Feedback on dyno results - what's wrong here? - The Unofficial BMW M5 Messageboard (m5board.com)

cosioboy · 10th July 2006, 00:54

OK, so I finally went to get a dyno measurement, but left severely dissapointed. I am pretty convinced the car is top notch, especially after the Powerchip 93 I got about a month ago, it has never felt stronger. I expected at least 340 atw factoring some of the mods, considering that is what most folks get on a pure stock Beast. My MAFS test is in the mid-to-high 130s, recently changed 02s, bottom line is the Beast is running awesome. A few recent ad-hoc road races against E46 M3s are confirming that - pulls like a freight train.

I followed a boardmember's advice and went to an outfit called Turbotrix, was a little disappointed to find out I am there first M5 customer, but I figure a dyno is a dyno, right? These guys specialize in mostly Subies and Mitsus, have a four wheel dyno and many happy customers (they had a 800hp Evo on premises). My results were on a Dynojet (inertia dyno).

I followed David S.' diirections posted in a recent thread to a T. I personally pulled out fuses 17 and 30, DSC and ABS lights on. Had 2 fans cooling the engine bay, conditions are recorded in the attached data sheets (91 F, 12% humidity, 30 in-Hg pressure, 100ft or so above sea level). One thing I am not quite sure of is whether they had the Power button on, but from what I recall that gets diabled anyhow by pulling the above-mentioned fuses (right?)

All 4 pulls were done in fourth gear, makes me wonder whether 5th should have been used? Dyno operator's claim was they test all their 6-speed cars in 4th, but he had no good argument to my thoughts on that gearing ratios matter, not purely gear slot number. Anyhow, I am very surprised that with each consecutive run, the hp and tq figures were steadily increasing, resulting in a rather suspicous 15 hp difference between runs 1 and 4. Nevertheless the last run came to a meager 311 hp 297 tq. Turbotrix's explanation for this run over run improvement is the dyno is 'learning' more about the car. They claimed run 4 would be the most accurate as run 3 produced very similar numbers.

I also had them do an air-fuel measurement, I think that is pretty much in-line for the beast (high 11s to low 12s after 5500 rpm). The shop owner thought that was way rich. Also, I was dissapointed to see the results were summarized from 3000 rpm and up. Ultimately, the curve shape seems very much in line, except shifted down by at least or so 30 hp/tq!

Here are the results. Any thoughts on these out of whack stats?

TMontanaM5 · 10th July 2006, 01:51

Quote:

Originally Posted by cosioboy

OK, so I finally went to get a dyno measurement, but left severely dissapointed. I am pretty convinced the car is top notch, especially after the Powerchip 93 I got about a month ago, it has never felt stronger. I expected at least 340 atw factoring some of the mods, considering that is what most folks get on a pure stock Beast. My MAFS test is in the mid-to-high 130s, recently changed 02s, bottom line is the Beast is running awesome. A few recent ad-hoc road races against E46 M3s are confirming that - pulls like a freight train.

I followed a boardmember's advice and went to an outfit called Turbotrix, was a little disappointed to find out I am there first M5 customer, but I figure a dyno is a dyno, right? These guys specialize in mostly Subies and Mitsus, have a four wheel dyno and many happy customers (they had a 800hp Evo on premises). My results were on a Dynojet (inertia dyno).

I followed David S.' diirections posted in a recent thread to a T. I personally pulled out fuses 17 and 30, DSC and ABS lights on. Had 2 fans cooling the engine bay, conditions are recorded in the attached data sheets (91 F, 12% humidity, 30 in-Hg pressure, 100ft or so above sea level). One thing I am not quite sure of is whether they had the Power button on, but from what I recall that gets diabled anyhow by pulling the above-mentioned fuses (right?)

All 4 pulls were done in fourth gear, makes me wonder whether 5th should have been used? Dyno operator's claim was they test all their 6-speed cars in 4th, but he had no good argument to my thoughts on that gearing ratios matter, not purely gear slot number. Anyhow, I am very surprised that with each consecutive run, the hp and tq figures were steadily increasing, resulting in a rather suspicous 15 hp difference between runs 1 and 4. Nevertheless the last run came to a meager 311 hp 297 tq. Turbotrix's explanation for this run over run improvement is the dyno is 'learning' more about the car. They claimed run 4 would be the most accurate as run 3 produced very similar numbers.

I also had them do an air-fuel measurement, I think that is pretty much in-line for the beast (high 11s to low 12s after 5500 rpm). The shop owner thought that was way rich. Also, I was dissapointed to see the results were summarized from 3000 rpm and up. Ultimately, the curve shape seems very much in line, except shifted down by at least or so 30 hp/tq!

Here are the results. Any thoughts on these out of whack stats?

Change your Mass air sensors and pre cat O2 sensors which should resolve your problem. They should be replaced every ~40k miles anyhow.

mottati · 10th July 2006, 02:00

Could be related to temps. Despite correction factors, the car will produce less power on a warm day, especially one as sensitive as the M5.

The increase in power over the runs is likely caused by the drivetrain warming up, gearbox, diff and lubes getting up to temp.
Don't put too much weight on it.

Also, if you have 40k miles or more, new plugs, and probably mafs will get you another 15hp, i'd bet. I'm approacing 80k and plan on doing the pre cat 02 sensors when i get a chance, but they're supposed to be good to 100k.
Mike

BB6 · 10th July 2006, 02:32

I had a couple of observations regarding your dyno plots based on my experience (I have turbo Prelude that I tuned myself using Hondata S200b):

1. Dyno pulls should always be done on the highest gear before overdirve (i.e., 4th gear for a 5 speed, 5th gear for a 6 speed), so as to reduce drive train losses.
2. Your ambient temps were above 90 degrees. While you humidity didn't kill you, any time you tune in the heat, you will have lower readings. Do you have any IAT readings from the data log? If its anything above 110 degrees, you're losing power.
3. Where was the wideband O2 sensor? If you have a cat, and the sniffer is in the tail pipe, the O2 readings you've got really don't mean anything as the cat will skew the readings. For an NA car, I would keep the AF at low 13s, with the sensor placed 6-12 inches from the manifold. By any means though, high 11s/low 12s is waaayyy to rich for an NA car.
4. Did you check you plug gaps?
5. Is the computer pulling the timing?

