To have the straight line speed of a BMW M3 e46?

Erm, what's the straight line speed of the BMW first ?

Or was this a homework type question where we have to do the research for you ?

Lol.

I don't really know the straight line speed of an M3 in the real world. 0-60 is not particularly relevant in my mind. 40 - 80 would be better, but you don't see that information published much.

I suppose I am being a little lazy, but other people might be able to give a better answer off the top of their head than I will get after 15 mins of research, so I thought I'd ask the question!

452.3Bhp, but I can't show my workings......

I thought it was 452.4 but Stan was always better at mafs then I was.

You would need exactly ...

295bhp

295, really. That's actually not that much. Guess the weight of the coupe makes a big difference as the M3 has about 340bhp?

So what sort of modifications does that translate to
hybrid turbo,
small FMIC,
custom map,
sports filter;
boost control?

Weight is completely irrelevent for top speed, although it obviously has a huge effect on acceleration

The M3 is quick, no doubt about it, but spend a couple of grand on a healthy Coupe and you'll be able to hang onto it as long as there's no corners.

As soon as there's a bend or three in the equation, the Coupe will need rather a lot more spending on it (either to let it keep up in the corners, or to make it fast enough down the straights to make up the cornering defecit)

There was nothing in it between my old Coupe and an E46 M3 (in a straight line), I had just over 300 bhp.

From 95-140mph theoretically indicated, somewhere between 315-342bhp is enough to put 7 lengths on one

Ive owned both and there doesnt *feel* like there's much difference between the two in a straight line...although ive never had them up against each other side by side, there's a lot of difference in the way the power is delivered though...even a lightly modified coop is definitely stronger in the mid range and in-gear acceleration, the M3 is better off the line and higher up in the rev range...so to answer the question i'd say anything up to 260-270 is enough to be neck and neck.

Ok... I've actually worked this out!!!

Bearing in mind the bmer is rear wheel drive and the coupe front I got a relitive, real-world acceleration value by deducting the 0-60 time from the 0-100 time giving a 60-100 time. I then converted this into m/s and then divided this by the time for each car to give the acceleration m/s/s or m/s^2. Then using the calculation F=Ma (force = mass times acceleration) I was able to calculate the force produced by each car in order to achieve that acceleration. Then I divided that value by the KW powe of the car as power = ForceXRPM and this gave an inverse of the RPM which can be used as a relitivistic constant for each car which should allow for transmission losses.

Then by substituting the acceleration of the B'mer into the coupes equasions and working them back I was able to extrapolate the required KW power needed to make the coop as fast as the B'mer then I converted it into PS and it was:

265PS
So you only need to add 45BHP to a standard coupe to make it as fast as a B'mer from 60mph to 100mph

Yes I can show my workings out too


I'm taking this as validation of my workings out!

You didnt take wind resistance into the equation.

The BMW has more power pushing against the air resistance, so the faster you get, the weight of the car plays less and less of a part. You need about 290-300 bhp in a Coupe to match the BMW at 100 mph.

Same reason my MX5 will out accellerate a non turbo Coupe at 20 mph but has a lower top speed.

9ooo million and 6 pikies with their horses and dags
Oh.....wind resistance.......less one dag......that should do it
For my next joke.....an MX5 is very fast....boom boom

What on earth are you on? You truly are an odd ball

I've got a lot of respect for this work - it's a great bit of logic and application (although I will not claim to understand the detail).

265 is a bit less than I thought. I was expecting that given the M3 weighs about 270KG more than the coupe, but has an additional 120 BHP, that the answer would lie somewhere around the region where the power to weight ratios level out.

Taking the data from TorqueStats:
BMW - 1577KG (1.5520936940425472 UK ton) with 343BHP; and
Coupe - 1310KG (1.2893105511704102 UK ton) with 220BHP,
my reckoning is the coupe needs to make 185 BHP to give it the same power to weight ratio as the M3.

Now, obviously this does not take into account transmission losses, wind resistance, gearing ratios etc. Question is though whether these differentials between 40 - 80mph account for a 20BHP advantage toward the coupe?

Thoughts?

Do you guys think I pull my numbers out of my 4rse? I've added considerably more factors into my spreadsheet that I often quote numbers from.

Here's a basic run through of how it works;

By running co-efficient of drag and frontal area (CDA) through some formulae, I worked out what bhp is required to maintain x mph for a given object (in this case a car).

By then running a Vlookups over the car's gear ratios, I was able to work out the gear the car would be in at x mph. From this speed I could tell what gear the car is in and from this, I worked out the rpm of the vehicle’s engine. With the rpm known, I can work out the current bhp @ wheels from dyno results.

Taking the required bhp at x mph from the current bhp, allowed me to work out how much power remained for pure acceleration. I did this for every 0.1mph increment on my spreadsheet.

Using remaining power and weight, I can work out the accelerative force and, using this, I worked out the time it takes to accelerate over every 0.1mph increment from staionary to top speed. The cumulative distance can easily be calucaluted from this (as can the cumulative time) for any increment (30-70, 100m@ 70mph- 1014m, 0-321m, and so on)

To work out top speed, I asked excel to bring back the speed when the accelerative force = nill.

The ONLY factors that it doesn't include are (aside from silly things like incline or weather) drag from tyre friction, downforce, lift, variable transmission losses (such as gearbox oil heat).

I was not suggesting anything of the sort trappy. Clearly you pull them from a spreadsheet!

That said, my question was driving at what BHP would a coupe need to run to achieve the same 40 - 80 times as an E46 M3 (i.e. real world performance).

