Forum's Z4s top speed listing

[B21]

Following on from various noodles here is a database of production Z4s of all versions ..the idea is to add Forum members modded ones to it as well.

Asome folks asked for a list of what standard models would do ranked against each other.

I've sorted it into two versions a manufacturer only version (sorted by version the engine size) and one with all comers (sorted on speed).

To state the obvious its a bit of fun, if you can't take it on that basis go somewhere else.

Most cars will hit other issues like instabiliy, tyre ratings, heat soak, power fade etc..assumes derestricted and best gear combo etc

Speed is based on an iteration of several models which seems pretty close, as usual raises some questions.

There's a database you can look at with all the calculatons here.. https://www.dropbox.com/s/7jzxa5rkssare0l/Z4%20top%20speed%20database.pdf?dl=0

If you do have a modded one we would like to add it..ideally model, new BHP (at crank or wheels), torque, any mods that affect the gearing and ideally a dyno print out or a link to a comparable engine.

Feel free to add to the debate..enjoy

 

[B21]

19/2/2022 edited E85/E86 speeds from query raised, added modified cars and created two tables by alphabetic and by speed

19/2/2022 reversed debate on E85/E86 based on infinite long road argument, corrected pondrew and couple of others..

 

[Pondrew]

OK. Here's my mapped 18i dyno printout:#
Can it break the sound barrier now? :!:

 

[buzyg]

I know it's only a bit of fun.

I have to point out gearing limitations though. The MR and MC will both pull to the limiter in 5th, but 6th is overdrive unless you add forced induction. 172ish is as fast as they can go. I'm ignoring over inflated or larger tyres too, as not standard. :driving:

Maybe with a massive tail wind you could get 6th to work, but that's not really cricket is it.

 

[B21]

I know it's only a bit of fun.

I have to point out gearing limitations though. The MR and MC will both pull to the limiter in 5th, but 6th is overdrive unless you add forced induction. 172ish is as fast as they can go. I'm ignoring over inflated or larger tyres too, as not standard. :driving:

Maybe with a massive tail wind you could get 6th to work, but that's not really cricket is it.

It’s a good point…I cut them a bit of slack by allowing them to rev slightly into the red…after all this is what our primary real world test pilot confirmed..if the jury decides to restrict it to max allowable rpm I can adjust…again how well a car can pull an overdrive gear is a mixture of a dyno / torque chart and folks real workd experience.

The issue as you will see if you look at the calculations table is that all the later cars have increasingly tall gears primarily for fuel economy reasons..often on the 8 speed boxes you are into 5th or 6th as the most appropriate gear for a top speed run.

 

[B21]

OK. Here's my mapped 18i dyno printout:#
Can it break the sound barrier now? :!:
E89Z418i.jpg

Er no..put I will put you in the ‘hall of fame’ :driving:

 

[sars]

A couple of things, [ref]B21[/ref], I know you’ve estimated some losses from crank to wheel, did you take BMW efficient dynamics into account, that is there’s potentially very little losses, those from transmission and diff (going to be less than a kW), as everything else runs off the battery, which only charges when you’re decelerating.

[ref]buzyg[/ref], Physics, the power available at the crank or wheels, is the only thing the governs maximum velocity as long as the final drive gearing and maximum engine rpm allows, gear ratios and thus torque at the wheels governs the time it takes to get to V-max.

 

[B21]

A couple of things, [ref]B21[/ref], I know you’ve estimated some losses from crank to wheel, did you take BMW efficient dynamics into account, that is there’s potentially very little losses, those from transmission and diff (going to be less than a kW), as everything else runs off the battery, which only charges when you’re decelerating.

[ref]buzyg[/ref], Physics, the power available at the crank or wheels, is the only thing the governs maximum velocity as long as the final drive gearing and maximum engine rpm allows, gear ratios and thus torque at the wheels governs the time it takes to get to V-max.

Hi sars, all good points…as usual :rofl:

My first iterations took ‘book’ suggestions for BHP-WHP losses..I then found some dyno runs for N54s where they had done both BHP and WHP iterations which showed that I’d for the N54 over egged the transmission losses so I’ve noodled these back pro-rata..I’ve noodled ( on top of my other noodles) factors for the auto boxes taking into account that there will be some minor incremental losses.

