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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 03-18-2005, 11:29 AM
Will_325i Will_325i is offline
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At what RPM should I shift for max accel?

I'll be honest, I'm asking mostly just for curiosity. I usually just "feel" when it's the right moment to shift. At any rate, I find that often this "point" is very close to the rev-limiter.

I assume each gear should have a slightly different optimum rpm to upshift.

Thoughts?
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  #2  
Old 03-18-2005, 11:39 AM
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BlackChrome BlackChrome is offline
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I'd say right before the fuel cutoff (so, um, 6500RPM).

IMHO, the reason why so high, is because when you shift to the enxt gear, the RPM won't drop too low (when compare to, say, 5500RPM).

Please correct me if I am wrong.
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  #3  
Old 03-18-2005, 11:50 AM
Will_325i Will_325i is offline
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Quote:
Originally Posted by BlackChrome
I'd say right before the fuel cutoff (so, um, 6500RPM).

IMHO, the reason why so high, is because when you shift to the enxt gear, the RPM won't drop too low (when compare to, say, 5500RPM).

Please correct me if I am wrong.
I totally agree, but then the problem becomes statistical.......how many times out of a hundred can you shift within 100 rpm of the limiter without actually reaching the limiter?

I would guess, though, that if two gears are very close in ratio that it may not be necessary to go so high in rpm.
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  #4  
Old 03-18-2005, 11:52 AM
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Nick325xiT 5spd Nick325xiT 5spd is offline
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In a BMW, the limiter.

But generally speaking, it depends on the torque curve.
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  #5  
Old 03-18-2005, 01:24 PM
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Quote:
Originally Posted by rumratt
What he said.

They only way you would shift earlier than redline is if your torque drops of quite a lot at higher rpms. The increase in torque gained from shifting (by moving back to the torque sweet spot) would need to outweight the gearing disadvantage of the higher gear. With a realtively flat torque curve, this ain't gonna happen, particularly for the lower gears where the difference between gears is huge.
I'll third that- what you should do is search for a dyno chart of someone's car that has the same engine as yours, and see where your power drops off. That'll show a visual of what you're looking for.

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  #6  
Old 03-18-2005, 02:38 PM
TeeKay TeeKay is offline
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Look at the flasing lights...

The flashing light on the tach should flash madly to indicate when the optimal shifting point should be. It's pretty neat. It was on the M3 I test-drove. I don't remember it being on an Auto 325. What about the other manual 3-series, do they have this feature?
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  #7  
Old 03-18-2005, 08:16 PM
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Quote:
Originally Posted by rumratt
What he said.

They only way you would shift earlier than redline is if your torque drops of quite a lot at higher rpms. The increase in torque gained from shifting (by moving back to the torque sweet spot) would need to outweight the gearing disadvantage of the higher gear. With a realtively flat torque curve, this ain't gonna happen, particularly for the lower gears where the difference between gears is huge.
Actually, torque dropping off isn't really the issue as much as horsepower dropping off. When you shift into the next gear, the engine may make more torque, but it has less gear multipication. You want to shift when the horsepower in the current gear is less then horsepower in the next gear. However, in most modern cars (BMW's included), that point is beyond the manufacturer-imposed redline, so shift at redline. Of course, there are examples against this, but most are large domestic V-8's that aren't optimized for high rpm breathing.
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  #8  
Old 03-18-2005, 08:29 PM
Will_325i Will_325i is offline
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Quote:
Originally Posted by cwsqbm
...

However, in most modern cars (BMW's included), that point is beyond the manufacturer-imposed redline, so shift at redline. ....
Is that because of a flat torque curve AND big gear ratio differences? I mean in a CVT the car should never reach redline. Right?
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  #9  
Old 03-18-2005, 08:38 PM
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Quote:
Originally Posted by TeeKay
The flashing light on the tach should flash madly to indicate when the optimal shifting point should be. It's pretty neat. It was on the M3 I test-drove. I don't remember it being on an Auto 325. What about the other manual 3-series, do they have this feature?
No.
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  #10  
Old 03-18-2005, 08:42 PM
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it's not even on all M3's
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  #11  
Old 03-19-2005, 01:41 AM
Alex Baumann Alex Baumann is offline
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Objection to the shifting light idea ! This is not a race car.

I don't understand the trend to make the 3 Series car into a race car. It is not and it was not meant to be a race car
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  #12  
Old 03-19-2005, 01:49 AM
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Quote:
Originally Posted by TeeKay
The flashing light on the tach should flash madly to indicate when the optimal shifting point should be. It's pretty neat. It was on the M3 I test-drove. I don't remember it being on an Auto 325. What about the other manual 3-series, do they have this feature?
Some of us have been adding a shift-up warning to our E36s. I think it is neat and keeps me from hitting the rev limiter when I overtake. It also once saved me from an over-rev while I was still developing it. Arguably, that only happened because I was developing it. Still, it may easily pay for itself some day.
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  #13  
Old 03-19-2005, 06:06 AM
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6500 rpms which is redline in my car. I usually shift just a little before so I don't break anything.
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  #14  
Old 03-19-2005, 09:16 AM
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Quote:
Originally Posted by TeeKay
The flashing light on the tach should flash madly to indicate when the optimal shifting point should be. It's pretty neat. It was on the M3 I test-drove. I don't remember it being on an Auto 325. What about the other manual 3-series, do they have this feature?
The only flashing light I see is behind me!
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  #15  
Old 03-19-2005, 03:00 PM
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Artslinger Artslinger is offline
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I like to shift between 4000 - 4500 rpms.
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  #16  
Old 03-19-2005, 03:34 PM
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Nick325xiT 5spd Nick325xiT 5spd is offline
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Quote:
Originally Posted by Alex Baumann
Objection to the shifting light idea ! This is not a race car.