Your answer was on what BHP I would need to pull 7 lengths on one between 95-140mph.

Steve

To cover an equal distance from 40-80mph, a 20vT would need 275bhp. That's not to say it will be as fast before or after this increment though, and remember that a 20vT changes into 2nd at just after 40mph.

So the maths concurs with my butt-dyno!

I've started working on a detailed explanation of performance and how it relates to power. It will hopefully put the whole bhp/tonne thing into perspective and show exactly why that just because one caar is as quick (or even quicker) than another from say 40-80mph, it won't be anything like as quick from 100-120mph.

It's all about and 'remaining, power for acceleration after areodynamic drag'. I've found that a lot of the results of my calculator can go a fair way of explaining a lot of the 'taller tales' we used to see in the 'Coupé vs' section.

I'd be interested to see that.

In your last sentance are you alluding that, when it comes to real world acceleration, the coupe is pretty quick, relative to it's BHP?

For me there is not much point in being able to accelerate quickly above 90mph as I very rarely go faster than that and when I do I am not looking for spectacular acceleration.

I'm sure Trappy will agree with me when I point out that peak power - or even peak torque - is utterly immaterial when it comes to calculating speeds and accelerations.

What you care about is the specific wheel power at a given speed; it's the area under the curve that matters, not how tall it is.

I'm suggesting that sometimes a car that looks considerably faster on paper can appear slower when put up against another, slower car in certain circumstances. Putting you foot down a split second earlier than a 500bhp merc in a 270bhp coop and having a blast from 60-90mph and seeing 'not-a-lot' happen might make you think your car is a match for such a beast when in relality, the gap is enormous. The same can be said of putting said coop up against a Clio sport from 40-85mph on a track.



This is spot on barnacle. More specifically, it's the power available when chasing through the gears that counts. You want the highest part of the power curve between the revs you're at as you change up, and the redline. As you were alluding, 275bhp at the wheels, right across the curve will give more acceleration that 240bhp rising to 285bhp at the redline; it's the mean that counts.

Another thing to consider is the transimission losses. Some cars might gain bhp in their curve at the same rate that the losses go up, giving a very liner power delivery. Most modern hot hatches make their most power over 1,300rpms before the redline resulting in a trailing power curve that is further compounded by higher transimission lossese, meaning the actual force pushing the car forwards decreases as the speed rises in each gear. It won't neccessarily make the car slower (as I said above, you more mean power you have, the more acceleration you'll get), but it will feel like a diesel- which is exactly what they do, just to an even greater extent.

I've yapped on long enough now methinks... When I'm boring myself, what chance do you have!

you need around 260-280bhp but matching lbs tq as i had a seat leon mk1 cupra moded to 254bhp and 257 lbs tq and beat it by 2car lenghts from 40mph to 130mph then had to slow down...now i got a coupe running 270-280 bhp and was half a cars lenght behind a 360bhp subaru sti on a rolling start

<moderator hat = on>

Please remember that discussion of racing on the public road, aka 'vs' posts, are strictly forbidden on this forum and will lead to deletion of offending posts without warning.

Thanks.

<moderator hat = off>

Who gives a monkies, if one "gives it" along side you plant your foot down and see what happens!

Fair enough, just don't post it on here :-)

Trappy,

Given your comments above about gearing would you mind providing the BHP figures for

30-70
20-50

as well?

Again, to give an E46 M3 equivalent coupe?

Next time I see you at Rog's perhaps you will take me for a spin in your coupe so I can feel the power - never been in a modified car?

Thanks
Steve

20-50mph. E46 M3 1.9s
You aren't going to beat an M3. Using road tyres the M3 can simply put down more force. The coop's low down speed is limited, and as you increase the power, you increase the 'feathered throttle period'. You see my calculator gives every car a max force it can deploy. For the coop it's 5.13Gs, the M3 5.99Gs.

30-70mph. E46 M3 4.4s
It isn't possible to give a 'required bhp to match' because of the reasons Barnacle and I outlined above. It's even more complicated than that though as the mean power needs to reflect power that is being affected more and more by drag. It would be fair to say that 265bhp might be enough to level peg with an E46 M3 from 30-70mph, but as the speed of the increments rises, the required power also rise. Hence to match the M3s top speed of 168-173mph, you'd need to modify the gear ratios (or rev limit) and be making around 310-315bhp at the fly at the redline. Of course you's then hammer the M3 from 40mph on though.

When you have two cars with different CDAs and different weights, there is no way you can make them perform the same from standstill to top speed. The closest you can get is an overlap somewhere in the middle.

(power@wheels-aerodynamic drag)/ weight

That formula explains it all really.

Just let me know when you're booked in over there on a Saturday. I'm only 10 mins away and can usually spare 30 mins so I'll pop over and take you for a spin

For those of you doing all calculations to work this out seriously man get a life or a girlfriend... lol

Id say 300bhp on the safe side.

Just ask this guy http://www.youtube.com/watch?v=cpoa9iFabD8

Thats an early model 3.0L E36...quite a bit of difference in performance to an E46!

Well it's not an BMW M3 E46, but this is what is required for a 2005 Mercedes E55 AMG @ 480bhp

Amazingly, I have a life, a family, and a full time job, and yet I still manage to find time to create a calculator to shed a little light on the subject of many petrolheads' questions that arise on motoring forums.



If that is your estimate as to the required peak bhp to give a 20vT the performance of an E46 M3, then you'd be wrong for the reasons I've outlined above.

Truely massive performance from the coupe there. I love our cars.

dyslexia sucks