[ChubbsBmth]

Seen some discussions on this and think I remember that the N54 engine its best to change gear around to 6000rpm instead of 7000k, is this true?

Sure one of the more educated members will know if this is correct and the reasons why?

I am trying to learn more about cars and the finer details so dont shoot me down if this seems stupid and it should be nearer to redline...

Cheers

[doughboy]

The standard 335i hits a wall and runs out of puff above about 5800rpm, so 6k is about best to drop you back into the torque at about 4.5-5k in the next gear. I'll try and find a dyno curve to illustrate.

The red line isn't really showing you the most power or the best point to shift, it's just saying 'engine may explode above this point'

TBH you can rarely get it that high anyway I find, first needs a short shift to prevent traction / wheelspin, then maybe second gear is your only chance to wring it out as 3rd will be doing 100mph by 7K and that's illegal as we all know.

[DavS1]

Wherever they make peak power! there's really no point in revving it any higher if you're wanting to go quick

[Kerr]

Originally Posted by DavS1

Wherever they make peak power! there's really no point in revving it any higher if you're wanting to go quick

I'd like to see Doughboy's dyno results.

It might be beneficial to rev to 6300rpm and have 280bhp than change gear and drop to 270bhp at 4800rpm.

Purely guess figures but you get the idea.

[dxb335d]

Dav's right deffo.


Mine makes peak power at 8k sha moan!!


Dough mate, it wont blow up. It has a limiter.

[zltm089]

6k rpm is about right....not much power after that....for the n54

[benzy89]

~6200 RPMs -- Look at a dyno sheet (or if you can, dyno your car to get the best results) and look for where your powerband starts to dip


Anything above 6,500 RPMs is just for noise

[DavS1]

Originally Posted by Kerr

I'd like to see Doughboy's dyno results.

It might be beneficial to rev to 6300rpm and have 280bhp than change gear and drop to 270bhp at 4800rpm.

Purely guess figures but you get the idea.

Yea I see what your saying, but if you revved past peak power, shifted and dropped to just bellow, or on peak power, you'll be out of the power band quicker than you would be if you shifted on peak power if you see what I mean?

[dxb335d]

Don't forget it's got loads of torque!!

[DavS1]

is peak torque not at like 4-4500?

[m1bjr]

5k5

[doughboy]

Originally Posted by dxb335d

Dough mate, it wont blow up. It has a limiter.

I know mate, I was just saying the redline isn't a shift indicator as perhaps some may think.

My diesel van has a redline at 5k, but it won't rev past 4 even in neutral.


The standard N54 makes max torque at about 2krpm then it plateaus (limited by ECU) to about 5k then falls away.

Tuned its more peaky, peak at 2k then falls away from there. See my dynos attached, but peak power (tuned) is still only just past 6k. (JB3, map 6, DPs and DCI)

Agree with m1jbr, on the road, short shifting by 5.5k makes for faster progress with less noise, ride the torque a little.

[craneboy]

Originally Posted by doughboy

My diesel van has a redline at 5k, but it won't rev past 4 even in neutral.

That's more to do with the speed in which diesel burns at.
In theory the engine could rev well beyond, but the diesel burn speed limits the engine revs.

HTH

Andy

[doughboy]

Originally Posted by craneboy

That's more to do with the speed in which diesel burns at.
In theory the engine could rev well beyond, but the diesel burn speed limits the engine revs.

HTH

Andy

Yes understood, but my point was about the incorrectness of red lines on tacho's, they're not necessarily related to the driving characteristic of the engine (thus not a shift marker), just a maximum mechanical rev marker.

In the case of a diesel, you could exceed this by buzzing the engine on an overly agressive downshift.

[m1bjr]

My point about making a shift at 5,500rpm is reaction time.

If you anticipate a 5k5 shift, in low ranges you will certainly be making 6k maybe more before lifting

[Guvernator]

Originally Posted by m1bjr

My point about making a shift at 5,500rpm is reaction time.

