How fast can an E89 go? Part Deux!
- Thread starter B21
- Start date
sars said:So I've had a little time during a wet lunch to put pen to paper and reacquaint myself to Massey, Bernoulli and Mr Watt! When B21 put the above graph together I thought he's got an answer after a fashion and in a round about way, so: -
Screenshot 2022-02-15 172604.png
This is an amalgamation of two well known formulae derived from Bernoulli and Watt, there are limitations to the theory based on low Reynolds number, where inertia of the fluid is ignored, but for our Zeds it's simple enough. Though it does ignore rolling resistance, friction of bearings etcetera.
For my car the theoretical top speed not limited by gearing with a Cd of 0.35, frontal area of 2.2 m2 and 250kW, is 79 m/s or 178 mph
Never mind wet lunch, Sars....
With all that kind of talk you'll be giving b21 wet dreams,lol
I can make a spreadsheet, though I need to know the Cd and frontal area for the three models, I took an estimate on frontal area and I think the Cd figure seems high, probably given for the top down.B21 said:Splendid..the sim suggests 175mph..now that you are on a roll could you do a time, distance to top speed model please ?
mcbutler said:
If you look at the graph your car (broadly same as mine) and the power curves then at around 120 mph you need about 100 wheel bhp and at 4,000 rpm ish you have over 200 wheel bhp spare..so your car will accelerate from 120 like a 200 bhp car would from rest..(for a while)
You are just coming off the peak of the torque curve so all the stars align..that's why a 35is is such a great motorway blaster.. :driving:
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sars said:I can make a spreadsheet, though I need to know the Cd and frontal area for the three models, I took an estimate on frontal area and I think the Cd figure seems high, probably given for the top down.B21 said:Splendid..the sim suggests 175mph..now that you are on a roll could you do a time, distance to top speed model please ?
sars, here is the normalised data as best as I can do it.
Few comments /observations..
I've included the US version of the M40i to see how the extra BHP affects the calcs, and on my 35is as well as the BHP increase I've used flybobbie post on aerodynamic devices to reduce my drag factor...on there model which had a drag factor of 0.3441 which is in the Z4 ball park, the spoiler and diffuser had a reduction from 0.3441 to 0.2872 ie 0.05 reduction..I've taken a 0.03 reduction for less than perfection.
Interesting that the M40i has the same spoiler and diffuser design, more or less.
Also my wheels / tyres are 1.9% larger hence higher theoretical top speed.
I've assumed transmission losses are equal..in theory the Z4M manual box and the 35is DCT box should be close and they are both in direct drive, the Z40M is in 7th which is in-direct so in theory there should be a little extra transmission loss.
Weight is required for my rolling resistance calculations..I've taken GVW and subtracted 150kg for no passenger and luggage (also addresses the options as they are not often factored into the empty weight calcs)
Over to you!
There's a link to an excel spreasheet here..
https://www.dropbox.com/s/ykl3hkkrut8rxyn/Another%20speed%20calculator.xlsx?dl=0
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buzyg said:Just need for Beedub to give us the BHP figure for his MR roof up now and we will have a theoretical winner. :evil::wink:
Yes that would be good..the more the merrier...given that the stock Z4M in 5th is over-revving to get to 176mph then in top gear with all that extra power it should pull comfortably..ideally a dyno print out would help.. :driving: :driving: :driving:
B21 said:tiglon said:
Your car is definitely faster than mine..respect.. :tumbleweed: :driving: :rofl:
You say that, but the "Fear" number is highly variable, and may increase dramatically when I'm travelling at high speed on the Autobahn compared to being sat at a desk in England...
So I've done some calculations for you, though I think they're a little optimistic :wink:
The F40 was the first production car to break the 200 mph barrier, with a Vmax of 201 mph from 351 kW, Cd = 0.34 and I've estimated the frontal area at 85% of the width x height (1970 x 1124) which gives a theoretical Vmax of 207.8 mph, 6.8 mph over published giving a calculated theoretical Vmax accuracy of 96.6%.
