Acceleration Mods - What to expect?

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just-right
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Acceleration Mods - What to expect?

Post by just-right » Sun Jul 12, 2020 12:02 pm

I have been looking at a few performance mods for the M. I have wondered what kind of change could be expected in acceleration time. Considering last week’s bad weather I had some time to write a little program that simulates a Z4M in acceleration all the way up to top speed. I thought some of you might be interested in the results.

In OEM spec the figures are not too far off real life data (). They would be pretty close accounting for shifting:
0 – 100 kph : 4.91s (4.9 – 5.0)
0 – 200 kph : 16.73s (17.0)
400 m : 13.06s (13.2)
1000 m : 23.51s
Vmax : 281.1 kph
Max g : 0.63

First look is at different final drive ratios, comparing the stock 3.62 (Blue) to 3.91 (Red) and 4.1 (Green). A shorter final drive is a bit quicker across the board and helps top speed as well by being closer to max power.
0 – 100 kph : 4.91s -> 4.82s -> 4.81s
0 – 200 kph : 16.73s -> 16.46s -> 16.34s
Vmax : 281.1 kph -> 284.5 -> 285.4 redlining 6th gear
Tyre_FX_Final_Drive.png
Tyre_FX_Final_Drive.png (35.12 KiB) Viewed 1883 times
First gear acceleration is similar to stock as you are grip limited (dotted line). Acceleration after that is slightly better for the shorter final drive ratios when you are in the same gear and drops off where the gears are offset (i.e. 3rd gear on 4.1 and 2nd on 3.62 ratio). The time delta and the delta of longitudinal tyre force shows this behaviour and their relationship quite well.
Time_Delta_Final_Drive.png
Time_Delta_Final_Drive.png (37.79 KiB) Viewed 1883 times
Tyre_FX_Delta_Final_Drive.png
Tyre_FX_Delta_Final_Drive.png (36.2 KiB) Viewed 1883 times
The original gear and final drive ratios would theoretically allow a top speed of over 300 kph. The OEM 6th gear and final drive combination is mainly chosen to keep the cruising RPM and fuel consumption a bit lower. The RPM drop is defined by the gearbox ratios and therefore do not change.
RPM_Final_drive.png
RPM_Final_drive.png (46.3 KiB) Viewed 1883 times
Overall, shortening the final drive looks like a pretty solid step. I will have a look at some other options, like increased power and weight reduction.
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Jembo
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Acceleration Mods - What to expect?

Post by Jembo » Sun Jul 12, 2020 12:30 pm

IMO the only real S54 choice for a noticeable S54 acceleration upgrade is Nos or a Supercharger, though not for me.

Otherwise a cheaper(ish) alternative to slightly changing the drive ratios is also to use 19” rims with 30 profile 265x19 tyres, as the rolling circumference is smaller than 255x35x19 or the standard 255x40x18
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Acceleration Mods - What to expect?

Post by Smartbear » Sun Jul 12, 2020 12:41 pm

Jembo wrote: Sun Jul 12, 2020 12:30 pm IMO the only real S54 choice for a noticeable S54 acceleration upgrade is Nos or a Supercharger, though not for me.

Otherwise a cheaper(ish) alternative to slightly changing the drive ratios is also to use 19” rims with 30 profile 265x19 tyres, as the rolling circumference is smaller than 255x35x19 or the standard 255x40x18
Going to 19”s might not help so much as the wheels are generally heavier than 18”s and can slow acceleration because of this :?
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Acceleration Mods - What to expect?

Post by Jembo » Sun Jul 12, 2020 2:00 pm

Smartbear wrote: Sun Jul 12, 2020 12:41 pm
Jembo wrote: Sun Jul 12, 2020 12:30 pm IMO the only real S54 choice for a noticeable S54 acceleration upgrade is Nos or a Supercharger, though not for me.

Otherwise a cheaper(ish) alternative to slightly changing the drive ratios is also to use 19” rims with 30 profile 265x19 tyres, as the rolling circumference is smaller than 255x35x19 or the standard 255x40x18
Going to 19”s might not help so much as the wheels are generally heavier than 18”s and can slow acceleration because of this :?
Rob
I’d normally agreed with this had I not found the 19” CSL’s i put on are lighter than the OEM 224 18”
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Acceleration Mods - What to expect?

