Is the temperature read before or after the throttle?

 

All I know is it's before the tailpipe
I'll check in the FSM for an intake sensor.

As for pressure, maybe the pressure drops as a function of increased throttle due to more vacuum at higher RPM... But again that change is only evident between light throttle and zero throttle. At moderate throttle, no additional temp drop occurs.
But this little bit of change is not particularly substantial. Just a curious thing.

 

Could be voltage fluctuations too.

A quick report, data logged my whole trip to work and then couldn't figure out how to save it. So, stopped for coffe on the way in and I switched to display mode looking at IAT's. I started the car and temps were at 159 degrees. Once I pulled out and began moving in stop and go, 30mph speed limits, the temps dropped really quickly into the low 120 range. Had I been able to accelerate more quickly to a higher rate of speed, I'm sure they would have dropped even further.

 

Your supposition would be true if the temp is read before the throttle plates. At WOT, intake pressure is at its highest after the throttle. At idle, it's lowest. Note I wrote pressure, not vacuum.

The unchanging temperature at part throttle is curious.

 

We're naturally aspirated, we never see positive pressure and there's no ram air effect. Maybe at WOT at redline and slam the tb's closed. I'll data read map pressure and report back. Should read lowest vacuum point

 

Hmm. Interesting.
Either way I think the takeaway is that since the intake temperature consistently increases 2-4 degrees, whenever the throttle position drops to zero, regardless of the vehicle speed, that there is at least a minimum of a 4 degree margin of error or variation when comparing intake temperature differences between intakes.

I would not be surprised to find even more than 4 degs margin of error or variance due to other factors.

 

Ha!
Yes I considered the Laminar flow effect and the insulating effect but when my calculations showed how insanely brief any particle of air spent traveling through the midpipe I realized I didn't need to investigate that any further.

The calculation was kind of fun actually. I thought I was way off and set it aside to redo it again later even though I knew it was going to be really small. Glad to see your estimate of a few milliseconds is in line with what I came up with.

So we can eliminate the midpipe as a substantial contributor to the intake temperature.

If you still can't get a decent data log from your app, give Dash Command a try.

 

That was a total guesstimate but glad I was close!

I really wonder how accurate the IAT sensor is. Could be off. It's obviously not a "dummy" sensor like our O2 sensors are and it has to have somewhat of a decent resolution as the timing tables and fuel tables would require it.

You know, if you're inside a house and the house is 75 degrees, you turn on a fan and you "feel" cooler due to the air volume carrying off your body heat. Could be the same principal. The rushing air keeps the sensor's temp at the air's temp and not what the body of the sensor is at due to heat soak through the hard parts. Slam the throttle shut and there goes your airflow and cooling effect.

 

Hee hee... Excuse me while I go get my propeller hat

This is addictive discussion. Okay, again, the way I see it, since it (2-4deg temp increase at zero throttle) is consistent, predictable and rather small, it's academic but... that's a compelling supposition!



Thinking about the thermostat in my hallway, if I put a fan over it, the temperature does not change. (provided there is air temperature in that room is fairly homogeneous ).

While a fan makes the body feel cooler it is mostly due to the evaporation of moisture from the skin. Assuming nothing in the intake path is sweating, nothing should change much unless the temperature of the air being drawn in changes, or the closed throttle allows the air to draw heat from the walls of the chamber...and based on our discussion above it's still moving too fast through the chamber for that.

Oh crap, but then radiators exchange heat pretty efficiently without sweat...exponentially more surface area though.

I'm thinking an intake airflow temperature monitor would have very limited accuracy if it were affected by blowing air. I would hope they isolated that particular variable.

 

BUT your thermostat doesn't have a large heat source or a current of electricity flowing through it. And yes the radiator with its large surface area and use of heat conducting aluminum makes the difference. But if you spray water on it, like they sometimes do with inter coolers (or alcohol/nitrous), their "efficiency" is greatly increased. Brake ducts too... Makes a big difference. So maybe the temp differential and size of the mechanism measuring the air temp matters.

 

Also, consider our mass airflow sensors and how they use temperature to determine mass air flow.

 

Monitored the temps on my way home tonight. Ambient, once on the highway, was 87 degrees (@10pm!) and my IAT's were 93.2 degrees. So the whole heat soak thing is a non-issue. Yeah, it heat soaks at idle but I could care less what the IAT's are when I'm standing still. They drop pretty rapidly once moving at anything over 25mph. We'll see what the Nismo produces temp wise.

 

Ha, beat me to it again.
I was just looking in the FSM for where the temperature sensor is, then googled it for the VQ and confirmed the MAF has the tempature sensor built-in.

So yes to answer an earlier question the intake temperature is taken in the midpipe at the MAF sensor.

 

Also it's good to see the temperature differential is in the very same +6-10 deg over ambient range as I captured with the OEM intakes.

So the idea of heat soak is really a non issue except for standing still and quite frankly, my performance concerns focus on when the car is moving which is 99 percent of the time I'm operating it.

Heat might be an issue for drag racing... might.

Looking forward to installing my R2C and seeing the data.

 

I had a feeling it was integrated (makes sense) but wasn't sure if it was in the upper intake manifold either...