Author Topic: Air Temp Sensor Placement  (Read 14989 times)

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Offline hombre

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Air Temp Sensor Placement
« on: February 14, 2008, 04:31:21 PM »
I'm running a supercharger and custom intercooler on my Triumph Rocket 3, built for me by TTS of Silverstone. I've made several upgrades to this kit that have made significant differences. I'm now looking at their placement of the air temp sensor... which they put between the air filter and the supercharger. I'm thinking that the ECU would get a more useful intake air temp if the sensor was placed between the intercooler exit and the throttle bodies. I'd love to get some experienced input regarding air temp sensor placement on intercooled-supercharged systems.
« Last Edit: March 05, 2008, 08:21:47 PM by hombre »

Offline narider

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Re: Air Temp Sensor Placement
« Reply #1 on: February 14, 2008, 05:12:23 PM »
Do you know if it was designed as an IAT(intake air temp) or an AAT(ambient air temp) circuit?
Sounds as if the latter if that's where they designed it to go, or was the systme possibly not originally intended for an intercooler?

I know that(all else being equal in oem setups I'm used to) by putting an IAT sensor too close to the throttle body on an NA system, you can run too rich at idle if there's any reversion cooling the sensor down. I log an IAT sensor at the intake of my carbed bike to see the reversion in this way(was an easy way to help get the right length of pipes on my bike).

So depending on your intercooler's [in]capability(i don't know what kind of temps it does or does not help reduce to), could it end up just pegging the resistance limit of the sensor out and be worthless as an actual sensor if put after the supercharger?

Was the supercharger system designed to be intercooled to start with? I don't know anything about their system, but TTS seems to have a good following and grasp in the go fast stuff.

There's alot more knowedgable then I here(like most everyone), so I'm sure you'll get steered in the right direction. Personally, I'm just looking forward to seeing this run.... wish it had more of a full fairing on it though.
Todd
« Last Edit: February 14, 2008, 05:14:47 PM by narider »

Offline hombre

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Re: Air Temp Sensor Placement
« Reply #2 on: February 14, 2008, 05:33:35 PM »
TTS used the stock Triumph IAT sensor, which is designed to run in a plenum just before the TBs. This was the first R3 intercooler they have built, so I have a feeling they just used the sensor placement they use with their non-intercooled kits. They also tune their R3 SC kits without a MAP sensor, instead of upgrading to a 2 bar MAP sensor like I have (with excellent results). They did a nice job on the intercooler though... 82% efficency.

Hey Todd, I'd love to drop by sometime and have you eyeball my fairing. I built it, and I'd like to know before Maxton if it will pass tech inspection.

Offline narider

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Re: Air Temp Sensor Placement(Fairing legality?)
« Reply #3 on: February 14, 2008, 07:18:32 PM »
Would be glad for you to come by anytime and would be happy to get a closer look, call and get the secret knock first though(I'm backed up in work for well over a year so I stay in wrenchness protection quite a bit).

There's some limitations to positioning, but from what I can tell in the picture you posted I imagine your fairing will be ok(nothing I say is official unless done at the track by multiple inspectors anyway, and even then it is only the safety factors that are official as the other entrants are the real judges in the legality of your classification).

Tech inspection is for safety, but overall the requirements for fairing use pretty much come down to being securely mounted in 3 places or more, not being able to contact the tank or frame, not able to interfere with the controls and not hiding the rider more then the Partial Streamlining rules allow).
 
So come on out and let some of our twins and fours get a giggle at that three breasted wonder  :-D
Todd

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Re: Air Temp Sensor Placement
« Reply #4 on: March 05, 2008, 11:20:19 AM »
The IAT is used to compensate for the changing density of the air charge due to temperature. I would expect this sensor to need to see the temp of the charge going into the cylinder which means after the forced induction and after the intercooler. However, if the system was mapped with it before the S/C and I/C then moving it now may introduce an error into the existing maps. Of course, measuring it where you are is introducing an error into the system. The only real solution is to move it and fix the maps.

Offline hombre

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Re: Air Temp Sensor Placement
« Reply #5 on: March 05, 2008, 07:57:34 PM »
The IAT is used to compensate for the changing density of the air charge due to temperature. I would expect this sensor to need to see the temp of the charge going into the cylinder which means after the forced induction and after the intercooler. However, if the system was mapped with it before the S/C and I/C then moving it now may introduce an error into the existing maps. Of course, measuring it where you are is introducing an error into the system. The only real solution is to move it and fix the maps.

My thinking exactly! I think Todd is correct that TTS placed the sensor upstream of the supercharger due to max temp abilities of the sensor in the non-intercooled version... that compressed air gets hot! I just bought my own DynoJet 250i, so I'm actually looking forwards to moving the sensor and tweaking my mapping.

