Nissan HotWire Maf with IAT sensor purpose

[kpjo4]

Since a hotwire maf can get the density of incoming air charge through the hot wire changing resistance due to air cool effect what is the purpose of the IAT? I understand the IAT is not needed to run a car, for example a sohc ka24e maf on a sr20det; you would just use the maf and not the extra IAT sensor on the factory airbox of a ka24e. So what purpose would it serve? Just trying to kill my curiosity.

[fliprayzin240sx]

I know on my first 240sx, the IAT was used by the ECU. Depending on the temp it's sensing, it would advance/pull as much as 5* of timing IIRC. We used to trick the ECU by replacing the sensor with a resister to keep it from pulling timing. The good old days of not having decent parts for a KA.

[foreverdeath]

Maf will give you density but the IAT will provide a temp allowing for a more accurate fueling. As air temp also helps to let you know how aggressive your time can be, so you don't detonate. Most newer hondas have both a MAP+IAT sensor and a MAF sensor of accuracy.

[Kingtal0n]

its not used for fueling, the maf measures the mass of air there is no reason that an IAT could do any better.

its for timing. A large mass of really hot air vs an identical mass (but much less volume) of really cold air- the cold air should get more timing advance, despite it having the exact same weight as the hot air.

Keep in mind you will always make the most power with the largest mass of hot as possible air. Fuel octane casts a limitation on how hot you can get before problems, generally, which is why we still shoot for colder air. If octane wasn't an issue then the timing coming in or out with colder vs hotter would not make a difference. The manufacturers are trying to prevent problems regarding octane vs temperature. It has nothing to do with air fuel ratio being changed.

bored

[e1_griego]

From what I remember from the HybridKA forums (anyone remember DeviousKA??), the IAT has the authority to pull up to 8* of timing depends on temp.

The early 9:1 KA (pre 11/88 build date) didn't have the IAT, and after 11/88 the KA became 8.6:1 and added an IAT. This is an easy method of identifying the higher comp SOHC.