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Discussion Starter · #1 ·
Hello Guys,

I just wrote a small program for the calculation of a car's acceleration based on its power(@wheels),
gear ratios, launching revs, air drag, road friction ...
The only problem is that I need actual BHP [email protected]/revs to test it.

Is there any place I can find it on the web (I have tried http://dyno.scoobynet.co.uk/index.htm which has a few graphs from
VO's but only based on engine power and not [email protected]).

Any help will be appreciated.


Regards,


Alex.
 
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Discussion Starter · #2 ·
Yes, this is the website to a rolling road shoot out I went to.. My car is the only EVO 6 on it.. The rest are scoobys and Fords..

http://www.derbyshire-rsoc.co.uk/rrday/
 
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Discussion Starter · #3 ·
Thanks -Djack-,

Surprise surprise you car will do the 0-62 mph in about
4.35 ish secs (taking into assumption that you, your car
including fuel weigh 1430 Kg) doing almost a perfect start
(changing gear time was .2 secs bu you need to have a good
clutch and keep your foot down constantly even during the
gearchange).
 
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Discussion Starter · #6 ·
Chunky,

Cartest is not pretty accurate I am afraid (nor my program ofcourse).

Lat time I was using cartest it was giving me a 0-62 mph for the E6TME
at high 5's (with optimum launch). Apart from that I agree that its it a
very good program :)
 
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Discussion Starter · #7 ·
Alex,

Cartest is not pretty accurate I am afraid (nor my program ofcourse).

Cartest is fairly accurate if you spend time inputting the car-specific parameters. Its generic parameters are usually too generic (especially around power-at-wheels calculation) It's quite good for predicting the truth about which is the best rpm to launch from.

I don't normally bother with Cartest when trying to work out acceleration from a rolling start. It only took me an hour to knock up a spreaddie to do it at the weekend (CCC Claims thread) and another hour to make it really useful (i.e. calculating distance, losses due to gearchange). It's already told me that the Bruntingthorpe 2 mile straight should be plenty to try out my car's true top speed in March as long as I don't carry the same 4 fat bastards in the car as I did last time ;)

Ian.
 
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Discussion Starter · #8 ·
I've just read the 'CCC Claims' thread, sounds like the stuff I used to get up to in my old job (taught myself Excel by doing stuff like that)! ;)

Droid: Would be really interested in your sheet when you have it finished (or even a rough draft for now :)) [email protected]
 
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Discussion Starter · #9 ·
Chunky,

My latest spreadsheet is quite big (over 700k). If you don't mind getting that, let me know and I'll send it off to you.

Ian.
 
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Discussion Starter · #10 ·
Does this thing take into account things like only having FWD??? I have a few graphs of my Fiat Coupe I would be interested in knowing what the theoretical max 0-60 would be assuming I could get traction down, I have around 283bhp, 290lbft and 239bhp at wheels?

Not a Lancer I know but I am looking and the Coupe would be my other car.
 
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Discussion Starter · #11 ·
Droid,

I've spent quite some time with cartest long time ago feeding it with all the info
I had available for my E6TME and the best figure I was getting for 0-62 mph (optimum
launcing method) was at the high 5's region. I know that the person who coded the program
did an excellent job (a genuine attempt to) but I am afraid ther results regarding my E6's
performance were more than a bit out.

Have you tried it yourself ? My friend who introduced me to the program about 2 years ago used
to own a Z3 M and said that the program was producing quite accurate figures (with regards to his car).

Alex.
 
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Discussion Starter · #13 ·
Sandy,

If you tell me what is the weight of your car and provide me with the gear ratios (including the final drive) and
you car's drag coeeficient, I can run the program and give you ther results.

There will be several assumptions though (no spinning wheels, linear power through the revs, topped at 239 BHP,
very good clutch, very good gear changes) and what you'll get will be more likely close to the optimum.


Regards,


Alex.
 
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Discussion Starter · #14 ·
Weight of car with me and fuel is approx 1450kg, I know i'm a fat lardy.

the drag coefficient I am clueless about but seem to remember it was something like 0.3 but couldn't say for sure. Is it something I can work out?

Do you need tyre size, its 205/50x16, generally need to lauch at about 3000rpm to get the best out of it, but have to pay with the throttle a bit or it becomes a scrabbly monster.

ratios
1st 3.8
2nd 2.235
3rd 1.52
4th 1.156
5th 0.914
6th 0.816

final drive is 3.176

If its too much hassle don't worry about it two much I was just wondering. I realize there would be a few assumptions, just want to see how close I can get the car to its theorectical max when I next have a go.

