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Old 07-15-2008, 11:31 AM   #1
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Default WI and false IAT's

With the water spraying on the IAT, I don't understand how a true IAT measurement can be taken. I don't want to relocate the IAT into the manifold plenum until I'm forced to do a rebuild and it's already off.

Normally while in boost my IAT's are 2-5C over ambient. When the WI kicks in the IAT's drop around 10C, which would be way below ambient.

Does anyone care about this?
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Old 07-15-2008, 11:56 AM   #2
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It is definitely possible for the IAT's to be below ambient. When the mixture evaporates, it is endothermic, so you are actually removing heat from the charge. If you rub isopropyl alcohol on your hands, they feel cold. Same concept.
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Old 07-15-2008, 12:53 PM   #3
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As long as the IAT sensor isn't being soaked I don't see an issue either. BTW, the intake on Methanol fueled dragsters will frost up.

I believe you are witnessing one of the true benefits of the Meth mix.
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Old 07-15-2008, 01:28 PM   #4
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If you spray water directly in front of the sensor you are bound to get artificially low readings. Moving the IAT into the IM might also give you artificially high readings due to heat soak from the IM itself.
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Old 07-15-2008, 01:30 PM   #5
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How about putting the sensor upstream of the WI nozzle? Seems to be the easiest solution IMO.
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Old 07-15-2008, 01:52 PM   #6
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IAT upstream of the WI won't catch any of the cooler charge that the WI gives. So that is definitely not a true reading.

I've had manifolds (Racing Beat Dellorto sidedraft setup) sweating and cold to the touch from the fuel vaporization. I understand that. I also understand that WI cools things and steam cleans carbon. That's why I installed it.

I've got the WI to fire in different methods. I do have a manual override so I can fire it whenever I want, provided that the fuel pump is on. (that's my safety to not hydrolock the motor - hopefully). I can pulse the WI for just 1/4 second and the IAT's plummet for 20-30 seconds. No way that's a real reading.

The thing I see happening is that the IAT gets wet and will remain cool until it dries off.

I will have a data point someday when I relocate the IAT halfway down the plenum. Until then, I was just wondering if anyone takes this into account when tuning.
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Old 07-15-2008, 03:37 PM   #7
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Quote:
Originally Posted by dvcn View Post
IAT upstream of the WI won't catch any of the cooler charge that the WI gives. So that is definitely not a true reading.

I've had manifolds (Racing Beat Dellorto sidedraft setup) sweating and cold to the touch from the fuel vaporization. I understand that. I also understand that WI cools things and steam cleans carbon. That's why I installed it.

I've got the WI to fire in different methods. I do have a manual override so I can fire it whenever I want, provided that the fuel pump is on. (that's my safety to not hydrolock the motor - hopefully). I can pulse the WI for just 1/4 second and the IAT's plummet for 20-30 seconds. No way that's a real reading.

The thing I see happening is that the IAT gets wet and will remain cool until it dries off.

I will have a data point someday when I relocate the IAT halfway down the plenum. Until then, I was just wondering if anyone takes this into account when tuning.
Hmm, like you said, there is going to be heatsoak from your manifold. Also, i have heard of problems with the vibrations harming the sensors. I would really like to hear some real input on this though. I am really considering doing this on my built motor before i put the intake manifold on.
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Old 07-15-2008, 03:39 PM   #8
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Quote:
Originally Posted by dvcn View Post
IAT upstream of the WI won't catch any of the cooler charge that the WI gives. So that is definitely not a true reading.
Right, but wouldn't you rather have an artificially high IAT reading than artificially low? No harm can come from artificially high, but low would cause the ECU to add in timing, could that not be a bad thing?
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Old 07-15-2008, 04:18 PM   #9
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Originally Posted by kotomile View Post
Right, but wouldn't you rather have an artificially high IAT reading than artificially low? No harm can come from artificially high, but low would cause the ECU to add in timing, could that not be a bad thing?
Maybe you could put a little guard in front of the sensor to keep water from getting on it so much?
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Old 07-15-2008, 08:20 PM   #10
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Quote:
Originally Posted by wes65 View Post
Hmm, like you said, there is going to be heatsoak from your manifold. Also, i have heard of problems with the vibrations harming the sensors. I would really like to hear some real input on this though. I am really considering doing this on my built motor before i put the intake manifold on.
I hadn't considered mechanical damage to the IAT from vibration. I wonder how bad it is on our motors. I'm pretty sure I've seen oem's putting IAT's in the manifold.

Yes, I'm being ---- about this whole thing. I'm not even tuned well enough for this to matter - right now.
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Old 07-15-2008, 09:00 PM   #11
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What about moving the nozzle back so the water has some time to evaporate before the charge hits the IAT sensor?
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Old 07-15-2008, 10:19 PM   #12
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Why not just place the nozzle after the AIT sensor? That's what I did.
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Old 07-15-2008, 10:52 PM   #13
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Originally Posted by Savington View Post
What about moving the nozzle back so the water has some time to evaporate before the charge hits the IAT sensor?
This is kind of what i was thinking. With decent atomization and decently high AIT's it would evaporate in maybe 12" Winter would take longer maybe.
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Old 07-16-2008, 04:47 AM   #14
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Quote:
Originally Posted by dvcn View Post
With the water spraying on the IAT, I don't understand how a true IAT measurement can be taken. I don't want to relocate the IAT into the manifold plenum until I'm forced to do a rebuild and it's already off.

Normally while in boost my IAT's are 2-5C over ambient. When the WI kicks in the IAT's drop around 10C, which would be way below ambient.

Does anyone care about this?
Umm buddy these manifold temp change can even be felt on the outside of the manifold if you like WI is just that damn effecient if done correctly. From your description you have yours working just fine good job.
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Old 07-16-2008, 09:34 AM   #15
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Umm buddy these manifold temp change can even be felt on the outside of the manifold if you like WI is just that damn effecient if done correctly. From your description you have yours working just fine good job.
There is no question that it works.

I don't like dummy gauges, inaccurate or incorrect measurements, especially when it's an input to calculating fuel and ignition. I'll let it go, I know I'm being nuts. Old habits are hard to get rid of sometimes.

I can put the nozzle about 18" further upstream right at the IC outlet. I doubt this will do anything. W/o WI, the IAT reads 2-5C above ambient under boost. I have a feeling that most of the vaporization happens as things get hotter - in the manifold or in the runners, at least with my oversized IC.

Multiple thermocouples would tell the story, but it's not that important.

I had just asked if anyone cares about false IAT readings and I think the unanimous consensus is NO!

Thanks for the responses! I'll let it go now....
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Old 07-16-2008, 11:19 AM   #16
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Weld a bung to your intake tube that brings the IAT sensor out so it is no longer in the direct stream. You should still get accurate air temp readings, and get less direct spray from the WI nozzle.
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