Post by brillomaster » Sun Jul 12, 2020 4:15 pm

Grip limited in first gear? Sticky tyres will sort that. Though your drivetrain wont last as long. And less weight will definitely help, simple force = mass x acceleration.

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Acceleration Mods - What to expect?

Post by buzyg » Sun Jul 12, 2020 6:26 pm

Weight is the key. Z4M is a bit of lard a#se. :o Start with a Caterham and modify that. :wink:
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Acceleration Mods - What to expect?

Post by Argenta » Mon Jul 13, 2020 3:26 pm

Shorter gearing? I’d like it longer if anything! 😊

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Acceleration Mods - What to expect?

Post by R_P_M_ » Mon Jul 13, 2020 4:42 pm

I think on the road it'll make a massive difference as most of the time you're in 3rd on a nice b road, and the top of 3rd is very illegal as standard.
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Acceleration Mods - What to expect?

Post by Felix79 » Thu Jul 16, 2020 3:45 pm

buzyg wrote: Sun Jul 12, 2020 6:26 pm Weight is the key. Z4M is a bit of lard a#se. :o Start with a Caterham and modify that. :wink:
Best weight reduction I've done with my M is lose 3 stones myself :rofl:

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Acceleration Mods - What to expect?

Post by wonkydonkey » Fri Jul 17, 2020 4:57 pm

Argenta wrote: Mon Jul 13, 2020 3:26 pmI’d like it longer if anything! 😊
Wouldn't we all? :? :lol:
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Acceleration Mods - What to expect?

Post by Argenta » Sun Jul 19, 2020 7:25 pm

Ha!

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Acceleration Mods - What to expect?

Post by just-right » Mon Jul 20, 2020 10:30 pm

You walked straight into that one Argenta! :lol: I think slightly shorter gearing, especially in 3rd gear could be quite nice on some winding B-roads. The time from 100 to 150 kph is not far of 5% quicker.

Damn that old Newton dude: more power less weight, simples. :thumbsup: I had a quick look at some weight sensitivities, removing 20 kg (Red) and 20 kg from the rotational assembly (Green)

0 – 100 kph : 4.91s -> 4.87s -> 4.86s
0 – 200 kph : 16.73s -> 16.54s -> 16.48s

The acceleration time deltas are not ground breaking, as will be the case with a lot of the parameters in relatively small quantities. Now if we were to remove 200 kg (Red) you can expect a decent improvement.

0 – 100 kph : 4.91s -> 4.59s
0 – 200 kph : 16.73s -> 14.86s

Obviously around a race track a 20 kg weight reduction in braking and cornering in addition to the acceleration benefits will easily yield a few tenths a lap.
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Acceleration Mods - What to expect?

Post by just-right » Fri Aug 28, 2020 11:16 am

Adding some good old power this time in the form of a uniform 20Nm increase (Red) at any rpm and the fitment of a ESS VT2-525 supercharger (Green) The 20 Nm increase results in about 22 hp at peak rpm.

0 – 100 kph : 4.91s -> 4.79s -> 4.46s
0 – 200 kph : 16.73s -> 15.76s -> 12.24s

Hitting 525 crank HP is not too bad 8) You should theoretically be able to hit the rev limiter in 6th gear as well.
Long_G_Power.png
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Acceleration Mods - What to expect?

Post by mmm-five » Fri Aug 28, 2020 1:53 pm

just-right wrote: Fri Aug 28, 2020 11:16 am Hitting 525 crank HP is not too bad 8) You should theoretically be able to hit the rev limiter in 6th gear as well.
Only if we assume you also remove the software-controlled 6th gear speed limiter, otherwise more power will simply get you to that limiter faster - and your VMAX will still be in 5th gear :P
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Acceleration Mods - What to expect?

Post by beanie » Fri Aug 28, 2020 4:57 pm

I think the standard gearing is pretty well judged and looking at the data, it seems I’d be far better off telling the girlfriend to catch the bus and saving her weight and luggage. :lol:
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