Air density correction factor vs power.

[Stkid93]

Hey guys,

I have recently been studying a lot about air density correction factor. This is something that is used on the focus st platform a ton, but hasn’t made its way to the fist as much. So I figured I would post about it for those who don’t know about this.

there is a gauge on the accessport called air density corr. This reading is typically anywhere from .85-1.2. The idea is very similar to DA in drag racing.

1.0 reading signifies an absolutely average day in terms of potential power. Anything above 1.0 means it’s a good environment for making power. While anything under 1.0 means it’s bad environment for making power, this could be because of the following factors

- altitude
- temp/air intake temps
-humidity
-location of air intake/efficiency of intercooler

If you are consistently seeing under 1.0, there are some ways to help. The biggest way would be meth injection. Spraying a water/meth mixture can cool down the air and help counteract a bad air density reading.

in fact there is a tuning shop called banks tuning or something like that, and he has done a ton of testing on air density. And he went on pikes peak, reaching a maximum altitude of 11,000 feet. And by using meth injection, he was able to make the same power at 5k feet and 11k feet despite the drop in air density.

he also put on a data logger and showed it as he drove up in altitude and the air density went down as low as .8 at 5000 feet elevation. This changed the potential horsepower output of his engine over 100 horsepower according to his data.

 

[agangel]

The tune on my car is variable based on barometric pressure so I can do mountain runs. This gauge may be useful for me. Thanks.

 

[NATYPE]

Sweet! Definitely going to watch that gauge for a bit day to day now just to see how it responds. I'm really impressed with temps (comparing charge and ambient) in any meaningful scenario (anything but completely still) with a giant pod filter and oversized intercooler. I wonder if I'll spot any negatively leaning readings anywhere noteworthy.

 

[agangel]

Day to day at static elevation probably very little variance. I'm going to watch it next time I climb altitude and see what happens though.

 

[Intuit]

water/meth mixture can cool down

Since water can't be compressed and isn't broken down during the combustion process it also occupies unrecoverable space in the cylinder. Seems somewhat like increasing the compression ratio... minus some of the negatives like increasing potential for knock.

 

[Dialcaliper]

Since water can't be compressed and isn't broken down during the combustion process it also occupies unrecoverable space in the cylinder. Seems somewhat like increasing the compression ratio... minus some of the negatives like increasing potential for knock.

Not really true. With the amount of water used in a properly tuned water-meth system, Just the compression stroke and residual heat from the hot piston and head is enough to vaporize the water if it’s properly atomized going into the cylinder. The anti-knock properties of water are mainly due to the steam’s higher capacity to absorb heat and convert that to pressure. Basically you get lower temperature and higher pressure in the cylinder, which is a very good thing. When water injection taken to the absolute extreme (like in WW2 aircraft), adding water as much as 30-50% of fuel injection, because on top of the knock resistance, you’re effectively also getting quite a bit of extra power because the engine is now partially acting like an old-timey steam engine, not just as a classic “internal combustion” engine.

Pure water injection is a thing, not just water/meth. Adding methanol is more common than straight water because it’s also basically adding more fuel. Also methanol also keeps “biological” things from growing in your supply tank and clogging your injector(s).

Methanol, ethanol and gasoline (aka rich fuel mixtures) do a bit of something similar, just not as well as water. Methanol and ethanol also have a lot of other stuff going on, like higher octane/knock resistance, and that you get extra oxygen in the cylinder that’s attached to the fuel.

If you actually have liquid water in the cylinder (as opposed to atomized droplets or steam), you’ve got a big big problem.

 

[M-Sport fan]

^^^How did those WW2 fighter planes keep said water tanks for water injection purposes from freezing at the higher altitudes, tank heaters?

 

[Dialcaliper]

^^^How did those WW2 fighter planes keep said water tanks for water injection purposes from freezing at the higher altitudes, tank heaters?

Sorry, wasn’t clear - warplanes used Water/Meth and its not just the tanks that needed to be kept warm. Releasing straight water into high altitude, very cold air would probably produce ice crystals going into the cylinder ports 🤯

Some other applications do use straight water, but as you’ve surmised, mixing in methanol has other advantages

 

[Intuit]

Not really true. With the amount of water used in a properly tuned water-meth system, Just the compression stroke and residual heat from the hot piston and head is enough to vaporize the water if it’s properly atomized going into the cylinder. The anti-knock properties of water are mainly due to the steam’s higher capacity to absorb heat and convert that to pressure. Basically you get lower temperature and higher pressure in the cylinder, which is a very good thing. When water injection taken to the absolute extreme (like in WW2 aircraft), adding water as much as 30-50% of fuel injection, because on top of the knock resistance, you’re effectively also getting quite a bit of extra power because the engine is now partially acting like an old-timey steam engine, not just as a classic “internal combustion” engine.

Pure water injection is a thing, not just water/meth. Adding methanol is more common than straight water because it’s also basically adding more fuel. Also methanol also keeps “biological” things from growing in your supply tank and clogging your injector(s).

Methanol, ethanol and gasoline (aka rich fuel mixtures) do a bit of something similar, just not as well as water. Methanol and ethanol also have a lot of other stuff going on, like higher octane/knock resistance, and that you get extra oxygen in the cylinder that’s attached to the fuel.

If you actually have liquid water in the cylinder (as opposed to atomized droplets or steam), you’ve got a big big problem.

It occupies space but is relatively inert and doesn't break down, react or serve as fuel for the combustion process. The H₂O that enters the cylinder is still leaving the cylinder as H₂O.