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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Understanding 335i Dyno results and Correction Factors (300+hp@whlz stock!??)



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      06-03-2007, 09:30 AM   #1
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Understanding 335i Dyno results and Correction Factors(SAE, STD, UNCORRECTED)

Next time someone shows you a 335i dyno graph, make sure you know all the variables involved, before you use that as the sole reason for justifing a purchase. The combination of a turbo car, a smart ECU, assumptions of the dyno software, and a little bit of ignorance can lead to some very large, and very FALSE 335i dyno numbers!

Consider this a public service annoucement, with the proof to back it up.

I noticed that lots of people around here love to brag about high stock dyno numbers, and then I look at their graph and see something that makes me lose all trust in it... here is an example.

this is my ACTUAL 335i dyno, STOCK, as given to me by the dyno shop

CHECK IT OUT GUYS... I HAVE THE FASTEST STOCK 335 IN THE WORLD!! (or so it seems)

Anyone who can look at the graph, and tell me why its probably false, and cant be trusted is already a step ahead. Good job.

The answer? SAE correction. (or STD correction, which is just slightly different, but still designed for a normally aspirated engine)
Now thats not saying all graphs with SAE/STD are false... no.. just the ones on a 335i turbo engine with a stock ECU that already compensates, and then with a CF over 1.0 are actually inflated. Piggybacks included... because these still use the stock ecu for adaptation and correction.

CF is not entered by the operator, it is calculated based on enviroment variables... STD and SAE are different ways of calculating the CF.

Its amazing how many people are confused on this...

Here is how CF is calculated with the SAE calculation...


Pd = the pressure of the dry air, mb
Tc = ambient temperature, deg C

cf = the dyno correction factor end result (THIS IS A RESULT, NOT AN INPUT, AND IS NOT SHOWN ON THE PRINTOUT BY DEFAULT!!)

The horsepower and torque available from a normally aspirated internal combustion engine are dependent upon the density of the air... higher density means more oxygen molecules and more power... lower density means less oxygen and less power. Our turbo car already compensates by running the turbos harder, to create the same ABSOLUTE pressure... meaning that we dont lose *all* this power like a normally aspirated engine does, and the calculations dont work for us!

The relative horsepower, and the dyno correction factor, allow mathematical calculation of the affects of air density on the wide-open-throttle horsepower and torque. The dyno correction factor is simply the mathematical reciprocal of the relative horsepower value.

Unlike most cars that would lose significant HP and TQ under extreme conditions, the 335 ecu automatically adapts to keep power output close to stock levels, even when the enviroment variables SUCK(hot air, high humitidy and altitude).

That means that the dyno software doesnt need to calculate it... our cars are doing most of it for us! And these graphs prove it.

How does it do that?

well... its complicated, but its my understanding that basically it uses the T-MAP and Baro sensors to sense pressure and Tempurature, and then keeps final boost pressure, and also fuel and timing in check with the closed loop wideband o2 system that constantly monitors AFR, and adjusts fuel, timing, and boost in realtime to acheive the same final power output under varrying conditions.

Here is my STOCK dyno graph. This is how it was handed to me after the runs, and the whole shop about pissed their pants. Dont get all exited about the numbers, as you can see, they are SAE corrected.



392hp at the wheels??? you gotta be crazy to beleive that!

So we switched to STD correction (which shiv@vishnu ussually prefers because its closest to 1.0 at his shop)



Ok, thats still way too high... lets turn off ALL correction. A CF factor of 1.0 Just the RAW numbers that the dyno read.



Wow, those numbers look exactly like where a stock 335 should dyno at! Its hot, humid, crappy weather, and an UNCORRECTED dyno is the most accurate as to what it should be.

What does this mean?

Well, for me personally, it means that I will NEVER trust a 335i dyno graph with anything that isnt close to a 1.0 Correction Factor... because thats the actually power output. Never beleive a corrected 335i dyno graph, unless they show you the correction factor.

Anything else is just inflated or deflated because of 2 correction systems (the one in the 335, and the one in the dyno software) working with eachother doing the same thing, and making false numbers.

Those of you getting your 335i's dyno'd should request dyno graphs that are uncorrected, so you can see the real numbers that the car put down.

Below are the conditions during the dyno runs... these line up with the runs above. they were 10 seconds apart, notice how each run gets hotter(it was a small room), yet the 335 did not lose power! (it actually gained power as it got heatsoaked!) That is the 335i adaptation and realtime enviromental correction in action.

You can also see how on the SAE graph, as the TEMP got hotter, it applied MORE correction, and therefor the hotter run showed even MORE power... since the ECU already adapted for the hot air.