I don't understand the trend to make the 3 Series car into a race car. It is not and it was not meant to be a race car
I'm turning one into a race car.
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  #17  
Old 03-19-2005, 04:06 PM
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cwsqbm cwsqbm is offline
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Quote:
Originally Posted by Alex Baumann
Objection to the shifting light idea ! This is not a race car.

I don't understand the trend to make the 3 Series car into a race car. It is not and it was not meant to be a race car
If we don't occasionally "race" our cars, why don't we all drive 318i's instead of all the 325i's and 330i's in the U.S.?

Its not the ideal race car, but for some, our cars need to be multipurpose. So my 330 will see a little driving school, a little autox, and an occasional blast down the interstate. I'd love a separate car for each, but I've already run of out of parking.

Also, the shift light is a good idea because I don't shift at redline on most drives, so I'm not tuned to it like I was on old, slower cars that required aggression just to keep up with traffic. Plus, its so smooth compared to other cars I drive (nothing like a Chevy Classic to make coming home to a BMW feel so good.)
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  #18  
Old 03-19-2005, 08:55 PM
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Quote:
Originally Posted by Artslinger
I like to shift between 4000 - 4500 rpms.
I'll bet you can't wait till she's broken in, huh?

Since you stand to gain/lose thousandths of seconds by the exact right shift point, I would suggest investing in multiple runs at the track where you are performing these race maneuvers. You aren't doing this on the street, are you? I mean, on the street you *shouldn't* be racing, especially past the posted speed limit (which means one shift, 1st to 2nd in pretty much every instance), and the difference in the shift point will mean the difference of almost nothing.

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  #19  
Old 03-20-2005, 10:12 AM
Orient330Ci Orient330Ci is offline
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The 3-series are great performers, and I know, BMW's are meant to be driven.

But do you guys push your cars this hard all the time? If you're pushing close to redline all the time then you're hauling ass way over local speed limits. No?

Were all these posts talking about track time? Or am I just not driving fast enough?
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  #20  
Old 03-20-2005, 12:10 PM
Alex Baumann Alex Baumann is offline
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Quote:
Originally Posted by cwsqbm
If we don't occasionally "race" our cars, why don't we all drive 318i's instead of all the 325i's and 330i's in the U.S.?

Its not the ideal race car, but for some, our cars need to be multipurpose. So my 330 will see a little driving school, a little autox, and an occasional blast down the interstate. I'd love a separate car for each, but I've already run of out of parking.

Also, the shift light is a good idea because I don't shift at redline on most drives, so I'm not tuned to it like I was on old, slower cars that required aggression just to keep up with traffic. Plus, its so smooth compared to other cars I drive (nothing like a Chevy Classic to make coming home to a BMW feel so good.)
[Alex Mode On]

I race on the Autobahn, I race it as much as possible. I'm a devil on the unrestricted sections, but I never felt the need for a shift light. I just shift by feel. I know when it's time to shift.

[Alex Mode Off]

PS : What makes you think that you can't race a 318i ? I saw a lot of underpowered cars upsetting horsepower monsters on the track.
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  #21  
Old 03-20-2005, 12:11 PM
Alex Baumann Alex Baumann is offline
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Quote:
Originally Posted by Nick325xiT 5spd
I'm turning one into a race car.
That's the key word
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  #22  
Old 03-20-2005, 01:43 PM
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Quote:
Originally Posted by RSPDiver
I mean, on the street you *shouldn't* be racing, especially past the posted speed limit (which means one shift, 1st to 2nd in pretty much every instance)
Onramps.

Some onramps have high visibility where you can see traffic flow. You can push hard and get into 3rd aggressively and still shut it down around 75 before you merge (or get spotted by a cruising cop).
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  #23  
Old 03-21-2005, 08:48 AM
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Quote:
Originally Posted by Alex Baumann
What makes you think that you can't race a 318i ? I saw a lot of underpowered cars upsetting horsepower monsters on the track.
Exactly!! Every 1 mph gain in exit speed is a 1 1/2-ft gain over every second of acceleration on the straight. If you can manage exit speed of, say, 5 mph faster than that HP monster, not only are you gaining in the turn but you will be gaining 7 1/2 ft for every second of acceleration on the straitway. Sure, their HP will kick in on the straigtway but first they have to catch up to that 5 mph difference AND then reach a higher speed than the 318 AND carry that high speed for a bit to offset the time the HP monster already lost. On tighter tracks, a 318 can do pretty well. On track with long straightway long Road America, though, top end would be a huge disadvantage.
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