So the WHP numbers take the alternator coasting and air con ditto as far as I can tell…

It’s interesting and I guess not really surprising that as you go faster the absolute amount of power is really all that matters…if these cars were running in a vacuum on the earth they could do 170 mph on about 20 hp…

The numbers seem to be pretty close and consistent…if we get a bit more dyno runs on M40 ZF8HP that would help as it would for the E85s..

In the database I’ve got a column for excess wheel horsepower at the limit..some cars (most) will just run out of power..but some where the gearing falls inappropriately could hit a rev limiter before running out of power..Beedubs supercharged E85M springs to mind..

 

[Smartbear]

I’m surprised that Pondrews 18i only betters the 28i speed by 2mph despite holding an advantage close to 40bhp? :?
Surely it should be faster than that?
Rob

 

[B21]

I’m surprised that Pondrews 18i only betters the 28i speed by 2mph despite holding an advantage close to 40bhp? :?
Surely it should be faster than that?
Rob

Its a manual, max speed in 5th is 160mph and 191 mph in 6th I don't think at 160 mph on the shift it would go down to 250bhp..ish..I'm not sure it would climb out of the hole..its an example off it was going a bit downhill or with a tailwind it could just get enough to climb up..to 166 mph ish?

 

[john-e89]

I don't have a Dyno sheet but my 35is is chipped to 365bhp.

Also my manual 35i is chipped to a supposed 365bhp but feels quicker and pulls harder than the 35is but who knows... :?

 

[sars]

I’m surprised that Pondrews 18i only betters the 28i speed by 2mph despite holding an advantage close to 40bhp? :?
Surely it should be faster than that?
Rob

Its a manual, max speed in 5th is 160mph and 191 mph in 6th I don't think at 160 mph on the shift it would go down to 250bhp..ish..I'm not sure it would climb out of the hole..its an example off it was going a bit downhill or with a tailwind it could just get enough to climb up..to 166 mph ish?

There's a flaw in your thinking, once you change up, yes power will drop, because rpm drops, that's obvious. However, torque causes you to accelerate again, this is an indisputable fact of physics, Newton's second law, published 1687, F = m.a, yes you may well accelerate slowly, but you will accelerate non the less, because there is always a force pushing you. As you accelerate RPM builds and thus power does to. You keep over thinking it, you could be in sixth at 50 mph and as long as you've got distance you'll hit that v-max. As stated previously things that determine actual v-max is power, gearing, drag, frontal area and distance, that's it. Edit: unless you have a speed limiter of course :headbang:

 

[axelleveau]

There's a flaw in your thinking, once you change up, yes power will drop, because rpm drops, that's obvious. However, torque causes you to accelerate again, this is an indisputable fact of physics, Newton's second law, published 1687, F = m.a, yes you may well accelerate slowly, but you will accelerate non the less, because there is always a force pushing you. As you accelerate RPM builds and thus power does to. You keep over thinking it, you could be in sixth at 50 mph and as long as you've got distance you'll hit that v-max. As stated previously things that determine actual v-max is power, gearing, drag, frontal area and distance, that's it. Edit: unless you have a speed limiter of course :headbang:

I am sorry but I have to disagree... As you shift your engine torque will go up but the torque at the wheels will go down as the gearing has changed... As long as power in 6th at the RPM you'll end up at after the shift is lower than power in 5th at the RPM you were before the shift you'll end up slowing down :roll:

 

[Pondrew]

I’m surprised that Pondrews 18i only betters the 28i speed by 2mph despite holding an advantage close to 40bhp?
Surely it should be faster than that?
Rob

Especially as I'm built like a 'racing snake' so would have a major weight advantage over most of you portly folks! :lol: oke:

 

[B21]

I’m surprised that Pondrews 18i only betters the 28i speed by 2mph despite holding an advantage close to 40bhp? :?
Surely it should be faster than that?
Rob

Its a manual, max speed in 5th is 160mph and 191 mph in 6th I don't think at 160 mph on the shift it would go down to 250bhp..ish..I'm not sure it would climb out of the hole..its an example off it was going a bit downhill or with a tailwind it could just get enough to climb up..to 166 mph ish?

