Dumb Question

[sickr33]

couldn't agree more volume of air and fuel make power

a big turbo @ 10psi will make more power the a small turbo @ 20psi

psi don't mean shit its the volume/mass/amount (what ever you want to call it)

of oxygen that counts

hence you make more power on a cold damp night than you would on a hot dry day because the air is denser (more partials of oxygen in the same volume of air)

[Thelen]

couldn't agree more volume of air and fuel make power

a big turbo @ 10psi will make more power the a small turbo @ 20psi

psi don't mean shit its the volume/mass/amount (what ever you want to call it)

of oxygen that counts

hence you make more power on a cold damp night than you would on a hot dry day because the air is denser (more partials of oxygen in the same volume of air)

Well, you'd have to look at the compressor map of those turbos, because even a turbo 50% bigger wouldn't make the same air flow if it is at half the boost, but generally you are right, it comes down to air flow.

The temperature of the air is a very interesting factor, because most engines measure it BEFORE the intercooler and turbo, so it does assume certain variables after that fact. The AFM measures flow X temperature X pressure all at once, and changing any of those by too much can lean out the mixture (but that is easily fixed by tuning).

Back onto topic, 2 turbos can be more efficient than 1 turbo in some circumstances, it really is impossible to generalise.

[PM-R33]

The temperature of the air is a very interesting factor, because most engines measure it BEFORE the intercooler and turbo, so it does assume certain variables after that fact. The AFM measures flow X temperature X pressure all at once, and changing any of those by too much can lean out the mixture (but that is easily fixed by tuning).

As far as I am aware a skyline AFM (and every AFM i've ever dealt with) only measures the amount of air passing through it in kg/h, doesn't have anything to do with temperature or pressure.

Edited April 30, 2010 by PM-R33

[Thelen]

As far as I am aware a skyline AFM (and every AFM i've ever dealt with) only measures the amount of air passing through it in kg/h, doesn't have anything to do with temperature or pressure.

The AFM is just a heated piece of metal. The 'air flow metering' is simply based on how much it is cooled. Therefore, differences in flow rate, temperature, and pressure, will ALL affect it. I'm not an engineer and don't know the specifics or how much it does effect things, but I do know this much

[mad082]

couldn't agree more volume of air and fuel make power

a big turbo @ 10psi will make more power the a small turbo @ 20psi

psi don't mean shit its the volume/mass/amount (what ever you want to call it)

of oxygen that counts

hence you make more power on a cold damp night than you would on a hot dry day because the air is denser (more partials of oxygen in the same volume of air)

that isn't entirely true. a lot of the reason why the small turbo will make less power is because it is restricting the exhaust gas so the engine is having to work harder to push the exhaust gases out of the cylinder as there is more restriction (and therefore higher pressure) in the exhaust manifold. once you reduce the restriction on the exhaust side then it can push the exhaust gases out easier and won't have as much resistance pushing against the piston. if you take 2 turbos with the same size exhaust housing but with different compressor housings then compare how much power they both make at the same pressure there won't be too much in it. the reason being that the pressure you see on a boost gauge is caused by the compressor ramming in more air than the engine can injest, thus pressurising the system. also you will have the intercooler adding restriction and that is why you will often see them saying that they only cause a 1psi drop at 15psi or something like that. that means that on the turbo side of the intercooler the pressure will be 1psi higher than on the plenum side. that is reguardless of what is pumping the air because the intercooler will only flow a certain amount of air before the pressure starts to increase inside the core. pressure is a byproduct of flow. the more air you flow the higher the pressure will be. if you keep all variables the same (so in the case of an engine, keep all the same intercooler, piping, exhaust and size of the exhaust housing on the turbo) you can't really alter the amount of air flowing through something without altering the pressure.

[PM-R33]

The AFM is just a heated piece of metal. The 'air flow metering' is simply based on how much it is cooled. Therefore, differences in flow rate, temperature, and pressure, will ALL affect it. I'm not an engineer and don't know the specifics or how much it does effect things, but I do know this much

Yeah i know how an airflow metre works I know im splitting hairs, but you said "The AFM measures flow X temperature X pressure all at once", technically it doesn't do all that as it cant distinguish between them, its all just one thing as you said, the rate of cooling from the airflow.