Oh and if graphs are needed you will find them on my web link, sites a little crappy but there you go.

Cheers
Sandy
 
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Discussion Starter · #15 ·
Sandy,

Assuming that you have a linear distribution of power from 0 to 7500 revs (@7500 - and amp;gt; 238 BHP)
launching from 3000 rpm (with the perfect clutch, drag coeeficient .34, frontal area used 1.86 m^2,
you gearratios including final drive, 205/50x6 tyre profile) you will hit 62 miles at about 6302 revs/min
with 2nd gear in just over 4.4 secs considering a gearchange period of .2 sec (and during that gearchange
you would have to keep your foot still down on the accelerator).

The figure is indicative but can not be considered as accurate (no wheel spin is considered, 100% traction
is assumed).

if you could provide me with a few [email protected]/revs figures (let say 10 points point1: revs 3000, power 150, point2: revs 4000, point 175 ...)
I could give you a more accurate estimation.

Regards,


Alex.
 
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Discussion Starter · #16 ·
That should be a good enough indication Alex, thanks, don't think I'll be hitting 4.4 somehow, but its interesting all the same, getting under 5.7 is hard enough as it is, ah well roll on Lancer is what I say.

Cheers
 
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Discussion Starter · #17 ·
Sandy,

4 wheel drive cars have a great advantage on standing starts (almost twice the traction) but
a very good clutch and is also required to get close to the optimum figures. The official figures
quoted from ralliart (as part of the autocar test if I remember correctly) for the Evo6 (GSR) were
4.4 secs (which is a lot better too from what I have experienced so far with my previous E6TME).

I've done about 4-5 standing starts with my previous car and I personally don't believe that I
managed below 5 sec times.
 
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Discussion Starter · #18 ·
Alex,

The figure is indicative but can not be considered as accurate (no wheel spin is considered, 100% traction
is assumed).

That's the big problem with programs that estimate standing starts is that wheelspin/clutch spin is hard to estimate. I'm going to work on this over the weekend.

If your program really doesn't consider wheelspin then you'll be getting very optimistic results.

Folks ... there is NO such thing as a perfect start from reasonable rpm in ANY car. Fit whatever clutch you want, fit slicks and fit the strongest gearbox you can find but you can never get, say, 3000rpm from the engine down to the ground immediately (otherwise you'd be accelerating from rest to the equivalent of 3000rpm in 1st gear in zero time ... this is impossible). If you launch at high revs and get no wheel/clutch spin, the engine must be bogging down. If the engine doesn't bog down, you must be getting wheel/clutch spin. There's no way around this.

Re: Cartest

Yes, I've used Cartest for a long time now. Again, you're right that it's not very accurate if you use the standard parameters but there is a menu where you can fine tune some of the constants/assumptions that the program doesn't normally expose. If you do tune these (and this can take a while) you will get very accurate results.

Ian.
 
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Discussion Starter · #19 ·
Droid,

The program does not consider wheelspin directly but it does it by considering
clutch spin. For example if you are launching at 3000 rpm, the revs go down (instead
of going up) for some period until the revs at wheels reach the revs of the flywheel.
During that period the car is accelerating with a fraction (4/5) of the [email protected]
of the droping revs (although what happens in reality in a good launch is clutch slipage
while revs decreasing, clutch bites almost instantly with much slipage, revs increasing)

Droid with the 100% non sliping clutch launching at 3000 rpm with first the revs of the engine would
immediatelly drop to 0, effectively stalling the engine. Even if the engine wouldn't turn of by a miracle,
the power at those revs would be 0. What happens in reality in a very good launch is minimal spinning of
the clutch until the wheels reach the engine's revs.

We all know that there is no perfect start from reasonable rpm in any car (although batmobil tends to differ). :)
 
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Discussion Starter · #20 ·
Lee,

Sorry, missed your post up there. I've sent you the latest version ...

It's now officially the mutt's nuts :D and now models individual axle force (i.e. true 4WD modelling), weight transfer, wheelspin and amp; standing starts, distance covered, top speed, traction at individual axles etc. etc. Fed some numbers in for my M3, tweaked a little and got almost exactly the same numbers as Autocar's road test (including standing quarter and standing km). Cool.

Chunky ... I've sent it to you too.

Ian.
 
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