[ba] Re: [s-cars] 80tq: 20v Project Update, 415whp, 12.25, etc

Brett Dikeman brett at cloud9.net
Thu Nov 11 20:41:52 EST 2004

At 10:35 AM -0500 11/11/04, JShadzi at aol.com wrote:

>  but I will say that it is commonly accepted that "SAE Corrected" 
>dyno figures are notoriously inflated for boosted turbo motors at 
>   The higher you get, the more boost you run, the more inflated they are.

SAE corrections are wrong for forced induction engines, but not for 
the reason you give.

Absolute manifold pressure on a forced induction engine is NEVER 
altitude corrected, and I'm not aware of ANY ecu that uses relative 
manifold air pressure; there's simply no point.  Even turbo airplanes 
use absolute MAP gauges.  The only use for an altitude sensor on Audi 
ECUs is for preventing overspun turbos at altitude...

SAE correction corrects for air density, to put normally aspirated 
engines on a common playing field.  Most of the factors (which all 
affect NA engines) that go into calculating the correction, do not 
apply to turbo engines.  They are temperature, barometric pressure, 
and humidity.

>I believe you when you say your car feels faster at lower elevation, 
>my assertion is that the "corrected" dyno figures at elevation are 
>inflated and not accurate for heavily boosted motors.

Any forced induction engine that has been dyno'd and "SAE corrected" 
was dyno'd by someone who had absolutely no idea what they were 
doing, or intentionally used the correction to make for a happy 

   Customers don't like seeing that an air filter or exhaust or cam 
only added 2-3hp, or more frequently the customer wants to "test" 
their performance wares, so shops do any of a number of things to 
make people leave happy:

-locate the dyno's ambient air temperature sensor somewhere very hot 
compared to what the engine is drawing in.  Behind the dyno's console 
PC.  Above a light fixture.  Way up at the top of the garage/ceiling. 
In the sun.  Etc.  One Australian dyno operator was caught by 
Autospeed HOLDING the temperature sensor to raise the temps 20+ 
degrees and grossly inflate figures post-correction.
-set the barometric pressure too low, if the dyno does not have a 
barometric sensor builtin
-enter too high a humidity, again if the dyno does not have a sensor for it
-run the dyno run with cold coolant instead of with the engine at 
operating temperature
-use a grossly inflated transmission loss correction
-use different gears for the before+after

That's most of them.  That's why a scam artist can make a tin foil 
widget you stick in your intake, run the car on a dyno for cameras 
for their infomercial, and demonstrate power increases with it 

"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin

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