[s-cars] Re: From the Horses Mouth at DynoJet (SAE)

[QSHIPQ at aol.com]

What everyone should consider is that if you really want to compare your performance to anothers, do a dyno day.  The problem I see in a turbo application is, you tune for different goals at altitude and sea level.

The FMIC is the first big spot.  At altitude most turbos will work harder to get the same number it would at sea level.  That creates more heat, so it could be key to have an FMIC at 5000 ft, and not so key to have one at altitude.  Bring the big FMIC tuned at altitude down to sea level, you can make the motor experience turbo choking.  You could also find a whole lot of surging because it's quite possible you will find the WG valve isn't big enough.  

The question really is can we compare altitude results with sea level results.  I don't think it's a "somewhere in between CF" at all.  I think it's misinformed people trying to compare apples to oranges. Apples to apples on a small displacement motor just can't be optimized or virtually compared for two radiaclly different altitudes.  If somewhere in between means identifying a "local correction factor" that sounds reasonable.  However, the accepted baseline should still be conditions of test and uncorrected figures.  Certainly for tuning, I'd use uncorrected to no-nuttin (tm - dahkine Hap uses).

S990mbJ


In a message dated 11/16/2004 1:15:09 PM Eastern Standard Time, Mihnea Cotet <mihnea.cotet at easynet.be> writes:

>Cody, interesting statement from the horse's mouth indeed.
>
>Would this make all CO S-car owners reconsider their HP #s?
>
>Is this totally true?
>
>Does a car in CO only produce uncorrected HP at altitude?
>The biggest problem is that measuring power at sea level and comparing it 
>to uncorrected power at altitude isn't going to make anything better, 
>because the measurement conditions are different, i.e. different ambient 
>pressure.
>
>Depending on a lot of variables (like altitude correction for boost being 
>still on or off in the ECU), this can totally change the power the car is 
>putting out.
>
>In a normal case, where altitude correction is on a chip programmed to run 
>2.5 Bar (for instance) absolute pressure at 4k RPM is going to be 1.5 Bar 
>boost+1Bar ambient pressure at sea level and 1.5 Bar boost+0.8 Bar ambient 
>pressure at altitude because of the altitude correction that won't let the 
>turbo run 2.5 Bar absolute pressure but rather 2.3 because of the altitude 
>correction.
>
>This means the PR at the compressor outlet is around 2.6 at sea level and 
>2.4 at altitude. Less pressure means lower shaft speeds, more thermal 
>efficiency and less air flow also.
>
>In your case, where the altitude correction is off (I have turned it off, 
>MTM even turn it off in the 1+, which I don't do for my "stage 1" chips), 
>your chip is programmed to run 2.8 bar absolute at 4k RPM. 2.8 at sea level 
>is 1.8 bar boost, in CO it's 2.0 Bar boost or 28 psi. Thus the turbo is 
>working harder and probably less efficiently...not a big deal with your 
>FMIC (god I love your FMIC, your intake temps are soooo cool :-)) ) but 
>could be a big deal for someone else...
>
>
>All this is pretty puzzling, I don't know what conclusion to draw. I 
>personally wouldn't just say "a turbo car runs uncorrected power at 
>altitude".... as you said on AW, the truth lies somewhere in between :-))))
>
>
>My 0.02 Euros (currently worth a lot more than 0.02 USD),
>
>
>Mihnea
>
>www.mrc-developments.com
>
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