Experimenting with Intake Air Temp. Request for comments.

juld0zer

If i was doing it, i'd be looking into sourcing a sensor designed for the purpose. Most of the automotive sensor manufacturers would have a few in their arsenal that are tolerant of manifold heat, vacuum levels and also be airtight. The S2000 has one of those sensors, not sure who makes it though. Another benefit of using a sensor designed for the purpose is they're pretty cheap from a wreckers yard and you'll get the pigtail with it to make a secure connection too.

The next part would be getting the scaling/resistance vs temperature chart and syncing that with your datalogging gear/spreadsheet. If you were to run this sensor as the engine's IAT sensor then you'd need to pick one with scaling that's exactly the same as the OEM one, or very close to it. From comparing a few (Denso) sensors and their scaling curves with the OEM one, i'm concluding that an air temp sensor which has a Denso curve would be most suitable. They're used on a lot of Japanese cars and the curve is close enough to the OEM one - unless you want to buy the entire MAF sensor to avoid any slight variances.

The problem with these manifold tolerant sensors is that the probe is usually coated in plastic to ensure long term survival, which dulls its response time. You could melt the plastic off and use it temporarily but i wouldn't expect it to last in the long run.

The 370Z FSM states 1.8-2.2kOhm resistance @ 25*C/77*F air. 0.283-0.359kOhm resistance @ 80*C/176*F air.

Mazda3 FSM states 2.21-2.69kOhm resistance @ 20*C. No mention of what resistance at higher temps though. This MAF sensor is used in heaps of late model Mazdas (2/3/5/6/CX7/MS3) and the thermister is easy to cut off. This is the thermister i am using and that is probably why my IAT as seen by the ECU reads a little warmer than the onboard ambient temp sensor.

Air temp sensor as used on late model Mazda Proteges (looks like an stake-end) has a plastic covered probe. Mazda3 turbo diesel (non-USDM model) FSM states 2.21-2.69kOhm resistance @ 20*C water and 0.29-0.35kOhm resistance @ 80*C water. Figures are based on water temps because this probe is fully sealed. I've owned the Mazda3 T/D so that's why i had a spare sensor, which i hacked up to mount the above IAT thermister (remember my pics?)

Air temp sensor as used on RX7 (screw in type, with plastic coated probing end) has identical scaling to the Protege sensor. On the RX7, this sensor is screwed into the metal intake manifold.

Relocation i think for the Z is crucial as the area around the Bank 1 (MAF/stock IAT) side of the radiator is a lot hotter than the area around the Bank 2 side. Wrapping my MAF sensor with the neoprene stuff didnt make much difference. Sucks that the fans dont come on until almost 100*C coolant temp so there isnt air to circulate around the engine bay when you're at the lights - things keep getting hotter as the engine gets warmer. I contemplated Uprev purely for the fan control but it's not cheap to remedy something Nissan should've done - damn modern emissions restrictions!

I think i mentioned somewhere in another thread that there's some healthy discussion on the Corvette/GM forums (and the Holden forums in Australia) about HSRKs, choice of sensor location (behind fascias, at the mouth of the intake, the neck of a pod filter, just before the throttle body, etc etc). My stance on this part of the debate is that unless the engine is pinging, i'm not going to worry. Like yourself, i also think that the ECM does some massaging of the sensor output. The IAT reading you get on OBD2 readers is what the sensor sees, not the final (digested/processed) temperature used to determine ignition timing and fuel injection amount.

As for the throttle body coolant bypass... i'm on the fence on this one. It's quite an involved mod to do esp with air bleeding etc so i'm not that keen on this one. As for potential gains, it would be similar to wrapping the MAF tubes to prevent radiant engine heat affecting the MAF sensor. Removing the hot coolant from the TB is like blocking the radiant heat from the engine.

Although, if the ECM does indeed apply some calculation to the IAT detected temperature, the ECU won't even notice that the air passing thru the TB is now slightly cooler. Another argument is that the air doesnt spend long enough in the TB to get warmed - you can wave your hand thru a flame and not get burnt but if you hold your hand there then it'll be a different story.

Either way, I really doubt Nissan would use a different TB (a non-coolant warmed one) in regions where sub zero temperatures never occur (eg. UAE, Malaysia, etc) but it would be interesting to get some input from members from these regions. The Aussie 370Z has coolant passing thru the TB.