We have a very smart car on our hands, and this is a testiment to how well a device like turbo tuner, or something as simple as the "terry tuner", or better yet a PROcede/Xede system will work to raise power output... a little fooling of the ECU, and you just gained a ton of power that was already in the "reserves".
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      06-03-2007, 09:36 AM   #2
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I imagine some poor dude before you who thought he gained 50hp (because of the CF factor) after he put in an exhaust system or intake...or even worse the turbonator.
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      06-03-2007, 10:15 AM   #3
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good post.
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      06-03-2007, 10:20 AM   #4
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Awesome post
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      06-03-2007, 10:20 AM   #5
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Any other examples of someone posting a dyno graph that was inaccurate due to a CF?
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      06-03-2007, 10:42 AM   #6
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Quote:
Originally Posted by Str8EJ View Post
good post.
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Originally Posted by ArmyBimmerDude View Post
Awesome post
Thanks...

Maybe we can get this post stickied, since it gets discussed so much, and this finally proves it.
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      06-03-2007, 10:43 AM   #7
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Two things about dynos:

1. They are good as a before and after tool. Basically, dyno the car, do a mod and then dyno again and look @ the delta, ie, change in the area under the curve.

2. Use correction factors only when comparing dyno numbers that are done @ two different time periods on the same dyno. Correction factors keep temp/baro/humidity variables constant so the numbers become more meaningful. Use uncorrected numbers when you do one dyno session.
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      06-03-2007, 10:53 AM   #8
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Quote:
Originally Posted by nj1266 View Post
Two things about dynos:

1. They are good as a before and after tool. Basically, dyno the car, do a mod and then dyno again and look @ the delta, ie, change in the area under the curve.

2. Use correction factors only when comparing dyno numbers that are done @ two different time periods on the same dyno. Correction factors keep temp/baro/humidity variables constant so the numbers become more meaningful. Use uncorrected numbers when you do one dyno session.
I agree with #1, but I disagree with #2 to a point. Yes that works with most cars, but with cars that already compensate for temp/baro/humidity by adding more boost/fuel, like the 335 does, then any correction yeilds info that would be true on most cars, but false for the 335. Thats the whole point of my post... correction factors dont show true info on a car that already has its own correction.

Look at the 3 runs on the SAE graph in my original post, and then look at the tempurature for those runs. SAE correction makes the hotter runs have MORE power, because SAE assumes that hotter runs theoretically have less power on the UNCORRECTED graph, but it doesnt, it has the same, or even more power, because the 335 ECU corrected for the TEMP.

If my first run was 85 degrees, and my last run 100 degrees, then SAE would show the 100 degree run as having alot more power, and the uncorrected graphs would show power that is the same regardless of temp... because the 335 ecu compensates
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      06-03-2007, 10:56 AM   #9
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Great post.
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      06-03-2007, 10:56 AM   #10
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Great post and solid work, I wish everyone put that level of work into these types of posts.
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      06-03-2007, 11:03 AM   #11
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Good post. There was another guy awhile back that dyno'd stock at couple 1000 feet elevation and came out with near 300 at the wheels and claimed it was correct. But again, the correction factor combined with the ECUs ability to correct made the numbers inflated...not as inflated as yours, but same premise.
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      06-03-2007, 11:08 AM   #12
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Quote:
Originally Posted by catm3 View Post
Good post. There was another guy awhile back that dyno'd stock at couple 1000 feet elevation and came out with near 300 at the wheels and claimed it was correct. But again, the correction factor combined with the ECUs ability to correct made the numbers inflated...not as inflated as yours, but same premise.

I remember that...
He even put his numbers in his sig, bragging about his SAE corrected numbers.
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      06-03-2007, 12:50 PM   #13
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The shop that I always use to use back home in NY for my turbo S2K had a dynojet, and they would always use a STD CF of 1.0. I always assumed that it was normal, but I didn't care much because it was always consistent so I could see if I was actually gaining power with other mods, and NA S2K's would always put down 200whp so I thought it was a well accepted CF.
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      06-03-2007, 12:50 PM   #14
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Good story about dyno readings:

http://www.sportcompactcarweb.com/ed..._technobabble/
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      06-03-2007, 03:37 PM   #15
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Quote:
Originally Posted by BoostedBMW View Post
The shop that I always use to use back home in NY for my turbo S2K had a dynojet, and they would always use a STD CF of 1.0. I always assumed that it was normal, but I didn't care much because it was always consistent so I could see if I was actually gaining power with other mods, and NA S2K's would always put down 200whp so I thought it was a well accepted CF.
STD at 1.0 is the same as uncorrected. This isnt something that they change, this number is what the computer calculates based on conditions, and STD or SAE are the algorithms used to get that number, which is essentially a percentage. 1.1=110%