If you anticipate a 5k5 shift, in low ranges you will certainly be making 6k maybe more before lifting

Yep, if I am driving the car in manual mode, I usually pull the change up paddle at around 5krpm as by the time my brain has registered it and told my finger to pull the paddle, it's already zinged round to 6k, especially in first and second gear.

This does raise an interesting point though. I always assumed the best way to get maximum acceleration was to hold onto the gear and change right on the limiter but if peak power and torque arrive way before the limiter then some are suggesting that it's better to shift up earlier.

If that is the case though, why if you leave the car in auto\sport mode does it not change up earlier? Surely it should be programmed to change at the optimum change point of 5.5k but it takes it all the way to the limiter.

[shrink]

the thing to watch out for is that you're allowing it to rev high enough, that when you change gear, you don't drop below the power band of the engine.

So changing at 5k for it to drop down to say 3.5k may mean the engine lags a little and you lose power in the change. If you were to hang on to 5.5k for example, you might end up shifting up and being at about 4k, meaning you're on the power and good to go. So sometimes sticking in gear a little longer can have benefits for the amount of available power in the next gear. It's not always about shifting at the cars maximum power point.

[zltm089]

Originally Posted by shrink

the thing to watch out for is that you're allowing it to rev high enough, that when you change gear, you don't drop below the power band of the engine.

So changing at 5k for it to drop down to say 3.5k may mean the engine lags a little and you lose power in the change. If you were to hang on to 5.5k for example, you might end up shifting up and being at about 4k, meaning you're on the power and good to go. So sometimes sticking in gear a little longer can have benefits for the amount of available power in the next gear. It's not always about shifting at the cars maximum power point.

even at 3.5k...you'd still be in the "power" range....mid range power on the n54 engine is very very good....even at 2k rpm...i always feel like a "lil kick" with the torque!....

[Guvernator]

I suspect the turbo setup in a 335i does confuse the issue somewhat as it makes quite a significant amount of power\torque fairly early whereas in something like an M3, there is a lot more merit in wringing it out, besides just the awesome noise of course.

[F104]

You want to shift when the next gear gives better acceleration. To figure that out you need to take the torque curve and use that to determine tractive effort at the wheels in each gear, after rolling restistance, air flow resistance and then see what force is left to accelerate the mass of the car. If you plot that you get this graph (for my evolved 320D). You want to shift at each intersection. The graph doens't show rpm, but my spreadsheet show these as optimum.

1st->2nd: 4612rpm
2nd->3rd: 4459 rpm
3rd->4th: 4326rpm
4th->5th: 4179 rpm
5th->6th: 4129 rpm
Note that were you shift in the higher gears there is no obvious break point to let you feel were to shift.

Question is off course if this model is any good. It shows my car will stop accelerating at at 249 kph if the (level) road was long enough. It has seen 250kph indicated a few times, should be about 240 real, and i believe it could do a bit more more given more road. Good enough for me.

[F104]

the graph

[benzy89]

Originally Posted by Guvernator

If that is the case though, why if you leave the car in auto\sport mode does it not change up earlier? Surely it should be programmed to change at the optimum change point of 5.5k but it takes it all the way to the limiter.

If you put the car in DS & don't touch the paddles or click-up/down on the gear stick, then it'll auto shift for you depending on throttle modulation (the DS letters will remain on the info display). The minute you touch the paddles/gear shift knob, you're responsible for shifting & the computers doesn't get involved until downshifts (sub 2k downshifts only). Once you're in control, it'll let you ride a gear straight into redline (unnecessary abuse on the engine).

Low 6k is the optimal shift points, above 6,500 RPMs the turbos are out of their efficency range & you're doing more damage than anything else

Originally Posted by Guvernator

I suspect the turbo setup in a 335i does confuse the issue somewhat as it makes quite a significant amount of power\torque fairly early whereas in something like an M3, there is a lot more merit in wringing it out, besides just the awesome noise of course.

The S65's peak HP is up really high, design of the motor