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

[Mihnea Cotet]

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