Intake Air Temp question

[Voice of Reason]

What are others seeing their IAT at compared to ambient temps? I have my DIC setup to show IAT in the center and its interesting how stop and go traffic affects it compared to an open road. On the highway I'm seeing IATs 20-25 degrees more than ambient. That's a little higher than I expected since we have a nice intake sucking air in. Are others seeing this much of an increase? Again, this increase is for open road driving, not in traffic. In traffic I see it go up a bit more than this.

 

[01sapphirebob]

There is still probaby hot air from under the hood finding its way in. I know on the GEN IV cars you could get a closeout panel from MOPAR to help with this problem.

 

[MoparMap]

Not that it's a direct comparison to a Viper by any means, but on my 5.7 swap in my old Dart I see similar numbers over ambient while cruising. Got a 6 Pack hood on it and a carb style intake so the air cleaner is mostly in direct air through the scoop. No close off plate though, so it can pull some under hood air. My cruise numbers are usually between 20-30 over ambient and can climb up pretty high around town in stop and go.

 

[PeerBlock]

I would guess that the higher temps are from the heated radiator air being blown back into the engine bay. If you don't mind going ghetto, you could probably cut it down by a few degrees by applying some type of reflective insulating material to your intake box and tube...but there's no benefit to doing so in my opinion. Pretty sure the IAT sensor is where it is on most cars, plugged into the tube that connects the air box to the intake manifold.

 

[Jack B]

The short answer, the probe of the IAT sensor is hotter than the actual intake air (not by too much) because the probe itself is not totally insulted/isolated from the engine bay heat. That added heat is primarily convected and conducted heat that enters into the sensor body from the engine side of the sensor.

 

[SilveRT8]

A trick I did with the SRT8 Jeep was to relocate the IAT sensor in a cooler location, closer to the CAI filter, so that the PCM would think cooler air is coming in and not retard the timing.
Since on the Viper the inlet tube is so short, I don't think we can relocate the 2 IAT sensors but maybe we could isolate them better from getting heat soaked by engine temp.
I'm no mechanix but just a tought.

 

[PeerBlock]

Is anyone actually noticing degraded engine performance from the IAT reading higher than ambient temps at speed? Wouldn't SRT have noticed this and compensated for it in the ECU?

 

[Jack B]

High IAT = less hp. In the past CC would throw more fuel into the engine, therefore, less hp again. The G2 over 5000 rpm would routinly run 11.5 at wot when the temp was over 80 deg.

Is anyone actually noticing degraded engine performance from the IAT reading higher than ambient temps at speed? Wouldn't SRT have noticed this and compensated for it in the ECU?

 

[PeerBlock]

High IAT = less hp. In the past CC would throw more fuel into the engine, therefore, less hp again. The G2 over 5000 rpm would routinly run 11.5 at wot when the temp was over 80 deg.

So are you saying that the V10 would benefit from an IAT relocation/insulation mod?

 

[Jack B]

If the the G5 has the same a/f versus rpm table as the previous generations it can benefit from leaning out the a/f at high rpm and wot. The G4's have seen hp gains by fooling (adding resistors) both the IAT and ECT sensors. Give Sean Roe a call and discuss it with him. This is where most of the added hp has come from on the G2 when it is tuned.

So are you saying that the V10 would benefit from an IAT relocation/insulation mod?

 

[impalassed]

A simple fix to combat the heat would be to install a spark plug boot/wire heat sock. They usually come in pairs, are readily available from local stores and are not to expensive. Plus you have all sorts of colors to choose from.

 

[SilveRT8]

A simple fix to combat the heat would be to install a spark plug boot/wire heat sock. They usually come in pairs, are readily available from local stores and are not to expensive. Plus you have all sorts of colors to choose from.

GREAT IDEA !

 

[PeerBlock]

A simple fix to combat the heat would be to install a spark plug boot/wire heat sock. They usually come in pairs, are readily available from local stores and are not to expensive. Plus you have all sorts of colors to choose from.

Pretty sure that the heat soak is caused by the radiant heat warming up the intake tube itself and not so much the sensor itself getting hot.

 

[Jack B]

Radiant heat transfer is line of sight. I would guess at the front of the engine it is also a combination of conduction and convection. Look at my IR picture (sills) and the hot spot, that is convected heat escaping the containment

[; xQUOTE=PeerBlock;3198596]Pretty sure that the heat soak is caused by the radiant heat warming up the intake tube itself and not so much the sensor itself getting hot.[/QUOTE]

 

[PeerBlock]

Radiant heat transfer is line of sight. I would guess at the front of the engine it is also a combination of conduction and convection. Look at my IR picture (sills) and the hot spot, that is convected heat escaping the containment

The easiest way to understand radiant heat is to imagine a particular object as if it were a light bulb filament. The hottest under-hood part is probably going to be the headers. If you put a light in the vicinity of your headers you will see that more than just the immediate area around them is illuminated since light reflects and bounces around just like radiant heat does.

Convection is heat transfer through a fluid medium like air or water, and yes it does contribute to heat soak, especially when the car is not moving. Conduction is heat moving from one place to another through physical contact, which would not be a big issue with the IAT sensor since plastic is not a great conductor of heat and it's not touching anything particularly hot.

I bet heat-wrapping the headers would be a solid improvement for the viper, mainly just to lower the under-hood temps and to a lower extent, to improve the flow of exhaust.

 

[Jack B]

I am a licensed thermogapher. I understand what you are trying to say. Convection/conduction is the bigger issue at that location. If I were to insulate/isolate the sensor the temp would drop far more then if I radiant wrapped the sensor.

What are your credentials?

The easiest way to understand radiant heat is to imagine a particular object as if it were a light bulb filament. The hottest under-hood part is probably going to be the headers. If you put a light in the vicinity of your headers you will see that more than just the immediate area around them is illuminated since light reflects and bounces around just like radiant heat does.

Convection is heat transfer through a fluid medium like air or water, and yes it does contribute to heat soak, especially when the car is not moving. Conduction is heat moving from one place to another through physical contact, which would not be a big issue with the IAT sensor since plastic is not a great conductor of heat and it's not touching anything particularly hot.

I bet heat-wrapping the headers would be a solid improvement for the viper, mainly just to lower the under-hood temps and to a lower extent, to improve the flow of exhaust.

 

[PeerBlock]

I am a licensed thermogapher. I understand what you are trying to say. Convection/conduction is the bigger issue at that location. If I were to insulate/isolate the sensor the temp would drop far more then if I radiant wrapped the sensor.

What are your credentials?

This would be an inexpensive and interesting experiment.

My credentials are that I'm consistently right - even when I'm not right.

 

[Jack B]

Simple experiment, I will do it some time next week.

This would be an inexpensive and interesting experiment.

My credentials are that I'm consistently right - even when I'm not right.

 

[Voice of Reason]

Bumping this back up.

I was cleaning the engine today after getting caught in the rain yesterday driving back from Road America and when I felt under the air box it feels completely sealed except for a 1.5-2" hole/tube on the underside. It must be there to drain water to prevent hydrolock because the only other thing it's doing is sucking hot air that's blowing directly at it from the radiator. I think I'm going to take the entire box off tomorrow to get some measurements, I'd like to find a rubber cap to put over it that's easily removable so I can pull it off quickly if/when I ever get caught in the rain again. Any guesses how that will lower the temps?

 

[PeerBlock]

I'd like to find a rubber cap to put over it that's easily removable so I can pull it off quickly if/when I ever get caught in the rain again. Any guesses how that will lower the temps?

It wouldn't, because the air entering the intake box is higher in pressure and cooler due to the hood scoop. Any warm air from the radiator would be displaced.