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      03-22-2007, 03:20 AM   #45
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Originally Posted by needforspeed View Post
Torque is the measureable rotational force which creates acceleration. You can ignore horsepower for the time being.

A vehicle will always accelerate hardest when torque at the wheels is highest. Torque at the wheels is a function of engine torque for a given speed multiplied by the effects of gearing.

BMW don't post in gear acceleration times for the 335d because it is only available as an auto. But it's in gear times WILL be faster than the 335i's, just as the in gear times for the 330d are faster than the 330i (in fact the 320d's are faster than the 330i).

This happens because turbo diesel engines create lots of torque, much more than petrol engines. Therefore most of the time, if you are cruising in a sensible gear - say at 70mph in 5th - the available wheel torque in a diesel will be greater than in a petrol car. That means it will accelerate harder in that gear - hence the in gear times.

The petrol car has an advantage though. It makes torque higher in it's rev range (which means it has higher horsepower). So in a 335i you would be able to drop to a lower gear than the diesel and hence multiply your torque.

So petrol cars ARE quicker, but only if you keep the revs high (in the powerband). You can't do this practically on the road, so in many situations diesels are quicker.

Great explanation here:

http://craig.backfire.ca/pages/autos/horsepower
Great explanation Simon. I experienced this at UK3. Paddy's 320d (chipped) was very hard to shake off, he could accelerate as quick as me and stayed on my tail all afternoon. The only noticeable difference was when I was in the higher rev range (redlining ) and I would pull away slightly but change gear and Paddy would soon be back with me!
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      03-22-2007, 03:22 AM   #46
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...but I do like to drive in a spirited fashion at times.
I NEVER drive in a spirited fashion...
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      03-22-2007, 03:38 AM   #47
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ZiM should be here in a bit, I reckon, talking about his old Integra Type R
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Wish I could have kept both..
Part of my thinking with the e92 was i wanted a fast, smooth, quiet, more business orientated car, and its excelled itself (btw, the break-in period is nearly done )

if i'd have gone for the petrol, it would have been because i'm trying to emulate my previous cars (petrol, manual, revs, all the funstuff), and for driving feel, i know it wouldn't have cut the mustard, sweet cars yes, but it certainly aint gonna handle like an integra/rx8/s2000 etc...

so i decided to go diesel for the first time in my life (a decision i'm more than happy with) and not try to compromise if you know what i mean, the plan is i now have the chilled out car (which albeit is a turbo monster ) - and to later get a high rev high fun no frills jobby... probably a lotus exige, but thats a bit down the line when the cash is flowing a bit more freely...

bottom line more on the topic of this thread, plant your foot in my car and you wonder what the hell hit ya! - the same in the 335i and you get the sound but the ole butt dyno doesn't give as good of a reading both great but for my purposes (and future aspirations) the d is the one.
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      03-22-2007, 04:33 AM   #48
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I guess I'm just getting old
I don't think that's the issue - it's really that as little as 4 years ago diesels were still pretty much rubbish.

It's only recent with the widespread advance of variable geometry turbos, common rail injection, aluminium blocks, piezzo electric ignition etc that diesels have really begun to worry high performance petrol cars.

A few years back we didn't have the option of this sort of relaxed torquey performance from anything other than a 5.0 litre v8.
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      03-22-2007, 04:46 AM   #49
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As has been correctly stated a cars rate of acceleration will be highest at the RPM its engine develops maximum torque.
Chris - I don't entirely agree with this, because you are ignoring the multiplication effect of gearing. This statement would only apply for vehicle with a single gear.

A cars acceleration will be greatest when torque at the wheels is greatest.

You can't understand relative performance without looking at gearing because this is fundamental to wheel torque.

This is explained really well in the 'complex example' given here:

http://craig.backfire.ca/pages/autos/horsepower
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      03-22-2007, 04:47 AM   #50
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Originally Posted by needforspeed View Post
I don't think that's the issue - it's really that as little as 4 years ago diesels were still pretty much rubbish.

It's only recent with the widespread advance of variable geometry turbos, common rail injection, aluminium blocks, piezzo electric ignition etc that diesels have really begun to worry high performance petrol cars.

A few years back we didn't have the option of this sort of relaxed torquey performance from anything other than a 5.0 litre v8.
My first 320d back in 2001 opened my eyes to modern diesel technology. All the diesels I'd driven before then were crap. By the way I still think BMW are producing better diesels than the competition.

I'll be at Le Mans in June where a diesel will probably win the 24 hour race for the second year running. It a shame BMW don't take part anymore as a diesel win would be great for them.

Regards

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      03-22-2007, 04:59 AM   #51
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But... the 335i can keep pulling to higher revs and so although it doesn't generate as much torque it can produce more power (by using high revs). But by then the diesel has hooked up the next gear to use it's superior torque to counter the petrol's superior revs.
This is where torque multiplication through gearing becomes important. The diesel can hook up to the next gear, but then the gear ratio will also increase.

This table illustrates torque multiplication for the 330i:



So for instance at 7000 rpm in 2nd gear you will be doing about 67mph. Your engine torque will be just 175 lb/ft, but wheel torque will be 438 lb/ft because of the gear ratio.

