[blipblip]

Hi guys,
I just bough a E90 335i and will start tracking it soon (once it is broken in...)

A question though:
Judging from the spec sheet of our car, I think shifting at around 6000RPM rather than winding it out to redline is more efficient, and may even help with cooling. Is this observation correct?

(btw, I am an experienced track driver, albeit with other cars...

[longodj]

Originally Posted by blipblip

Hi guys,
I just bough a E90 335i and will start tracking it soon (once it is broken in...)

A question though:
Judging from the spec sheet of our car, I think shifting at around 6000RPM rather than winding it out to redline is more efficient, and may even help with cooling. Is this observation correct?

(btw, I am an experienced track driver, albeit with other cars...

Yep, that's how I do it. I may even shift a bit earlier as our power starts tapering after 5500 stock and I don't have an O/C yet....soon hopefully!

[blipblip]

Thank you.

Cheers!

[leftcoastman]

Originally Posted by blipblip

Hi guys,
I just bough a E90 335i and will start tracking it soon (once it is broken in...)

A question though:
Judging from the spec sheet of our car, I think shifting at around 6000RPM rather than winding it out to redline is more efficient, and may even help with cooling. Is this observation correct?

(btw, I am an experienced track driver, albeit with other cars...

It isn't as simple as looking at the dyno.

You need to map out the dyno for your specific car and apply gear ratios. What you're trying to determine is the TORQUE TO THE GROUND, which is very dependent on gearing.

The engine torque gets multiplied by both the gearbox and the rear end. In other words, if you're putting out 300lb-ft from the engine and you are in 1st gear, you are putting 300 x 4.06 (1st gear ratio) X 3.08 (rear end ratio) = 3751.44 lb-ft to the ground.

The proper way to calculate the right place to shift is to determine how much torque TO THE GROUND would be achieved by shifting and how much is achieved by staying in the same gear.

In the lower gears (1-2, 2-3), the percentage difference in multiplication is huge (change in gear ratios is large), so it behooves you to shift later. Basically you are balancing the loss in torque at higher engine rpms (note how the torque curve trends down at high rpm) with the loss in gear multiplication from upshifting.

For my 6MT car, I applied my dyno results (Procede) and got the following:

1-> 2 ......6700rpm
2-> 3 ......6500rpm
3-> 4 ......6150rpm
4-> 5.......5850rpm
5-> 6 ......5800rpm

Note that it will change based on your specific engine output, which is dependent on what tune, if any, you have.

But this is a good baseline.

[roy@gambitmotorsport]

Originally Posted by leftcoastman

It isn't as simple as looking at the dyno.

You need to map out the dyno for your specific car and apply gear ratios. What you're trying to determine is the TORQUE TO THE GROUND, which is very dependent on gearing.

The engine torque gets multiplied by both the gearbox and the rear end. In other words, if you're putting out 300lb-ft from the engine and you are in 1st gear, you are putting 300 x 4.06 (1st gear ratio) X 3.08 (rear end ratio) = 3751.44 lb-ft to the ground.

The proper way to calculate the right place to shift is to determine how much torque TO THE GROUND would be achieved by shifting and how much is achieved by staying in the same gear.

In the lower gears (1-2, 2-3), the percentage difference in multiplication is huge (change in gear ratios is large), so it behooves you to shift later. Basically you are balancing the loss in torque at higher engine rpms (note how the torque curve trends down at high rpm) with the loss in gear multiplication from upshifting.

For my 6MT car, I applied my dyno results (Procede) and got the following:

1-> 2 ......6700rpm
2-> 3 ......6500rpm
3-> 4 ......6150rpm
4-> 5.......5850rpm
5-> 6 ......5800rpm

Note that it will change based on your specific engine output, which is dependent on what tune, if any, you have.

But this is a good baseline.

Thank you very, very much for the insight. This was my natural instinct based on the way the pull drops (or doesn't) in different gears. Also, with turbos, I've found taking it up high in the RPM range and shifting quickly seems to transfer more boost into the next gear. For instance, shifting from 2->3 at 5500 RPMs feels nice, but doing so at 6500 RPMs chirps the tires.


Roy

[mistermojorizin]

Originally Posted by leftcoastman

It isn't as simple as looking at the dyno.

You need to map out the dyno for your specific car and apply gear ratios. What you're trying to determine is the TORQUE TO THE GROUND, which is very dependent on gearing.

The engine torque gets multiplied by both the gearbox and the rear end. In other words, if you're putting out 300lb-ft from the engine and you are in 1st gear, you are putting 300 x 4.06 (1st gear ratio) X 3.08 (rear end ratio) = 3751.44 lb-ft to the ground.

The proper way to calculate the right place to shift is to determine how much torque TO THE GROUND would be achieved by shifting and how much is achieved by staying in the same gear.

In the lower gears (1-2, 2-3), the percentage difference in multiplication is huge (change in gear ratios is large), so it behooves you to shift later. Basically you are balancing the loss in torque at higher engine rpms (note how the torque curve trends down at high rpm) with the loss in gear multiplication from upshifting.

For my 6MT car, I applied my dyno results (Procede) and got the following:

1-> 2 ......6700rpm
2-> 3 ......6500rpm
3-> 4 ......6150rpm
4-> 5.......5850rpm
5-> 6 ......5800rpm

Note that it will change based on your specific engine output, which is dependent on what tune, if any, you have.

But this is a good baseline.

thanks for this.

there's two equations you can apply and they both give the same results.

1) you can find the gear 1 rpm where: torque, multiplied by the gear ratio of gear 1, in gear 1 = the torque, multiplied by the gear ratio of gear 2, if shifted to gear 2

or

2) you can find the rpm where: the power in gear 1 = the power in gear 2, if shifted to gear 2

either one will produce the same results.

if you search this forum, you will find that someone has already done the math for a stock 335.

gear shift rpm
gear 1 - redline
gear 2 - redline
gear 3 - 6700
gear 4 - 6400
gear 5 - 6400

[mistermojorizin]

Originally Posted by roy@gambitmotorsport

Thank you very, very much for the insight. This was my natural instinct based on the way the pull drops (or doesn't) in different gears. Also, with turbos, I've found taking it up high in the RPM range and shifting quickly seems to transfer more boost into the next gear. For instance, shifting from 2->3 at 5500 RPMs feels nice, but doing so at 6500 RPMs chirps the tires.


Roy

that chriping effect happens on all cars, not just turbos, if you shift where it drops you near the torque peak in the next gear. not sure if shirping makes it accelerate faster tho

[roy@gambitmotorsport]

Originally Posted by mistermojorizin

that chriping effect happens on all cars, not just turbos, if you shift where it drops you near the torque peak in the next gear. not sure if shirping makes it accelerate faster tho

Agreed on the possibly "not"-faster part; but it's always fun doing it from 2nd->3rd when passing motorcycles up the crest.

I do think the turbos have a little to do with it, though - at least, on a modified set-up. Just put in the clutch and let the accelerator go at different RPMs and hear the difference in the spool-down.


Roy