There's a flaw in your thinking, once you change up, yes power will drop, because rpm drops, that's obvious. However, torque causes you to accelerate again, this is an indisputable fact of physics, Newton's second law, published 1687, F = m.a, yes you may well accelerate slowly, but you will accelerate non the less, because there is always a force pushing you. As you accelerate RPM builds and thus power does to. You keep over thinking it, you could be in sixth at 50 mph and as long as you've got distance you'll hit that v-max. As stated previously things that determine actual v-max is power, gearing, drag, frontal area and distance, that's it. Edit: unless you have a speed limiter of course :headbang:

sars all noted…the issue which has to be hand calculated that at the higher speeds the power required is going up in a greater than linear fashion but the power tends to rise on a relatively linear line…so in the case of the shift from say 5th to 6th do you drop into a region where the power produced at the reduced rpm is less than the power required for overcoming the drag and rolling resistance..

I made the assumption on pondrew’s car that the jump from 5th to 6th would reduce the rpm by ‘too much’ ..in fact on examination the drop in rpm and hence power available wasn’t as bad as I thought ..

I’ll look at some of the others in due course

Thnx

 

[Pondrew]

made the assumption on pondrew’s car that the jump from 5th to 6th would reduce the rpm by ‘too much’ ..in fact on examination the drop in rpm and hence power available wasn’t as bad as I thought ..

As I thought......I have the fastest E89 in the world (bang per £). Almost a shame that it's been sat in a nice dry garage going nowhere for the last 5 months.

 

[B21]

I’m surprised that Pondrews 18i only betters the 28i speed by 2mph despite holding an advantage close to 40bhp?
Surely it should be faster than that?
Rob

Especially as I'm built like a 'racing snake' so would have a major weight advantage over most of you portly folks! :lol: oke:

so......

Taking sars / smart bear input and 'racing snake' we have a top speed of..drum roll.... 165.0 mph....

If moi and the alledged telly tubby smart bear ( on an enriched beer based diet) were in the same car, at the same time, then the top speed would have been 164.5 mph...result!

 

[Pondrew]

OK so (as this is a bit of fun):
My car has gone from 135mph to 165mph (30 increase) by spending £279.00 on a remap. I am not the brightest bulb on the tree but I make that £9.30 per mph, or £2.31 per bhp; 158bhp to 279bhp
A modified auto 20i has gone from 142mph to 175mph (33 increase) for £10,000.00 (guess). I make that £303.03 per mph, or £81.30 per bhp; 181bhp to 304bhp.

I am Martin Lewis! :lol: oke:

 

[Mr Tidy]

Taking it all with a pinch of salt as it's just a bit of theoretical fun, but still interesting.

But as I put 45 section rear tyres on my MC the rev-limiter wouldn't cut in at 172mph in fifth, so maybe 177mph would be possible? The only certainty is that I won't be testing the theory - I'd miss my driving licence. :lol:

 

[sars]

I am sorry but I have to disagree... As you shift your engine torque will go up but the torque at the wheels will go down as the gearing has changed

Correct, torque at the wheels will reduce as you go from first to second, then second to third etcetera, however you still go faster every time you change up. The reason being that as long as there is torque then there is force and as mass doesn’t change you accelerate and go faster

As long as power in 6th at the RPM you'll end up at after the shift is lower than power in 5th at the RPM you were before the shift you'll end up slowing down :roll:

Wrong, because power is a function of torque and rpm, the equation is Power = torque x rpm/5,252. Engine torque peaks at x rpm and reduces there after as rpm increases, but power rises with increasing rpm (max torque is achieved at a lower rpm than max power). As you change up engine rpm drops for the same speed and thus engine torque is higher than before you changed gear. What you struggling to grasp is regardless of what gear you are in the power at the wheel is matched at engine rpm, i.e. at say 2000 rpm at the engine, the power at the wheel is exactly the same in second as it is in sixth.