[P1 Motorcars]

Originally Posted by bruce.augenstein@comcast.

One question, though. Why would you be using SAE corrected dyno results?

We did this to follow proper CarTest procedures. CarTest documentation instructs us to use SAE corrected numbers.

HORSEPOWER: Enter the peak SAE standard J1349 measured net horsepower and the engine rpm at which it is developed.

HORSEPOWER CURVE VALUES: If you are using car-specific parameters, you can override the idealized engine power curve shape that CarTest prepares with the exact engine power curve if it is known. ... All data must be SAE corrected.

CarTest is trying to simulate performance based on real world conditions. Therefore it applies its own (SAE) weather correction to the dyno charts we input, from the new weather we input into the program. This is why we think CarTest makes this requirement.

Do you have facts that support the idea that the S55 engine doesn't already correct itself? That is to say, it makes 425 HP over a wide range of weather conditions (including altitude), automatically correcting itself to an SAE standard day.

This isn't our subject matter or expertise. But I still might be able to help. There are four bone stock dyno's in the Dyno Database. One of them is our own. If the S55 ECU can correct for weather to ensure it always has the same rated power regardless of weather conditions, then the UNCORRECTED dyno results should always be nearly the same regardless of conditions.

Here's the graph. You be the judge if these all look the same. Even though our results are in the Dyno Database, we excluded our own results because they are clearly outliers. Our car had less than 100 miles on it and we didn't even take it to redline. But if you want to download and look, they're in the db.

Originally Posted by Boss330

Would like to know the reasoning behind adding SAE correction on an engine that, according to what BMW have told us, is capable of correcting itself for "non SAE" conditions... You just can't add SAE correction if the engine already has corrected for the "non SAE" conditions!

Interesting to see what your opinion is of the uncorrected dyno's above. SAE correction is selected as per CarTest instructions.

I'd say the case isn't closed quite yet. Just in the SAE corrections that has been done here, there is potentially a substantial error in the claimed "facts"!

As you said; Garbage in, Garbage out...

The SAE correction conditions are documented in the Dyno Database, and the dyno files are available for download. Here's a recap of what they show. I'm not sure if this is what you consider significant or not.

SAE correction for stock conditions:
Temp: 77.88
Pressure: 29.07 inHg
Humidity: 33%
Correction: 1.021
Uncorrected horsepower: 411 whp
Corrected horsepower: 420 whp

SAE correction for JB4 Tuned conditions:
Temp: 79.52 deg-F
Pressure: 29.10 inHg
Humidity: 30%
Correction: 1.021
Uncorrected horsepower: 461 whp
Corrected horsepower: 470 whp

Since we documented all of our input parameters to CarTest (except two), you are free to use our values. We welcome people checking our work, or pointing out any errors we made with our input values. If the previous CarTest article published this data, we believe we would have been able to point out what was wrong with it. You are free to verify our results and download the files from the Dyno Database just as we did, change to uncorrected horsepower and see what you get.

Originally Posted by FogCityM3

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.

That is not the correct way to do this. CarTest has separate tire and drive train loss calculations. You're proposing to add tire losses to drive train losses. That would add a double correction and would be incorrect. You can see what I mean in the following graph. This graph from CarTest shows separate wheel and drive train (transmission) losses.

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.

The BT tool doesn't have F8x support yet (we tried), and the Actual Moment isn't accurate anyways. Here's a graph from that shows this inaccuracy. The first graph shows the actual dyno. The second graph shows a comparison between what the actual dyno saw vs. what the ECU "Actual Moment" saw at the same time.

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).

Nope, we haven't tried it. It looks pretty cool. I'll look over the web site technical data and give an update if you're curious what we think. It's worth noting that the math they use to calculate horsepower should be the same thing the vBox Dyno does. The formulas are well established physics formulas. So if you believe in the Dash Dyno, you should believe the vBox Dyno as well.

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.

Interesting to see what you think of those uncorrected dyno's as well.

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.

Dinan uses a Motec ECU on the engine dyno. You can't look at their engine dyno results and tell anything about under or overrating. It is not running the same software as your car.

Originally Posted by Boss330

Could very well be, but SAE corrections has been proven to be a quite big factor (in one instance for example 40hp). A correction factor of say 40hp for a given atmospheric condition is a lot of noise...

Here's how to put that into perspective. SAE correction is only valid for +/- 7% correction value. At the maximum 7% correction, the minimum whp required to cause a 40 whp swing would be approximately 612 whp. But more to reality, I just checked the S65 dyno database and see the maximum recorded SAE correction (that doesn't violate the +/- 7% spec) was 3.4%. It would take approximately 1175 whp at 3.4% correction to cause a 40 whp swing. Curious if you have any links to the 40whp correction swing you mentioned?

I'm not saying that I have the final answer or know all the answers. But I am quite certain that the trap speeds we have seen so far really doesn't indicate a under stating from BMW (or at least not more than the 5% margin they are allowed by EU regulations).

I don't know about EU regulations and that's not our area of expertise. But I am curious what you think of the vBox Dyno calculations. At the end of the day, we're pretty sure all horsepower calculator uses the same physics formulas as used by the vBox Dyno, and you can see from the vBox Dyno description it does a helluva lot of calculations and has very fine control of the input parameters.

It's also interesting how the OP is critical of the shortcomings of the Insoric and dismisses the results that gave (which didn't fit in with the OP's other "findings"), but seems to forget the shortcomings of dyno's and the inaccuracies shown again and again on dynos... The OP accused the other "author" (swamp2) of just using data that fit in with his views, seems to me there was a bit of that going on here instead

I'm not sure I follow you here. I think you're talking about comparing Dyno Brand-D to Dyno Brand-B. We've only modeled CarTest based on Dynojet results, so that's the only thing I can really vouch for our methods, accuracy, and results. If you have other verified examples of dyno's + vBox results from the same car, we will be happy to perform the same test and see if we get the same results. PM us for details if this data is available.

Originally Posted by Alex07M3

Is the 480-500whp JB4 tune used in your test's the same as the one used by this M4 that seem to be about equal with a stock 460bhp Stingray!?
http://f80.bimmerpost.com/forums/sho....php?t=1020694

No, Terry Burger is based in California and uses 91 octane, that car (if it's the OP's car) is based in MD and used 93 octane. I also don't think Terry does street racing.

Originally Posted by KennyPower

first of all, there is no guarantee that the m4 's adaptation actually works to correct to exactly 100% of stated power in any conditions.

Also curious of your opinion of the uncorrected dyno results. BTW if anybody has any more bone stock F8x Dynojet files, I'll be happy to add them to the uncorrected graph and see how they compare. And if anybody has any dyno's + vBox results, I'll be happy to run the same tests and present the results no matter what they show.