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Discussion Starter #1
Today I went to the dyno, 6 months after buying my 2000 M5:

312 HP, 306 Torque, 15.5 Air/Fuel ratio average

It's running quite lean, I would think it's due to the MAFS, since the car is really jumpy in the mornings, would that really rob 20HP?
 

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I just had my MY00 dynoed today, as well. The BMW club had a dyno day at RPM in Kirkland. After figuring out to pull fuses 17 & 30, I got 333 HP and 314 ft/lb, SAE adjusted. My car is stock w/ 36k. I am very impressed with the flat torque curve, over 300 ft/lb from 2,300 to 5,400 rpm! Horsepower peaked at about 6,700 rpm.
 

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amrit50 said:
Today I went to the dyno, 6 months after buying my 2000 M5:

312 HP, 306 Torque, 15.5 Air/Fuel ratio average

It's running quite lean, I would think it's due to the MAFS, since the car is really jumpy in the mornings, would that really rob 20HP?
That is VERY lean and cause for concern. Ideal A/F is near 12:1.
 

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About AFR: If they measured tailpipe AFR it is not the same as pre-cat AFR. The reason for this is the catalytic converter consume a lot of the free oxygene (what is actually measured by the AFR O2 sensors) when converting carbonmonooxide to carbondioxide and the NO to NO2.

AFR measured at the tailpipe will typically be about 1 unit higher than when measured properly, so I would assume your 15:1 actually is 14:1, which of course still is way too high.

Possible causes: contaminated MAFs, low fuel pressure, contaminated injectors.

Suggestions:

1. Perform MAF test

http://www.m5board.com/vbulletin/showthread.php?t=54788

2. clean MAFs

http://www.louv.tv/cars/m5/MAF/
(by m5board member Louv)

3. Do another MAF test

4. If not satisfactory, replace the MAFs

http://www.m5board.com/vbulletin/showthread.php?t=55391
(by m5board member Anzir)

5. Have fuel pressure measured

Measure the fuel-pressure both with and without the vacuum hose connected to the fuel-regulator. thsis should give fuel-pressures of 5.0 bar and 5.5 bar respectively. If the fuel-pressure is wrong you need a new fuel-pressure regulator, or a new fuel-pump. Possibly a new fuel-filter as well.

6. Run a bottle of Injector cleaner through the engine (for example STP Total System Cleaner)

David
 

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The dyno results are interesting. From this thread & others, it seems that there is a significant difference between a lot of dyno results (of stock cars) vs. manufacturer specs. Why is that?
 

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Discussion Starter #6
Thanks DavidS, I'm doing a MAF cleaning in the next 1-2 days, and i'll do some injectory cleaner, the car only has 52k on it, I don't know how dirty they could be...
 

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bksf said:
The dyno results are interesting. From this thread & others, it seems that there is a significant difference between a lot of dyno results (of stock cars) vs. manufacturer specs. Why is that?

Stock rates 394 and 368 that is at the crank...You'd have to remove the engine to compare...The dyno results you see are at the wheels, and the range is pretty steady at 330 to 340ish...
 

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Jayson said:
Stock rates 394 and 368 that is at the crank...You'd have to remove the engine to compare...The dyno results you see are at the wheels, and the range is pretty steady at 330 to 340ish...
True, but even that is a function of the particular dyno. I dyno'ed 323 with only Powerchip, so either my car was a low horsepower build car, or there is a fair amount of adjustment from dyno to dyno.
Regards,
Jerry
 

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gsfent said:
True, but even that is a function of the particular dyno. I dyno'ed 323 with only Powerchip, so either my car was a low horsepower build car, or there is a fair amount of adjustment from dyno to dyno.
Regards,
Jerry
Geez Jerry,

I hope that you/we do not have a low horsepower car...yourself, mottati, SACM5 and myself all have similar mods and we all dynoed within +/- 5 RWHP of each other...and on top of that, Mike has run over 160 L/H through his injectors...so hopefully, we all have "good" running engines...and to add more to the discussion, we all have different rear end ratios...

Mark
 

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gsfent said:
True, but even that is a function of the particular dyno. I dyno'ed 323 with only Powerchip, so either my car was a low horsepower build car, or there is a fair amount of adjustment from dyno to dyno.
Regards,
Jerry
There is a large difference between dyno's, not to mention air temps, fans differences all over the place, thats why you shoudn't live and die by the dyno, steve dinan went into huge depths about it, as have so many others.
 

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amrit50 said:
Thanks DavidS, I'm doing a MAF cleaning in the next 1-2 days, and i'll do some injectory cleaner, the car only has 52k on it, I don't know how dirty they could be...
MAFs seem to last only about 50-60k miles or so. Those are consumables on an M5...

As are fuel-regulators. Spend a few tens of dollars and have the fuel-pressure measured.

M5s have fuel pressure of 5.0 bar at idle and 5.5 bar at WOT. Most BMWs have about half of that. The regulators take a beating, I think.

David
 

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drallen said:
Geez Jerry,

I hope that you/we do not have a low horsepower car...yourself, mottati, SACM5 and myself all have similar mods and we all dynoed within +/- 5 RWHP of each other...and on top of that, Mike has run over 160 L/H through his injectors...so hopefully, we all have "good" running engines...and to add more to the discussion, we all have different rear end ratios...

Mark
Mark
I don't think I have a "slow" car, one of my mechanic/race buddies drove it and he thought it actually felt strong. And you are right, I know mottati and I had virtually the same post header dyno numbers, so I suspect we are all pretty close in power. Best MAF's L/H I have seen is 145 with AC on (if that makes a difference), I did another run and saw 141. Hot and humid in Florida so probably running a little less air. If mottati has complete exhaust that might account for some difference, as I am running stock exhaust except for Hamann mufflers.
Regards,
Jerry
 

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Jayson said:
There is a large difference between dyno's, not to mention air temps, fans differences all over the place, thats why you shoudn't live and die by the dyno, steve dinan went into huge depths about it, as have so many others.
I agree, dynos are best used for comparison of before and after mods, a lot harder to compare different cars.
Regards,
Jerry
 

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gsfent said:
Mark
I don't think I have a "slow" car, one of my mechanic/race buddies drove it and he thought it actually felt strong. And you are right, I know mottati and I had virtually the same post header dyno numbers, so I suspect we are all pretty close in power. Best MAF's L/H I have seen is 145 with AC on (if that makes a difference), I did another run and saw 141. Hot and humid in Florida so probably running a little less air. If mottati has complete exhaust that might account for some difference, as I am running stock exhaust except for Hamann mufflers.
Regards,
Jerry
Sorry Jerry,

I guess that my sarcasm did not come through my post... :)

I think that we all have "normal" or "strong" motors...because we all posted similar RWHP numbers...

Regards,

Mark
 

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Ag Surfer said:
That is VERY lean and cause for concern. Ideal A/F is near 12:1.
On a NA engine, 12:1 is fat. Best power, economy, safety can be achieved near 13.5:1 NA. If it was FI, 11.5-12:1 is ideal.

--wes
 

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wesmanz said:
On a NA engine, 12:1 is fat. Best power, economy, safety can be achieved near 13.5:1 NA. If it was FI, 11.5-12:1 is ideal.

--wes
Near redline and WOT, most tuners like to see low 12's on the AFR. At cruise, 14.7 is most economical. Most readings are in the 14's and go down to 12's. I agree, FI needs a little more fuel because FI effectively raises the CR. Also, list wisdom seems to be that tailpipe sniffers used for AFR are about a point higher than what you might see precat.
Regards,
Jerry
 
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