In contrast my 530d would have been in 3rd at 67mph, so it's torque multiplication would have been less.

This is why it is better to make torque high in the rev range (ie. have high horsepower) because you can gear it DOWN to multiply it more.
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      03-22-2007, 05:01 AM   #52
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i wanted a fast, smooth, quiet, more business orientated car


Zim, totally agree, that's why the rex had to go.. it did not suit the image of business I need to portray..

used to have to borrow the wifes car when i had to take clients out, not because I was ashamed of the rex.. but I found myself explaing my choice of car to them.. the 335I meets many of my requirements as you say.. fast smooth quiet.. I just got a little shocked with the amount of understeer it shows in tight corners...

and to the running in period.. been ragging it since day one.. LOL..

Back to topic..

NFS.. is spot on with the gearing aspects of Torque.. the Rex is a case in point.. on paper very low TQ.. but because of the gearing, never and issue in the real world..
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      03-22-2007, 05:30 AM   #53
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Originally Posted by needforspeed View Post
Chris - I don't entirely agree with this, because you are ignoring the multiplication effect of gearing. This statement would only apply for vehicle with a single gear.

A cars acceleration will be greatest when torque at the wheels is greatest.

You can't understand relative performance without looking at gearing because this is fundamental to wheel torque.

This is explained really well in the 'complex example' given here:

http://craig.backfire.ca/pages/autos/horsepower
I understand what you are saying about gearing, but in any particular gear that you happen to be in, the rate of acceleration will be greatest at the engines maximum torque figure. Thats's not to say that that if you were in a different gear your acceleration rate may again be higher. I think the thing about the diesels is the fact that you are allways very close to that maximum torque fiqure in every day driving, obviously the auto box and torque converter sees to that.

Btw the engine also produces its best specific fuel consumption (gms/bhp) at the maximum torque figure.

Regards

Chris
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      03-22-2007, 06:41 AM   #54
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Originally Posted by ChrisMWard View Post
in any particular gear that you happen to be in, the rate of acceleration will be greatest at the engines maximum torque figure.
I agree, but when comparing cars you really do have to consider the gearing, because it will have a dramatic effect on torque at the wheels - and hence acceleration.

Following on from your statement the maximum acceleration overal will occur at maximum engine torque in the lowest gear, because this is where torque multiplication will be greatest.

Gearing (and torque multiplication) is the reason why even relatively low power cars can pull away smartly up to 30mph.
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      03-22-2007, 07:35 AM   #55
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this thread has been a great read - NFS you should write a book

is there one of those tables about showing the same but for the 335d?
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      03-22-2007, 08:59 AM   #56
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this thread has been a great read - NFS you should write a book

is there one of those tables about showing the same but for the 335d?
If you can get me the torque curve and the gear ratios I will make you one.

Then you can work out if it's better to redline or short shift!
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      03-22-2007, 09:32 AM   #57
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Quote:
Originally Posted by needforspeed View Post
If you can get me the torque curve and the gear ratios I will make you one.

Then you can work out if it's better to redline or short shift!
aahh gocha, didn't realise you'd made it yourself...

i have no idea where to get a torque curve so dont worry about it cheers NFS.
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      03-22-2007, 11:04 AM   #58
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aahh gocha, didn't realise you'd made it yourself...

i have no idea where to get a torque curve so dont worry about it cheers NFS.
There's a torque curve and gear ratios for the 335d in the 3 series brochure.

Regards

Chris
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      03-22-2007, 11:18 AM   #59
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Yup, unless anyone comes up with anything 1st I can post the 335d touring figures tonight.
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      03-22-2007, 12:07 PM   #60
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To be representative as well you really need to include the final drive ratio so you get actual torque at the wheels as most of the 3s use different axle ratios.

Regards

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      03-22-2007, 02:33 PM   #61
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Originally Posted by needforspeed View Post
If you can get me the torque curve and the gear ratios I will make you one.

Then you can work out if it's better to redline or short shift!
Hi NFS. The closest data I can get is through a bit of measuring in the brochure and the gearing for the tourer:
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      03-22-2007, 03:21 PM   #62
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Phew.... I have just read thru the whole thread and its quite phenominal with regards to the science bit.

I am still none the wiser but it sounds that a DMS influenced 335d is the answer and that Beaufarty was in fact holding me up the other day!!

Chris & NFS keep it coming!!!
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      03-22-2007, 03:25 PM   #63
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Posted this before on the 320 chipping thread but seeing as you are so interested paddy

"Torque & BHP Technical Information

What is all this talk of torque?
Torque is the power of a rotating force, which is the product of one of two equal, opposite, and parallel offset forces and the distance between them. When this is applied to a car this means the effort exerted on a shaft to move the vehicle along. When torque is great enough to move a shaft through a given distance in a given time this is expressed as power and measured as horsepower.