SouthArk370Z

Wow! Lots of great info but I don't think you understand the scope of this project. But that doesn't mean I don't appreciate the input - I find it interesting and it may come in handy later on.
The main purpose is to see if a cheap, DIY insulation job will have much of an effect on intake air temperature at the manifold. Any increase in performance will be nice, but the goal is to see if it's possible to keep AIT within "reasonable" levels with little investment of time and money. My target is ~95°F (which I believe is where the ECM starts reducing engine output) or a delta T from ambient of 3-5°F at speed and 10-15°F at a stop light.
I do not plan on using any of my temperature sensors to replace/augment the AIT sensor and the sensors will (probably) be removed at the end of the test. They are strictly for measurement/logging. I will try to insert a sensor next to the AIT sensor for comparison (might give a clue as to whether or not the measurement gets tweaked by the ECM). I plan on putting a sensor in the manifold, the entrance to the duct work, and the TB inlet - but positions may change depending on what I run into.

BTW, the sensors I ordered are waterproof DS18B20 (1-Wire digital temperature sensor/transmitter, –67°F to +257°F) with 2 meter leads. I'm not sure how well they will handle partial vacuum, but the pressure shouldn't be very low upstream of the TBs, so the manifold sensor should be the only one in any danger.
The meter/logger's fastest sample rate is 2secs/scan, but that should be more than fast enough for my purposes.

Yeah. Probably not a big heat source, but one of those "As long as I've come this far, might as well try it" things for me.
I think I can run a bypass line (I can't tell if it will hurt anything to block the flow completely, else I'd just insert a small ball valve in the line) and plug the existing piping.

I wish I could find out exactly what the ECM does with the AIT sensor data - how it may be massaged, is heat gain after the AIT calculated, assumed, or ignored. If the engineers factored in heat gain after the AIT sensor, my insulation may turn out to have an adverse effect on efficiency.

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SouthArk370Z

The 4-channel temperature logger came in today.

I was able to install drivers and talk to the logger on my desk and laptop computers. Unfortunately, it does not timestamp the data, so synching with OBD data may be tricky. Waiting on the probes now.

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Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

SouthArk370Z

I finally got the temperature probes installed and working. One probe next to the car's ambient sensor, one at the intake inlet, and the other two are in the engine compartment near the MAF and TB (I'll have to drill some holes to get them into the duct). I thought the engine was cold, but the engine compartment probes says it's still a few degrees above ambient. Waiting for it to cool down so I can compare the four probes.

I have most of the right side duct insulated - just need to do something about the corrugated part - and have started on the left side duct.

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Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

SouthArk370Z

Due to health problems, this project has been moved to the bottom of my priority list. If anyone has a use for the temperature logger (and probes), I'll let it go for a self-addressed, pre-paid box. PM me.

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Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Sh0velMan

I'll take it

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juld0zer

mate, i hope your health has been ok. look after yourself

it's been a while since i've been on this thread but i have some updates to share:

AEM CAI installed for 3 days but removed it due to very disappointing performance. The car ran like a dog. Shifting was sloppy and jerky. Suffered extremely badly in the Sydney summer heat. I could barely overtake econoboxes and trucks. Timing was being pulled that much. I think it was a bad design. the air filters are located in dead zones. zilch fresh air. RHS is right next to the blazing hot power steering lines. Hated driving the car. I experienced intake temps over 56*c with an ambient around 38*c. I might be expecting too much but is it too much to expect at least an on par with stock level of performance and driveability?

Couldn't wait to put the stock system back on and the difference was night and day. I could love driving my car again!

The best i can get with the stock intake is 5 degrees celsius above the ambient temp displayed on the dash. This is at 50-60kmh and above, ambient at 28*c or less. once ambient goes up, the delta changes. No changes to my airboxes. The are as per my previous post in may. I cant remember if i mentioned i have flex duct jammed inside each snorkel/duct which reaches to the same position as the Stillen G3 CAI filters. This helped delay the ingestion of hot air when stationary.

Next step for me was to find some foil backed bubble wrap type insulation material and wrap the accordion pipe and the airboxes depending on space. Good reports on other forums.