Also, on a NA s2k, the correction factors are more acccurate, it actually does lose power with high temp and high altitude. the 335 on the other hand does not lose as much.(the ecu compensates)

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      06-03-2007, 10:09 PM   #16
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Quote:
Originally Posted by matsarge View Post
Great post and solid work, I wish everyone put that level of work into these types of posts.
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      06-03-2007, 11:34 PM   #17
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Quote:
Originally Posted by RiXst3r View Post

Also, on a NA s2k, the correction factors are more acccurate, it actually does lose power with high temp and high altitude. the 335 on the other hand does not.(the ecu compensates)
Wouldn't be so sure of that. Have you run a vehicle at high altitude? I've been anywhere from sea level to 12,000 feet. The 335i ECU cannot perform magic. There is definitely power loss at altitude. Perhaps not as bad as N/A, but there is definitely a loss.
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      06-03-2007, 11:38 PM   #18
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Quote:
Originally Posted by leftcoastman View Post
Wouldn't be so sure of that. Have you run a vehicle at high altitude? I've been anywhere from sea level to 12,000 feet. The 335i ECU cannot perform magic. There is definitely power loss at altitude. Perhaps not as bad as N/A, but there is definitely a loss.
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      06-04-2007, 06:14 AM   #19
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Quote:
Originally Posted by leftcoastman View Post
Wouldn't be so sure of that. Have you run a vehicle at high altitude? I've been anywhere from sea level to 12,000 feet. The 335i ECU cannot perform magic. There is definitely power loss at altitude. Perhaps not as bad as N/A, but there is definitely a loss.
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Originally Posted by Terry335 View Post
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ok... yes, there is SOME... but thats not the point. The point is that there is no where near as much loss as SAE correction assumes.

proCede/Xede guys will see more of a loss than stock guys, because the turbos cant keep up. The more power you take away from the "reserves" the more you lose when you need to tap into them.

leftcoastman... remember your dyno at high altitude? You said you posted the RAW numbers

Quote:
Originally Posted by leftcoastman View Post
Everyone was surprised at the very minimal (if any) reduction in power and I was shocked at the torque numbers. Keep in mind the values I posted are from a Dyno Dynamics that reads 13% lower than a Dynojet!

268whp @ 5250 rpm/ 316wtq @ 2800 rpm

Also... Remember the high altitude track results where stock and procede/xede 335's where extremely close in performance? The gap is ussually much larger at low altitude tracks. Maybe that was because of other factors... but still, you cant rule out the fact that the turbos might have been maxed out on the tuned cars (i remember hearing about a lot of CEL's too)

Of course there is SOME loss, but my point was that its no where near the loss that is calculated in SAE correction factors!

terry: when are you going to dyno your "terry tuner"?

Last edited by RiXst3r; 06-04-2007 at 06:57 AM.
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      06-04-2007, 10:19 AM   #20
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Great post! Thanks for putting it together.
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      06-04-2007, 11:11 AM   #21
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Quote:
Originally Posted by RiXst3r View Post
Also... Remember the high altitude track results where stock and procede/xede 335's where extremely close in performance? The gap is ussually much larger at low altitude tracks. Maybe that was because of other factors... but still, you cant rule out the fact that the turbos might have been maxed out on the tuned cars (i remember hearing about a lot of CEL's too)

Of course there is SOME loss, but my point was that its no where near the loss that is calculated in SAE correction factors!

terry: when are you going to dyno your "terry tuner"?
I'd agree that the higher boost cars are running out of compressor at higher elevations, but even the fastest stock car was running slower than stock cars run at sea level. The ECU raises boost to try to compensate, but itís not 100%.

On the Terry Tuner, I might go this week. I'm not a huge fan of going to the dyno because it's a little expensive and I'd rather spend the time going to the track, but I'll bite the bullet for the betterment of e90forum.
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      06-05-2007, 07:01 AM   #22
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Quote:
Originally Posted by Terry335 View Post
I'd agree that the higher boost cars are running out of compressor at higher elevations, but even the fastest stock car was running slower than stock cars run at sea level. The ECU raises boost to try to compensate, but itís not 100%.

On the Terry Tuner, I might go this week. I'm not a huge fan of going to the dyno because it's a little expensive and I'd rather spend the time going to the track, but I'll bite the bullet for the betterment of e90forum.
just make sure you get one with uncorrected numbers
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