Therefore giving the same accuracy for your car, it's Vmax is, drum roll please
195.1 mph.
but it's not the fastest Zed I'm afraid, there's a G29 with +400 hp on here and then there's that pesky supercharged M
The F40 was the first production car to break the 200 mph barrier, with a Vmax of 201 mph from 351 kW, Cd = 0.34 and I've estimated the frontal area at 85% of the width x height (1970 x 1124) which gives a theoretical Vmax of 207.8 mph, 6.8 mph over published giving a calculated theoretical Vmax accuracy of 96.6%.
Therefore giving the same accuracy for your car, it's Vmax is, drum roll please
195.1 mph.
but it's not the fastest Zed I'm afraid, there's a G29 with +400 hp on here and then there's that pesky supercharged M
sars good attempt…
I found a couple more accurate calculators and I then took some dyno runs of N54 powered cars that did both crank and wheel hp, so used these correction factors..the results are here..
I took into account the gearing, the best gear to do the job and the actual power curve to determine both the theory if yiy ignored these issues and the most likely realistic outcome if you did enjoy.. :
So obviously all ridiculous speeds although I did find a EU spec M40i that was mosselman tuned hitting 180mph pretty effortlessly on YouTube.
It does look like a supercharged Z4M or a more aggressively tuned M40i will take the honours…the 35is hasn’t got the gearing on these turbos to do much more, it’s running over the peak. We will have to wait to see how the TTE500s do, if they allow it to rev to close to the red line then it could give a supercharged M or a tweaked M40i a run..but at the moment on the Forum I think the supercharged M will be topdog :driving: :driving: :driving:
I found a couple more accurate calculators and I then took some dyno runs of N54 powered cars that did both crank and wheel hp, so used these correction factors..the results are here..
I took into account the gearing, the best gear to do the job and the actual power curve to determine both the theory if yiy ignored these issues and the most likely realistic outcome if you did enjoy..
:So obviously all ridiculous speeds although I did find a EU spec M40i that was mosselman tuned hitting 180mph pretty effortlessly on YouTube.
It does look like a supercharged Z4M or a more aggressively tuned M40i will take the honours…the 35is hasn’t got the gearing on these turbos to do much more, it’s running over the peak. We will have to wait to see how the TTE500s do, if they allow it to rev to close to the red line then it could give a supercharged M or a tweaked M40i a run..but at the moment on the Forum I think the supercharged M will be topdog :driving: :driving: :driving:
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Would that mean a small weapon?john-e89 said:sars said:[ref]Argyll Andy[/ref], did you see anywhere within that equation for a car colour coefficient multiplier
[ref]john-e89[/ref], The chances of you getting lucky on a date is proportional to the mode of transport in which you pick me up for that date, I’m thinking that a mobility scooter might not quite do it :lol:
Fear not fair wench....I have other means that'll take thee verily breath away....
B21 said:buzyg said:Just need for Beedub to give us the BHP figure for his MR roof up now and we will have a theoretical winner. :evil:
Yes that would be good..the more the merrier...given that the stock Z4M in 5th is over-revving to get to 176mph then in top gear with all that extra power it should pull comfortably..ideally a dyno print out would help.. :driving: :driving: :driving:
Pretty sure Beedubs car is circa 550bhp at full boost.
john-e89 said:B21 said:buzyg said:Just need for Beedub to give us the BHP figure for his MR roof up now and we will have a theoretical winner. :evil:
Yes that would be good..the more the merrier...given that the stock Z4M in 5th is over-revving to get to 176mph then in top gear with all that extra power it should pull comfortably..ideally a dyno print out would help.. :driving: :driving: :driving:
Pretty sure Beedubs car is circa 550bhp at full boost.
And a touch under 1400kg :evil:
Argyll Andy said:john-e89 said:B21 said:Yes that would be good..the more the merrier...given that the stock Z4M in 5th is over-revving to get to 176mph then in top gear with all that extra power it should pull comfortably..ideally a dyno print out would help.. :driving: :driving: :driving:
Pretty sure Beedubs car is circa 550bhp at full boost.
And a touch under 1400kg :evil:
And utterly mint....pics don't do it justice...! Quite glad I didn't buy it a few yrs ago as I'd have had to sell it back to him as once you see it in the flesh you can't keep a car like that away from its creator.
