear ratio but increasing the torque at the crank. This would be true if either the gear ratio is fairly narrowly spaced, or the torque drop is extreme. That's exactly what driverman's post explains.
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      01-12-2013, 01:17 PM   #51
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I should be doing other things, but my love for cars is trumping duty this morning.

I worked up some numbers to illustrate my point based on ROUGH APPROXIMATIONS of the N54's torque curve and a 6MT. Torque after tranny is T * gear ratio.

1st gear = 4.11
RPM T mph T after tranny
1500 250 8.4 1027
2000 300 11.2 1233
2500 300 14.0 1233
3000 300 16.8 1233
3500 300 19.6 1233
4000 300 22.4 1233
4500 300 25.2 1233
5000 300 28.0 1233
5500 280 30.8 1150
6000 260 33.6 1068
6500 240 36.4 986
7000 210 39.2 863

2nd gear = 2.32
RPM T mph T after tranny
1500 250 15.0 580
2000 300 20.0 696
2500 300 25.0 696
3000 300 30.0 696
3500 300 35.0 696
4000 300 40.0 696
4500 300 45.0 696
5000 300 50.0 696
5500 280 55.0 649
6000 260 60.0 603
6500 240 65.0 556
7000 210 70.0 487

In this example, if you wind out 1st gear to 7K, you'll have 863 lb-ft of torque on the output shaft of the tranny and you'll be going 39 mph. When you shift to 2nd, you'll drop down to about 4000 rpm and have 696 lb-ft of torque on the output shaft of the tranny. Therefore, even though T and HP are dropping off in 1st gear, you are better off revving to redline to take advantage of the shorter gearing 1st gear provides.

The same thing might not be true for other shift points. You have to run the numbers. A good cross check would be to see how far the car magazines rev the engines in each gear when they do their road tests. They are always trying to get the fastest runs.
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      01-12-2013, 02:46 PM   #52
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With all due respect the record holding stock turbo N54's both 135 & 335 shift at approximately 6K. Bigger turbos will push that shift point up with 6MT's but then there are issues with the autos at higher RPM. The shift point can vary a bit based on mods but the stock turbos are pretty much done at 6K.

If the math's 7K shift was the answer that's where they would be shifting since setting records for the vendors is money in the bank. I think these guys are smart enough if all it took to break into the 10ís was a small increase in shift points they would be quick to do it..

In this case the theoretical cannot be proven by real world performance measurements. Your results may vary but I am very lightly modified JB4 & 5" ETS FMIC running 12.5 X 114 with shift lights at 6200.

The car loses time when run to 7K. In addition to seeing the torque/horsepower fall quite clearly on dyno logs over 6K the drop in acceleration is so steep you can actually feel it in the butt dyno at the track.

Couple of old non-vendor dynos, gross power numbers are not important but the shape of the curve is because I don't think you will find a stock turbo N54 with a different shaped curve. Key to getting to the finish line fast is power under the curve.
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      01-12-2013, 07:28 PM   #53
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Quote:
Originally Posted by e87fan89
I wana know what you guys think of my 0-60, I timed it around 5.8~6 seconds.
I have an AA tune with bmw perf. exhaust and K&N filter.

Does the filter really make a difference? It's not very expensive, will buy if it really does make a difference.
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      01-12-2013, 10:57 PM   #54
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BEAR-AvHistory:

With all due respect (let's keep this friendly)...

I'm trying to reconcile the following:
- The points you made about real world performance runs
- Every road test I've seen on the 335i shifts at redline
- My analysis points to shifting at redline

Why would R&T and C&D shift at redline if it didn't yield the best result? Do they follow a standard procedure to always shift at redline? I doubt it. Don't they strive to get the best possible results?

Were the record runs you are referring to done with the stock 6AT or the stock 6MT? That could possibly explain the difference because 6AT's are geared differently that 6MT's.

It seems like you talking about 1/4 mile runs, not 0-60, correct? 1/4 mile runs would involve more shifts than just 1st to 2nd, whereas 0-60 only requires 1st to 2nd. I've only addressed 1st to 2nd. It could be that optimal shift points vary for multiple shifts so they picked a number that's less than redline because it works the best across all the shifts.

You mentioned there are issues with revving the 6AT to high RPM. Could that be why they shifted before redline - because they had to?

There's an answer here. It would be nice to find it.

By the way, my analysis is consistent with your "butt dyno" comments. I acknowledge that you can feel the drop off in torque at the high end. But I'm saying that according to the numbers, staying in the lower gearing longer should more than make up for the drop in T.

