Reasonable to force users to run both MAT AND IAT always?

[AbeFM]

I'm a little confused here, so I'll ask some questions. Basically, everything till the last couple paragraphs has a big question mark after it.

MAT - Manifold Air Temperature
IAT - Intake Air Temperature

The MAT is the temp measured inside the manifold. This should be susceptible to heak soak, as the hot manifold will heat the sensor.
The IAT is the temp in the IC piping, but after the intercooler. This is the temp of the air as it inters the manifold.

The MAT, depending on where it's mounted, is really just there to get a feeling for the drift in the temperature away from what the IAT was reading. This will including heating due to pumping effects through the throttle plates, and heating due to heat absorbtion from the manifold. If your MAT is mounted right at the entrance to the manifold, and you have long or variable/complex runners, you would expect it to read low anyway (though this overlaps with the errors inherent in measuring MAP)

So, since MAT is being used with MAP to get the actual count of air molecules in the manifold, that is what you should be using most of the time, and the IAT is just there to show you how wrong you were due to heat soak.

Certainly, to my mind, multiplexing a few inputs is the way to go. This is not super-time-critical information, as it's a second out of date at all times anyway. So, this would be a great case for something like an external chip/circuit that either switched between them or whatever.

My best suggestion would be to use a thermocouple in the manifold. They are much much much faster. People avoid them since the readout circuitry is more complex. But heat soak isn't an issue, it would equilibrate in a very short time, radiative thermal coupling to the manifold notwithstanding.

Really, how long does it take to empty the manifold? Just fudge the numbers for the first few engine cycles (or, minutes?) to be a bit leaner, based on coolant temps, and be done with it. If the coolant temps are low, there's no heat soak, you can trust the sensor. If not, there's a fudge factor you can let for for a while.

The option for more sensors is nice, but I don't think it should be forced, I'm not sure I see the gains.

[Fred]

The MAT, depending on where it's mounted, is really just there to get a feeling for the drift in the temperature away from what the IAT was reading.

Agree.

So, since MAT is being used with MAP to get the actual count of air molecules in the manifold, that is what you should be using most of the time, and the IAT is just there to show you how wrong you were due to heat soak.

Disagree.

My best suggestion would be to use a thermocouple in the manifold.

They also don't come stock on your 1995 rb25det etc etc. We want the core feature set to be applicable to anyone/everyone.

Really, how long does it take to empty the manifold? Just fudge the numbers for the first few engine cycles (or, minutes?) to be a bit leaner, based on coolant temps, and be done with it. If the coolant temps are low, there's no heat soak, you can trust the sensor. If not, there's a fudge factor you can let for for a while.

Excellent idea. Coolant and manifold are going to be fairly closely related for certain. Additionally, if such a correction was used, it would be in a user definable table of sorts. A super strong recommendation to put your IAT in an intelligent place could be plastered in bold flashing neon on the website front page and people that adhere to it should have minimal issues.

The option for more sensors is nice, but I don't think it should be forced, I'm not sure I see the gains.

Agreed, and esp in light of you stating the obvious (which I was blind to) about coolant temp for heat soak of air.

Thanks for the post, good work.

Admin.

[AbeFM]

I do think that's the best way out, the rest is hashing out theoretical details (which, well, I do for fun).

So, getting to that, why do you not like using the MAT? Just because it is so prone to error? (That's ENTIRELY reasonable)

My question is, if you had a 100%, idealized MAT, with no radiative coupling, no heat soak, it just somehow knew the exact temperature in real time of the air in a particular place.... Why would you mount it outside of the manifold?

I would think you'd want the MAP and MAT to be in the same place at the same time, since really you're just counting molecules/sec entering the engine.


If it were me, I'd have four flow meters, one in each runner, and do my fuel and timing based on that, with direct injection. To quote our beloved Jean-Luc: Make it so.

[Fred]

So, getting to that, why do you not like using the MAT? Just because it is SO prone to error? (That's ENTIRELY reasonable)

Fixed it for ya. Correct, they are rarely an accurate representation of incoming air temperature. The transfer of heat from manifold and tubes etc to the air is negligible unless the air is stagnant. Therefore the external IAT on the outlet of the cooler near the front of the car is the best representation of air temp. My thoughts when posting this thread were two fold. Forcing people to use two would give you a good way to judge things at startup/idle, AND, it would force them to realise what the difference is.

It is unfortunate that this has been ignored and confused in MS docs over the years to the point where some hardware has MAT on it and some IAT, but they all mean the same thing. They are not the same thing.

My question is, if you had a 100%, idealized MAT, with no radiative coupling, no heat soak, it just somehow knew the exact temperature in real time of the air in a particular place.... Why would you mount it outside of the manifold?

You wouldn't. That would be ideal. However we are living in the real world :-)

I would think you'd want the MAP and MAT to be in the same place at the same time, since really you're just counting molecules/sec entering the engine.

Ideally yes, really, no.

To quote our beloved Jean-Luc: Make it so.

LOL, I haven't seen an episode of that for about 13 years!

Admin.

[AbeFM]

As in Love, Fred again teaches us the value of paying attention to the harsh realities of the real world verses the idyllic hopes one might have based on how the world should be.

Thanks! I think I've got a better understanding of it myself now, and the thread should be (brief) required reading.

Edit> Vote Cast!

Also, the coolant-based-leaning leads into something I was thinking about today....
http://www.diyefi.org/forum/viewtopic.php?f=8&t=228