since cold air is denser then hot air, when you dyno and its cold outside and say you have 14 a/f ratio at x rpm and then dyno again when its hotter would the a/f go down to say 13 at the same rpm given same conditions(besides temp)? how does this work or does it stay the same? it doesn't seem like it would stay the same but i don't know.

 

Yes it will change, but to my understanding it will not be one full point it would be something like 0.2 or maybe less.

Az

 

the ratio should stay the same because your air flow sensor compensates for the amount (mass maybe?) of air going into your cylinders. the total amount of air will be less (thus less potential combustion energy inside the cylinder and thus less power) since it's less dense but the ratio to fuel better be somewhat constant. but i'm also not an expert.

 

Some tweeking is ideal as environmental conditions change. Aside from temperature, barametric pressure and humidity come to mind as influencing combustion.

Our Mass Air Flow (MAF) sensors use a "hot wire" to make measurements. Basically an electric circuit tries to keep a wire in the middle of the intake at a constant temperature. As air flows over it and cools it off, the circuit has to work harder to heat it back to the right temperature. The air flow is determined by how hard the circuit has to work to keep the wire hot.

I believe there is also a thermometer in the air flow that is used to correct the reported flow rate. I presume that auto manufacturers have found this to be sufficient for reliable combustion. Otherwise, we'd have barametric pressure measurements as well as humidity sensors.

As for aftermarket tuning, I wouldn't necessarily count on your car being perfectly tuned for all environmental conditions. I guess it really depends on how the tuning is implemented (piggyback, modified fuel/timing maps, new ecu?).

--
Jeff

 

thanks for the replies

 

1% per 11F change is the density correction factor, so at 30F vs 70F expect a ~~4% power gain at the same barometric pressure.
Corrected for tire friction to road/dyno roller losses [so ~~3.5%]

Acceleration is a cube root function [approximation] so 10% more power yields ~~ 2.15% faster ET.

Once intake air is above 90F you enter summer protective mode program which limits power as temp rises.