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      08-13-2014, 02:16 PM   #15
Boss330
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Quote:
Originally Posted by FogCityM3 View Post
Very interesting and appreciate the time/effort put into this analysis.. A few observations:

1) RRI dynos for the S65 at the hub with full wind tunnel/heat exchange effects. Adding tires/wheels will increase drivetrain losses, more along lines of 14%-15%, which may serve as a closer starting point for subtracting loss effects.

2) I’m extremely surprised that no one uses the BT tool to log “Actual Moment”, which is what the ECU’s calculation of torque hp is based on all available parameters. One would think this would be an extremely accurate measure of bhp (unless BMW’s calculations for its own ECU are wrong). In my own logging, this corroborates very closely with Dash Dyno results (see below) and while I have only logged the only the S65, it shows that it is neither under or overrated, and that changes in fuel quality (ie race gas and E85 mixtures) have a direct affect on bhp produced.

3) Have you looked into Dash Dyno, http://www.auterraweb.com/dashdynoseries.html on on-road dyno tool. In addition to entering a bunch of parameters (some are also calculated ie drivetrain losses) there is also a correction factor that you can apply to the speedo (using gps). Assuming a 13%-15% drivetrain loss, I get nearly the exact same bhp results as using the Actual Moment calculation from BT (this calculation must be converted to SAE and is simply a raw number).

4) Dyno room conditions, full wind tunnel effects, IATs vs ambients, atmospheric pressure, fuel quality, all effect A/F, timing, and ultimately power produced. Every time I’ve seen BT logs for the S65, they look nothing like what I see on open road logging and hence I believe that most S65 dynos show improper underrating. The dynos showing BT logs that I’ve seen show rich A/F and significant timing pulled (8-10 degrees). I don’t know why more BT logging isn’t used where you can keep track of ambient conditions, engine performance parameters and how they affect the actual moment/bhp. For example, I know that race gas mix vs 91 octane consistently adds 8- 10 bhp. E30 Mix adds 20 bhp; every -30 change mpar pressure ~ 5bhp. I know the S55 will adjust for these conditions and produce more consistent power, but the S65 dynos I’ve seen understate results except for 2 of them: Dinan and Rototest, which show the engine to be rated about where it should be from the factory –and surprise those are the two dynos that best replicate ambient road conditions and full heat exchange. Dinan has also engine dyno’d the S65 in developing its stroker engines and also, it is not overrated/underrated in stock form.

5) Eventually Dinan will likely engine dyno the S55 and will be interesting to see the results. So far, what they’ve seen with the N55 (engine dyno’d by Dinan) is that it is less than 2% underrated.
Thanks, and agree with using the immense amount of data available from the OBD port. Probably the most accurate way of getting performance data!

And, as a engineer working with modifications of vehicles and EU-type approval procedures, it seems incredible to me that BMW deliberately misleads EU authorities by stating a false engine HP number...

BTW, the engines are also dyno'd independently by a technical service (usually TÜV) for type approval purposes. The manufacturers claimed HP/TQ numbers are accepted if they are within 5% of the manufacturers claim, on the dyno (engine dyno).
Appreciate 0