Eh?
OK, if you have a centre nut on one of your wheels and then put a socket on it with a 1ft bar (bear with me on the imperial). The car will be at rest until you put a weight on the end of the bar to try and turn the wheel. So if you now put 50lb on the end of that 1ft bar and the car moves, the force that has moved that car from a standstill, at that speed, is 50 lb ft. So if the engine of that car produced the same amount of twisting force at its peak it would have been said to have a Torque of 50lb ft.

Now if you take that theory one step further and double the weight on the end of the bar and let go, the wheel would rotate again, only this time because the amount of force pushing the bar down was greater, the wheel would move off quicker and with more ease. Apply this once again to the engine producing the force and it would have been said to have a Torque of 100lb ft.

So you can see the more Torque you have the quicker the wheel would move off from stationary.

This is all fine and good on a light car as it means my 0-62 time will be decreased?
Yes the theory does indeed point to that, however do bear in mind that if a car produces 100 lb ft of torque and your car does 0-62 in 10 seconds, it is NOT going to do 0-62 in 5 seconds if you give it 200 lb ft of torque due to the inefficiencies of the engine, transmission etc, but it will be significantly reduced.


What about overtaking?
The samne theory applies to overtaking. The more force you can use to make the wheels go from say 50mph to 70mph the less time it will take to get there.

Why is torque important if I tow a caravan etc?
The more torque you have the more weight you can move forward from a standstill. Or in other words if the wheel you are trying to turn is stiffer it may not turn at al with 50 lb ft - it requires more force to turn it. Therefore if you increase the force by 50lb and the wheel turns then need 100 lb ft torque to move it. Apply that to a car with a trailer, you require more force to propel that whole unit (car and trailer) forward than you would with just the car. So once again with more torque you can move your car and trailer off from a standstill quicker and with less effort than you could before.


What about wheel spin?
With more torque available the quicker you can move the wheels from stationary. When this happens the wheels can spin before the vehicle has chance to move and you of course waste energy and move off slower. Therefore you need to alter your driving accordingly if the torque has been increased.


OK before I nod off, how is torque calculated?
The theory (oh no - not that word again!) is that torque has nothing to do with engine speed (revolutions per minute (RPM)). The torque figures depend on the mean effective pressure in the cylinders (MEP), which is calculated by taking away the total of the average pressures on the induction, compression and exhaust strokes from the average pressure on the expansion strokes. That's the theory.....

In reality the MEP (you should have read the previous paragraph) of an engine, decreases at high speed and the torque drops off. So the MEP is calculated from the Brake Horse Power (BHP) figures for an the engine, taking into account the inefficiency of the engine, so now the MEP becomes the Brake Mean Effective Pressure or BMEP, which is measured in lb in sq! Phew - that was easy.


BRAKE HORSE POWER

What is "Horsepower" or HP?
Lets start at the dawn of time - or at least the beginning of mechanical devices. Any "engine" was obviously going to be compared to the ability of the then main power sources to do labour - horses, men and oxen. As most of the devices were used drive industrial equipment the natural comparison was therefore the 2/1 Favourite at Ascot. So, even the pioneers of the time realised that marketing of the new fangled machin'rey was important so they likened the power of their devices to a certain number of horses.

Moving on from this early start, a famous engineer called Captain Thomas Savoury reasoned that if it took eight to ten horses to operate a mine pump 24 hours a day (two horse working at a time with the next pair taking over when the last two became tired), then a mechanical device that did the same job in the same time had 10 - 12 hp! You can move on through history with this through the likes of James Watt but you are not here for a history lesson!


So what is "brake" Horsepower or BHP
Well simply this is power that has been measured on a brake or normally known now as a Dynamometer. This device provides a load for the engine to "drive" against and then measures the torque produced by the engine, which if it is then multiplied this by crankshaft revolutions per minute and adjusted with the standard figure, it provides a horsepower figure "
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      03-22-2007, 03:51 PM   #64
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I might be on the wrong thread here but to let you all know i am new to the site and my 335i m sport coupe arrives next week.
Black Sapphire
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Should get the new 8 button i-drive!!!!!!!!!!

Pissed of about Gordon and his £400, but i test drove 335i and 335d and the petrol i found to have more soul, with the diesel's performance feeling a little bit surreal. Maybe because my current car is a Z4 3.0 (but i did own a 2001 330d before.) I think i have just been converted to a petrol head, but both are great cars.

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      03-22-2007, 03:53 PM   #65
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You could have started your own thread but no-one gives a crap in the uk forum . Welcome.
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      03-22-2007, 04:29 PM   #66
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I might be on the wrong thread here but to let you all know i am new to the site and my 335i m sport coupe arrives next week.
Black Sapphire
Saddle Brown
ali trim
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sun protection glass
dimming/folding mirrors
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DAB radio
i-pod i-drive interface
m sport kit

Should get the new 8 button i-drive!!!!!!!!!!

Pissed of about Gordon and his 400, but i test drove 335i and 335d and the petrol i found to have more soul, with the diesel's performance feeling a little bit surreal. Maybe because my current car is a Z4 3.0 (but i did own a 2001 330d before.) I think i have just been converted to a petrol head, but both are great cars.

Whats the new 8 button i-drive ?
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