Manifold air temp

[dyeager535]

My other thread reminded me about my last datalog.

I was a bit surprised at the manifold air temp (MAT) difference on the truck at idle vs. moving, even with CAI. Early truck TBI doesn't have this as I recall, but all the cars did, TBI or TPI. I believe later on truck TBI did as well.

Anyways, MAT on restart after a short shutdown and some idling was 152*. After cruising down the freeway (60MPH) for 10 minutes, the MAT was 94*. Can't recall what ambient temp was, but I'd guess in the 70's and sunny. I was just as surprised that it took so long to cool off. I had expected it to decrease much quicker, but it leads me to believe the sensor is getting some of the temp reading from heat coming from the manifold metal, not just the air. I know I've seen 3rdgen posts on the different MAT sensors.

Only rough calculation I've seen for temperature correction is 1hp gain for every 10* decrease in MAT.

A lot more testing could be done here, not sure I'm up for it though...CAI disconnected at idle, CAI disconnected at cruise, etc., different sensor design, and all with same/similar ambient temps. Really tough to tell what led to the decrease in temp. Air over motor cooling the metal, cooler air through the manifold, more air through the manifold based on RPM, etc.?

 

[MIKESMONZA]

Newbie Questions;
As you mentioned the >Manifold Air Temp (MAT),
I under stood the Heat you were Measuring,,
And You lost me on CAI ?? School Me,,

MAT;CAI,,,
Are they Present on a 87 GMC 5.7 TBI Jimmy?
or other GM FI Unit's?
or The After Market Gauge's package For a lap top Computer?
Mike

 

[dyeager535]

CAI is Cold Air Induction. CAI is probably a bit "slang", but on the GM trucks from about 1981 most, if not all, were CAI from the factory. Earlier the air cleaner drew all air from under the hood, and oftentimes you will see people remove the factory CAI, and/or add an open element K&N filter, which also draws underhood air.

Theoretically underhood air is hotter thus lowering performance, in reality I have not tested my setup without the snorkel hooked up. Kind of difficult as my TPI is MAF (which is part of the intake tract) and I have to leave it in place.

There is also IAT, which is Inlet Air Temp, measured outside of the manifold. CAI

 

[MIKESMONZA]

Thanks for the CAI intro,I should of Known
In the other Post
I was Describing the TBI Cold Air /Hot Air Door Control Actuator's
>>>THERMAC Unit mounted on Air Filter Snorkle ,
A Loss of Performance.
and thanks for the heads up on the TPI,
It Now Makes Sence,

Mike