Last edited by driverman; 01-13-2013 at 12:21 PM.
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      01-13-2013, 01:34 PM   #55
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No problem. The first answer is I have no idea why to magazines shift at red line or if they actually do shift at redline....never really noticed. Can you do a quick cut & paste on one talking about the shift points for the test.

I know a lot of the test data lists the speed in gears at red line but this does not say that’s where they are shifting itd just data about how its geared.

I also know based on some old C&D/R&T article on how they test that they make multiple runs doing all kinds of start & shift techniques & just publish the best runs. This is why 99% of the time stock for stock average Joes cannot equal the performance magazines achieve.

BTW I do agree that some cars might be designed to shift at red line for max performance but what I said is red line is first & foremost the do not exceed this RPM point which may or may not be the optimum shift point.

Most all stock turbo records are 6AT’s because the 6MT in the 135/335 is not all that good at drag racing but very good at track days. You are correct that the number of shifts required will effect the ET. However since gear ratios are the gear ratios your math will work equally well with 6AT, 7DCT & 6MT. Tire size (diameter) will also effect the equation because it effects the final gear ratio if not the same car to car.

Terry's car runs 0-60 in 3.0. Most of the record cars also have VBOX screens posted, these are the same units mags run. The first key to a top time is the 60 foot elapsed time which will be the same for all the cars because the 1/2 shift will come later. The other thing you need to know is that at the 1/8 mile point your car regardless of performance potential is pretty much all done piling on the MPH. Typically an average high performance car will add 22/25mph in the second half while record cars will add about 30mph. Example my car, average Joe, does 90mph at the 1/8 mile timer but only increases to 114mph at the finish.

The AT trans issue occurs in 5th gear so is not relevant in 0-60 at all or typically in the 1/4 mile. IIRC you need to be getting up around 130mph+ for the problem to rise.

Final thing I am not discounting your math I used it myself staring in 1960 as a starting point, where we disagree a bit is whether its an absolute predictor or a good tool to get you into the ball park.
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      01-13-2013, 01:39 PM   #56
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Great response BEAR-AvHistory. Thanks. This is a good dialogue.

I'll try to respond later today. I'm in the middle of something.

I will point out one quick thing. The different gearing in the 6AT could very well have an effect on optimum shift points. I'll run the numbers and post them when I respond.
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      01-13-2013, 06:53 PM   #57
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Just to throw you a small curve since you are redoing the numbers most top running 6AT's start in 2nd gear to maintain traction at launch, 1st tends to overpower the tires. One poster who uses a different style launch is BuraQ 7DCT who uses his 335is launch control which forces a 1st gear start. As far as I know the 6MT's use first gear.

So when you do the numbers you need to run the 6MT with a first gear ratio & the 6AT with a 2nd gear ratio to start.
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      01-13-2013, 08:08 PM   #58
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That's pretty quick, sounds good too.
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      01-13-2013, 10:24 PM   #59
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Quote:
Originally Posted by AdrianRex View Post
Does the filter really make a difference? It's not very expensive, will buy if it really does make a difference.
IMHO no measurable difference others will disagree. I have an 330Ci & don 't see the air filter as being a choke point, no pun intended. I also run a stock system on my 335is & would not bother thinking about the intake system unless I was making a bit over 400whp.
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      01-13-2013, 10:57 PM   #60
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Comparing the variations of the N52, it seems that the manifold is the choke point on the 328 intake, not the filter. If it were harmless, the low cost could justify going for the mod anyway, but the KN being an oiled filter, there is always the risk of ruining the MAF, which is quite coslty.
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      01-19-2013, 11:52 AM   #61
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Hey guys I raced my friends 2010 camaro v6 manual yesterday....I have a 2010 e92 330i xDrive auto, it was imported in may of 2010. Anyways

The camaro has
-injen tuned cold air intake
-CNT racing single outlet exhaust
-tuned

my 330i
-intake mod
electric cut out in place of my resonator only my primary cats are infront of my cut out.

that night it was 29degreees we were at 40 he was in second i was in third and we went and were neck and neck but he pulled slowly so i dropped to second i caught up and we were neck up to 120 but then there was traffic i had one passenger he had 2 each were 140 and the driver him self is 180

our second run was from a dig. i had given him a car length head start bc he was complainig i have awd so i gave it to him. I also had a 120lb passenger and i my self i am 250lbs he had no passengers

my friend who was in my car has a 2010 jetta 2.5 se auto with the DSG transmition he has an intake and a cut out and he also ran it with the camaro nad i was filing i decided to throw that video in

revving --->

jetta ---->

330i ----->
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