Please post data logs if you can.

cosioboy · 10th July 2006, 04:25

Thanks for your thoughts, guys, but let me clarify: both precat O2 sensors changed wihin the last two months (felt an immediate improvement), my most recent MAFSs test yielded numbers in the high 130s (ltrs/hr), spark plugs changed as part of Inspection II late last fall, so based on the above I am pretty sure the culprits are not among MAFSs, O2 sensors, nor spark plugs.

As far as ambient conditions, while it was hot (91 degrees), humidity was low (12%) and even if one were to account for this, the correction factor is no more than a few horses.

As far as increase of power among runs: the car sat for no more than 20 minutes (under scortching sun) between the time I parked in front of the shop to the actual dyno test, so I don't think the car (and lubes) cooled down significantly, but I suppose it is plausible that accounted for the variantion in the dyno runs.

Gearing: what are the exact rations for the stock 3.15 diff - is indeed fourth gear the best, or is it in 5th gear that the ratio is closer to 1?

Air-Fuel ratio - any comments on that stat? I think my numbers are in line with what is expected in an M5, but the dyno shop recons they are way to rich for a NA car (as you too point out BB6)... As I mentioned, I got the Powerchip 93 a month ago, so it is possible they made the ratio too rich and I need to send it back for a proper re-flash.

One other thing - Sport button Off. I think (but am not sure) that this is disabled anyhow via taking out the fuses. Can someone confirm? Also, I think at WOT there is no difference, but again, need reconnfirmation on this.

Lastly, the data log. Didn't get anything other than the hard copy printouts as their computers were down, I've been promised to receive full date on Monday, will report back as far as the IAT reading.

Here are some pics:

gobuffs · 10th July 2006, 04:47

5th gear is 1:1.

I assume the same is true from an S14 to an S62....max power/safety is at an AFR is 12.5....anything leaner compromises safety margin.

cosioboy · 10th July 2006, 04:56

Quote:

Originally Posted by gobuffs

5th gear is 1:1.

I assume the same is true from an S14 to an S62....max power/safety is at an AFR is 12.5....anything leaner compromises safety margin.

Cheers for the reply, gobuffs. Do you think the fact that all runs were at 4th results in these way subpar figures, and if so, can I directly 'extrapolate' my results for 5th gear? Before I go back to the shop and demand a re-run, I want to make sure it is indeed an error on their part (it was their first M5 dyno test). Once again, the Beast runs amazingly well, I have no doubt in the car, and I am not convinced the 90 degree weather 'robbed' me a 30 to 40 horsepower, so I have to isolate it at this stage being a dyno/wrong gear issue.

I know for a fact that they didn't use the Power button, but not sure if that makes a difference (for one, it can be diabled via fuses 17 and 30, and two at WOT it may be no difference).

gobuffs · 10th July 2006, 05:08

I would figure the tranny gearing and the diff gearing would make a difference (and it seems like there are places in the dynojet software to put in these figures) but they never do so it leads me to believe it is irrelevant.

I can tell you from my experience in your shoes (lower figures than I expected but on an S14 not an S62- I am interested in doing the M5 but scared to in the same thought for the reasons you have shown) and chasing trying to figure out what it lead me to chase my tail for a long time and never fixed it. Learn this lesson.....Don't try to compare your numbers to what other people get on other dynos. You just can't compare. There are too many variables that are out of your control. The only way you are really going to know if there is something wrong is to run another car (that you know the power on) back to back with yours, ONLY then can you kinda somewhat maybe might able to make some sort of tiny inference about your car. If it feels good and it isn't going to blow up then....forgetaboutit.

mottati · 10th July 2006, 06:32

sport button is indeed disabled when you pull the fuses, and you are correct, at WOT, it makes no difference.

I still think the temps can make a difference. Sure, on a normal car, you could apply a correction factor, but when the M5 starts to heat soak, timing gets pulled back and the mixture goes rich, and you aren't going to correct for those issues with a correction factor. If you're really concerned, see if you can get an early am re-test for cooler ambient temps.

You were running 93 octane?
Mike

Evil One · 10th July 2006, 07:14

Gearing sure makes a difference, but the other way... 3rd gear will yeild higher numbers over a narrower speed range, as third is sending more torque to the wheels but at a lower speed, and torque is what a chassis dyno actually measures (actually on a dyno-dynamix it is the change in torque over time that gets measured)

However, Gobuffs is absolutely right... the chassis dyno is something that can only be compared to itself. Ie, if I do a run at shop A, and you do 1 using a similar machine at shop B, even if the temps and humidity are numerically the same we will get different readings for a myriad of reasons from the setup of the machine to the ramp rate the operator chooses to ....you name it

.
Similarly, if we both run on the same dyno with the same operator but on different days the runs are still not directly comparable.
Either you pull the motor out and use an engine dyno in a controlled enviro-room, or you use the ol' butt-dyno to do the absolute comparos.

In other words, don't worry if the numbers are numerically low as long as the car runs hard on the road and it feels like its pulling well.

Having said that, your AFR seems rich to me if its getting into the 11s. Yes, it is probably a very 'safe' tune, but that much fuel is surely robbing a bit of power. Checked the air-filters recently?

Cheers mate.