28i vs E89 3.0 coupe bhp/torque didn't make sense?

[Smartbear]

Lol, yes engines are geared down, but a diesel is less geared down than a petrol, but not higher geared which means geared up, but yes higher geared down.....no that doesn't work either

Stop digging now
Regards

[mal_by]

No, torque and power are stated at the flywheel, not at the driven wheels so it is not just a function of torque it's also about gearing, a reduction gearbox increases torque but not power ( remember power = torque x rpm/5252)

A turbo diesel produces lots of low down torque, however they do not produce high rpm and thus the gearing is slightly lower to allow for the reduced rpm. Thus the torque generated at the driven wheel is usually less than its petrol bhp equivalent.

Hence modern 7 or 8 speed autos on Diesel engines are so good

^ exactly what makes diesels ultimately less "fun" to drive (that and the noise).

[techathy]

Thanks tech, I kinda get it. I think

Because the acceleration (0-60mph) is an average of acceleration that took place, acceleration at the point of max torque may not be the same in both car? And therefore my calculation is fundamentally flawed?

I've used data taken from real dyno pulls to generate this is thrust to weight ratio graph. As you can see the 28i spends most of it's time above the 3.0si except for right at the top end of the rev range.

0-60 the 28i records a theoretical 0.1s advantage between 5 & 60mph. It's all about the 1st gear pull. The thing is though, the 3.0si has a higher theoretical TV at 60 than the 28i, at 65mph the 3.0si pulls ahead and slowly widens the gap as the speed builds.

That's to simplistic and using power to describe acceleration is inaccurate, acceleration of an object is governed by it's mass and the amount of force applied to it, in other words the amount of torque at the driven wheel gives you the force. and then, well there are just so many factors that can shape the acceleration curve of a car, gear ratios, number of gears, spacing between gear ratio's, final drive, driven wheel diameter, tractability, engine torque curve, maximum rpm and etcetera

Enough of the variables are constrained that simplistic works here & I was trying to keep it simple for someone who hadn't quite got the concepts sorted in their head

[Twin Turbo]

As always techathy, great valuable input.

However this I believe will slightly change the perspective



As the torque figures have increased from 258 lbs @ 3300 to 275 @ 2900

And the green line - standard is very simular to the Manufactures guidance

[techathy]

Yay.. you've got an engine which is 1krpm away from being a diesel without the awful noise!

[R.E92]

As always techathy, great valuable input.

However this I believe will slightly change the perspective



As the torque figures have increased from 258 lbs @ 3300 to 275 @ 2900

And the green line - standard is very simular to the Manufactures guidance

It completely falls on its arse past 5k!

[Mister T]

I really hope the dyno operator let off the gas early on that run...

[EdButler]

Wow i've never seen a Petrol turbo look so... Diesely!

Did the tuner explain why it falls off a cliff? The stock power run produces more power over 5900RPM! I really wouldn't be happy with that - something looks wrong. I also wouldn't be happy with a before/after dyno without an AFR graph.

Could be heat-soak perhaps, exasperated by the higher boost levels (although if a tuner told that to me, id probably call BS!)

[sars]

That's an interesting analysis techathy, calculating specific force (N/kg) is by definition acceleration in each gear, doing it that way gives you a better picture of the cars real world performance than just using peak power and torque taken from the brochure

One thing the graph does show is how 3rd and 4th gear in either car gives reasonable acceleration over a wide speed range, makes for a relaxed cruising and how both cars are clearly geared for good 0 to 60 times

[Twin Turbo]

Hi,

I think it falling off an cliff is more to do with the operator - as below is an previous run - however they inputted the wrong settings so the numbers were incorrect - however it does show an improved flow for BHP, but Torque is SO WRONG.



To be honest, I am thinking of taking it to another rolling road center - so more information is provided

[techathy]

... and how both cars are clearly geared for good 0 to 60 times

With a 7k red line good 0-60 gears fall out of the woodwork for cars in the 250-350Nm range & 6 speed boxes. Lower the red line/limiter 500rpm and the gearing puts them a little bit bellow 60mph/100km/h.

TT, that still looks fairly rubbish torque wise. Was that a JB4?

[Twin Turbo]

TT, that still looks fairly rubbish torque wise. Was that a JB4?

Yes

[sars]

... and how both cars are clearly geared for good 0 to 60 times

With a 7k red line good 0-60 gears fall out of the woodwork for cars in the 250-350Nm range & 6 speed boxes. Lower the red line/limiter 500rpm and the gearing puts them a little bit bellow 60mph/100km/h.

That's a bit of a naive statement, if you had a slightly lower max rpm, engineers would alter the final drive to compensate. Designers work with what they have, low 0 to 60 times is marketing desirable and so they develop accordingly. For example you can see this philosophy between the 3.0si e85 and the 3.0 e89 in the 0 to 62 times, the e89 is heavier but the time taken for the 62 dash is identical for the manual with the same engine, the 28i manual has also identical 0 - 62 acceleration @ 5.7 seconds

[techathy]

It's observational analysis. Plenty of cars out there which miss out on 60 & 62mph by less than 5mph, & also have a marginally higher all important lower CO2 rating, where a simple final drive tweak could fix. But, as I found out with my 120dx there's a drivability cliff face - lower, even by a fair margin, isn’t a problem but cross the too tall line & you just fall off the urban drivability cliff. Those extra 500-800 rpm mean BMW's gearing tends to drop nicely into the 'just over' category while still being in the drivability range. This only applies to manual cars for the most part.

[sars]

and you just hit the nail on the head, why diesel cars in manual form do not make quick 0 to 60 times as a similar powered petrol car, which was one of the OP's later questions, which I explained some time ago and hence I return to my previous statement that it was more complex than you originally stated.