Quoted Power Outputs

[Grumpyjohn1957]

With spring slowly approaching it’ll soon be time to get the winter tyres off and hopefully start enjoying some warmer days and tarmac. With a couple of club track days pencilled in for Brunhilda this year I thought it might be interesting to see what sort of power she’s producing.
I’ve spent a bit of time reading up on chassis dynamometers and how they work which is proving both interesting and quite technical. Essentially, you’re trying to back calculate what comes out of the crankshaft by seeing what is delivered by the road wheels. Seems a lot of assumptions get made in this process not to mention a host of variables requiring fiddle factors. To my mind there’s potential for a wide margin of error not least because of the way (or ways) in which the dyno rig itself can work but also with stuff like transmission losses, tyre grip on rollers etc. Using the same dyno rig and car set up whilst making adjustments you would at least see any improvement/detriment but how that actually/accurately equates to actual engine power I wouldn’t like to say.

The guy running the rig took great pride in telling me it was cutting edge, absolutely accurate, and cost £145K.

There’s much stuff on forums about performance boosting/chip tuning/remapping etc not to mention people extracting 600hp out of 3 Litre B58 engines in their garden sheds. Personally, I think its smoke and mirrors with tuning boxes, but a proper dyno remap can up the ante for sure. When folk get into fitting cat less downpipes, bigger turbos and intercoolers etc you can indeed build your own monster, but would it be reliable?
I’m sure Alpina & the M division have explored this to the “n”th degree concluding to get a reliable, drivable 500+hp from a B58 day in day out anywhere in the world 500/550hp is probably as far as you can push it.

The reality of UK roads is I can’t use what a stock B5 offers for more than a few seconds at a time without hitting highly illegal speeds. Most of the time I’m just happy to enjoy the torque but occasionally a few seconds of madness will creep in simply because I can.
I’ve seen a Germany company offering an OBD “tune” for the pre LCI B5 that takes it up to 720hp and 900nm there’s also a few 1000hp M5s about. All well and good but can the drive train take it? Hmmm, more modifications required! Other than bragging rights, why do it? I personally value my car too much to risk tweaking it.

Getting back to the subject of dynos. I assume Alpina base their power output numbers from engine dyno readings seen during test and development. They could individually test every engine before fitment, but I very much doubt they’d do that on cost grounds. To my mind and as conjectured by others our cars will produce no less than the stated figures suggesting most will give good few % hp more.

The quoted outputs of the pre/post LCI and the GT are interesting.

Pre LCI is 608 PS (not hp or bhp) or 447KW with 800nm torque.
Post LCI is 621 PS or 457KW with 800nm torque.
The GT is 634 PS or 466KW with 850nm torque.

Open the bonnets of pre/post LCI cars and there is a significant difference in layout. The inlet tract of later car is routed very differently with a balance pipe now connecting the intercoolers. (if anyone has a pdf of the Alpina LCI parts manual I’d love a copy) Apparently, this is where the extra power comes from as the engine can breathe more easily. I’d guess the mapping is adjusted to account for the extra air but it’s a seemingly mediocre lift in output for an otherwise identical engine. Having driven both models back-to-back I wouldn’t say the later car is any faster however the power delivery is far more linear across the rev range and way more responsive to a throttle prod.

I’m itching to have a good nose under a GTs bonnet and equally hungry to drive one. My guess is the extra grunt comes from an improved exhaust system together with a serious remap to turn the wick up. The stated increase between the models is very conservative & incremental at around 10 KW a step. However, looking at the performance figures suggests Alpina are either mega conservative or plain fibbing about the true outputs.

Putting numbers into 0-60 calculators suggests a B5 GT has at least around 486 KW or 660 PS. I know that on a cool dry day Brunhilda without launch control will dash to 60 in 3.2/3.4 seconds, a smidgen slower than the GT inferring her output is more than the official figure. On that basis I suspect the true power of a GT will be knocking on the door of 700 PS / 500 kW or more.

What did Mr Dyno say about Brunhilda?
Not 100% sure on how to decipher the numbers (have a look and tell me) the tech’ said she makes 654 hp/481kW with 919nm which is the higher of the red figures.
When quizzed about M5s they said its slightly more than the typical M5 CS without qualifying the slightly.
If correct I’d say not bad for an "as out of the box" magic carpet. Germans do have a sense of humour it seems.