[225]

Reading Evo earlier DMS were saying that M2s barely make the quoted 365bhp as standard but M4s make way over the quoted 425bhp :

The other reason I mention is that I had a spirited drive with an s5 and the old family estate passed it quite easily, obviously not that much faster but passed it everytime. Looking at the stats it has supposedly pretty much exactly the same power and torque so would have thought it would have been at least on a par?

[AlanYoro35i]

You also need to take into account
Weight/power ratio
When is peak power
Torque

BHP is only part of the formula. If you have a 500 bhp car that weights 2ton vs 1.3ton with 300bhp then it will be a close one. Also need to look at when power peaks. Most high power car makes most power on the top end, whereas diesel will give u lots of power from low to mids but nothing at the top.

Also depends on how power is delivered. NA car will pull away mostly at the top end whereas turbo cara will have lots of power throughout the range. Twin small turbos give most power at low to mid range but lacks top end power. Supercharge will get better power curves but no as good as turbo cars. Also when you have cars that has big turbo then power can start at the low end with peak near the top but you might get turbo lag.

It isn't so simply as looking what the quote bhp is on paper and that car will beat every every other lower power cars.

Also when reviews puts car on dyno , you also need to take into account that dyno's might read higher or condition is slight better than when tested. Example is bmw might ise 95 ron petrol vs when the punter who might put super. Air is cooler is also advantage and then the dyno guessing transmission lost rate might be different to what bmw put down.

[MattRST]

Exactly as above , and when you really get into figures it's torque @ the wheels which factors in gearing that really matters.

On most forums you hear quoted flywheel BHP and torque figures which don't mean a great deal

[Wills2]

It doesn't matter where or how a car makes its power as the gearbox will be matched to that delivery, in a drag race you'll be in the right gear to exploit the cars power band whether that is 2-4k or 6-8k.

Beyond a certain speed power counts (the ability to do lots of work at a high rate), a car with a superior PTWR will be beaten by a more powerful car even if it has a lower PTWR in terms of outright top speed. (BCGT with less PTW will out run a delimited F80 M3 for example)

But of course all the way along the line 0-XXXmph various factors come into play with either greater or diminishing influence Traction/PTWR/Frontal area/Power/Gearing.

I also do not buy in to the theory that BMW is giving us free additional power.

[JD6]

I tend to think that the standing quarter mile is a pretty good representation of how fast a car is, and gets around the bull$hit you can get from rolling roads. It is rather hard to skew a quarter mile. Of course it also nicely illustrates just how much faster an M3 is than any of the ordinary 3s.

Have there been any 340is turn up for the standing quarter events yet? I would be interested to see how they do.

[225]

Yes well aware of bhp per tonne etc effects performance. As an ex tvr driver I am well used to "optimistic " power outputs however any way you cut it TVR s were light! Just it seems no one regulates the quoted figures.

[Wills2]

Originally Posted by 225

Just it seems no one regulates the quoted figures.

Most if not all the major manufacturers do to SAE standards on an engine dyno.

[JustChris]

I have long assumed now that all quoted figures are under rated to avoid a class action lawsuit situation.

Then it's just how much they are under rated, Porsche seems to be very and BMW a bit?

[Wills2]

All depends on the measure, when someone lifts an engine from an M5 and takes it to somewhere like MIRA and rates it on an engine dyno then we'll find out, putting it on a rolling road isn't the same thing.

[MattRST]

Originally Posted by Lobb

Exactly.

Which is why the torque outputs quoted for diesels are meaningless.

Spot on and why the later generation diesels with an 8 speed drive better

[Wills2]

Originally Posted by Lobb

Not DIN?

DIN being the German standards body to SAE which is IIRC is more global.

The difference being the "scales used" but yes I'm sure some use DIN especially in Europe rather than SAE

Either way the HP our cars produce is tested properly under their rules, but people seem to trust the guy with rolling road or their own bum dyno instead.

[snipnoob86]

I guess having the figures and data for a certain car / engine can be interesting but we'll it transfers that power to the road is the magical bit. some are better than others