Author Topic: Dyno Questions  (Read 1696 times)

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Eric

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Dyno Questions
« on: March 24, 2005, 06:04:19 PM »
Ok, to start off i dynoed my car twice, once at MAC, and again at Redline.  The first time at MAC i had an intake and REVO on my 1.8t GTI. I dynoed 214whp, and 275wtq. Now this is with the 1.23 SAE correction factor. (that is normal correction factor that MAC uses) Next was Redline, and i added a TB exhaust. I did 204whp and 269wtq with a 1.14-1.16 correction factor. (i forgot the exact number) on both of the runs i had a bunch of CEL's, so that might have hindered performance. Now here are the questions:
1. should there be a correction factor at all for turbocharged cars up at altitude?
2. If yes, what should it be on the average?
3. Which numbers should i say i did?

Thanks guys, this was on my mind for awhile, and i finnaly posted about it.



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DenverPat

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« Reply #1 on: March 24, 2005, 07:05:40 PM »
The correction factor is the same for forced induction and n/a cars.
Dynos are all relative.  Big differences between them.  I'd take all numbers with a grain of salt.  I like to use them for a/f readings and to see the power curve.
So at MAC, all you had was a chip and intake?  Those are some damn good  numbers.  I'm not sure I'm getting all I can out of my quattro A4, but my numbers were 245hp/295tq.  Granted, those were at the flywheel.  I may be getting revised software soon, so that may make a difference.
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« Reply #1 on: March 24, 2005, 07:05:40 PM »

JDawg

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« Reply #2 on: March 25, 2005, 03:00:14 AM »
The correction factor should be based on a number of things, and that number should change depending on the following.

Current atmospheric air density
Current due point / relative humidity
Exact altitude
Ambient air temperature
Barometric pressure

Those factors are what make up the SAE correction factor (standardized method for calculations, in this case a correction factor) Honestly, I would expect that assuming the air temperature was around 45 degrees, the pressure was normal, the altitude was around 5280 feet, the humidity was about 25% the correction factor should be about 1.18 - 1.19 or so.  1.23 seems high to me, but again that depends on what the conditions were like at MAC at the exact time your dyno was taken.  In theory, the two dyno's should equal out to be the same on a car that was run at both locations, even if the conditions changed as long as the correction factor is correct.  

Make sense?  In other words, there is no way for anyone to tell you if the numbers are right unless you have information about the conditions at the time your dyno was completed.
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DenverPat

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« Reply #3 on: March 25, 2005, 04:11:16 AM »
IMO, more than likely the difference is attributable to differen dynos as opposed to differing environments.  Dynos differ greatly between models.
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Eric

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« Reply #4 on: March 25, 2005, 04:21:31 AM »
i understand what you guys are saying, but i was under the impression that the correction factor for a turbo-charged car would be signifigantly less than that for a NA car. Also for the MAC one, i actuallly callculated what the right correction factor should have been, and it should have been 1.19, and it was 1.23......and i have heard that they bump up their numbers. (not dissing at all, i really like them over there) so i dunno what to think



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JDawg

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« Reply #5 on: March 25, 2005, 04:27:31 AM »
I have nearly no knowledge about what the differences between models of Dynos are, but I too have heard that they very greatly.  For the most part, I think shops sometimes use the correction factor to make your car look a little better, and in your case that may be what happened.  1.19 Or 19% sounds about right for Colorado in general.  If you want to know what your car's computer thinks the correction factor is, you can look at measuring block 66 (I think) on a VAG, and it will show the percent that the ECU is adjusting for.  Mine says 17 right now.  

As far as the difference between NA and Turbo, there should not be any at all.  The correction factor is simply a calculation to find the absolute air density.  NA and Turbos have the same amount of air available to them, but a Turbo can force more of it into the engine, resulting in higher than ambient internal intake pressures.  That is the only difference.  The Dyno doesn't care.
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gragravar

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« Reply #6 on: March 25, 2005, 01:08:22 PM »
So I see what you guys are saying, and I don't doubt that you are correct about the correction factor not differeing for turbo cars.  BUT, logically I have to agree with eric that there should be a difference.  If the correction factor is to correct for altitude/temp/etc in order to provide a read of what your car will do at sea level, then using the same factor artificially inflates the reading for turbo cars.  As turbo cars force in addtional air up to a certain level, then adding more ambient air will not impact the output of power as the total air in the comubstion chamber will not substantially change.   at altitude we just work the turbos harder.
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DenverPat

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« Reply #7 on: March 25, 2005, 01:09:26 PM »
Quote from: "JDawg"
As far as the difference between NA and Turbo, there should not be any at all.  The correction factor is simply a calculation to find the absolute air density.  NA and Turbos have the same amount of air available to them, but a Turbo can force more of it into the engine, resulting in higher than ambient internal intake pressures.  That is the only difference.  The Dyno doesn't care.


Very well said, Jason.
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jfrahm

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« Reply #8 on: March 25, 2005, 01:44:14 PM »
It depends on the turbo setup.  My Passat seems to boost to a certain absolute pressure, I see 10 psi on my guage but if you work out the math guage pressure plus local barometic pressure roughly equals the 8psi of boost the Passat gets at sea level.   Now if you have an MBC sensing only the relative pressure between the manifold and the wastegate you'd get the same boost here or at sea level but at a lower starting point here.  The tricky part is that with an MBC you can probably get away with 2psi more boost here than you could at sea level, your correction factor on the dyno might correct you to HP you cannot make due to knock or limitations of your fuel system or something.

If you have tuned for the max safe boost here I do not think you can use much of a correction factor, if any.

-Joel.
2001 Audi A8 Quattro 4.2l

JDawg

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« Reply #9 on: March 25, 2005, 01:56:56 PM »
Check http://wahiduddin.net/calc/calc_da.htm for more information on Density Altitude.
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Eric

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« Reply #10 on: March 25, 2005, 02:03:44 PM »
Quote from: "JDawg"
Check http://wahiduddin.net/calc/calc_da.htm for more information on Density Altitude.


Thats what I used to calculate my dyno chart from MAC. I calculated a 1.19.....(for NA cars IMO) and it used a 1.23SAE correction factor for my car. So either they bumped it up to 1.23 or the dyno made a mistake.


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jfrahm

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« Reply #11 on: March 26, 2005, 02:19:26 PM »
Again with a turbo car it's the absolute pressure inside your manifold that matters, not the pressure outside, or the relative pressure (mechanical boost gauge reading.)  At least as far as HP on boost is concerned.  Correction factors are for NA cars or low tech tubo systems, or for inflating HP numbers to pump up dyno customers.

If you are running an MBC _and_ you have not already dialed in more boost to make up for the lower air density for our altitude you can use a correction factor.  As I recall the rule of thumb is about 1/2 what is used for NA cars.  However most people with an MBC have already turned it up to compensate for altitude, and would need to dial boost back a couple PSI if they went to sea level.  Then they'd have about the same amount of air and fuel in the combustion chamber there as they would here.

Remember do not think in terms of boost on a turbo car, think in terms of absolute pressure and the number of air molecules in the combustion chamber.

-Joel.
2001 Audi A8 Quattro 4.2l

Eric

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« Reply #12 on: March 26, 2005, 02:26:51 PM »
Quote from: "jfrahm"
Correction factors are for NA cars or low tech tubo systems, or for inflating HP numbers to pump up dyno customers.



ok cool, thats what i thought. so now i need to figure out what my real numbers are....... :D



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