Offline ddahlgren

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Re: Air Temp Sensor Placement
« Reply #6 on: March 19, 2008, 07:33:41 AM »
The air temperature rise under boost is constant in that it will be the same amount of rise over ambient for a given amount of boost. If you put the air temp sensor in a place where it can heat soak you will have more problems than the potential to run slightly rich. I would measure the air temp into the turbo or supercharger especially if the intercoller is not all that good. These sensors can only go so high typically 257 degress and can easily fail one perminently on a heat soak situation or high boost with a poor or no intercooler. The results will be the same either way.
Dave

Offline GH

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Re: Air Temp Sensor Placement
« Reply #7 on: March 19, 2008, 10:17:05 AM »
We are in the process of installing a Megasquirt unit on the #1950 Buick just for datalogging purposses. It is blown with a 4-71 roots blower, we are going to log IAT both before and after the blower so we can compare the difference.

Offline ddahlgren

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Re: Air Temp Sensor Placement
« Reply #8 on: March 19, 2008, 10:41:23 AM »
You would be better served with a thermocouple on the before side as the temps will no doubt be over 257 easily with any amount of boost and a roots type blower they are only around 50 to 55% effecient and you are starting with 90+ degree air..
Dave

landracing

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Re: Air Temp Sensor Placement
« Reply #9 on: March 19, 2008, 10:48:10 AM »
I have placement of my air temp sensor in the plenum right after the throttle body. It is in the direct airstream coming out of the TB.

As Dave has mentioned already be carefull of plastic temp sensor where it can heat soak. I have seen first hand where they melt and look like the inside of a cheese stick... Not good, since a good setup EFI system uses this data parameter for fuel corrections.

And if placement is in the plenum and your melting it, you have bigger problems...

Jon

Offline hombre

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Re: Air Temp Sensor Placement
« Reply #10 on: March 23, 2008, 09:24:28 PM »
The air temperature rise under boost is constant in that it will be the same amount of rise over ambient for a given amount of boost. If you put the air temp sensor in a place where it can heat soak you will have more problems than the potential to run slightly rich. I would measure the air temp into the turbo or supercharger especially if the intercoller is not all that good. These sensors can only go so high typically 257 degress and can easily fail one perminently on a heat soak situation or high boost with a poor or no intercooler. The results will be the same either way.
Dave

Thanks for your input, Dave. The problem is the boost is not constant. It varies from zero at idle (with blow-off valve) to 14psi at 7000 RPM. So with the boost being fairly linear, it's about 7psi at 3500 RPM and the temp rise is way different than at 7000 RPM. Therefore, keeping the sensor in the air filter (before supercharger) doesn't allow the ECU to control AF for IAT in a precise manner.

The intercooler has good efficency... I've yet to record a temperature that would damage the IAT sensor. I'm going to try moving it to just before throttle bodies, and will report back.

Thanks to everyone for the replies!

Offline dieselgeek

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Re: Air Temp Sensor Placement
« Reply #11 on: March 24, 2008, 01:53:09 PM »
I always recommend putting the IAT sensor AFTER any compressor or intercoolers, so the EMS knows the temp of the incoming air as accurately as possible.   I'm not a rocket scientist, but I woudl think that other barometric factors would affect the "scaling" of the ambient temp.  If you have a heatsoak problem, that should be obvious and correctable...  keep us posted on your progress,

-scott

Offline ddahlgren

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Re: Air Temp Sensor Placement
« Reply #12 on: March 27, 2008, 12:01:34 PM »
If you take a look at the math for charge air temp I think you will find that it is very predictable. If the effectiveness of your intercooler is varible and not linked to ambient temps then you have a problem. This is typical of the drag race type ice water intercoolers that lose effectiveness over time because the water is changing temperature. If you really have to have it after the intercooler which I have done often as well just keep it away from anything that will hold heat ie. large mass as it will dampen the sensor response.
Dave

Offline dieselgeek

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Re: Air Temp Sensor Placement
« Reply #13 on: March 27, 2008, 01:44:20 PM »
I see your point Dave. 

But from the "how EMS's usually work" standpoint, that being most of them use just the ideal gas law for their gamma enrichments (barometric adjustments that the end user is usually not allowed to tune), I know only Motec lets you go in and adjust the algorithm that calculates fuel as a function if IAT...

I've tested a lot of other standalones out there, I know for sure that a guy with a BigStuff3, Gen7 DFI, or FAST (which share a lot of code and hardware) is going to want his IAT sensor *after* the intercooler so he at least has a fighting chance of consistent AFRs with increases/decreases in charge temp.


Feel free to correct me where I am wrong because Experience > Lab Testing any day of the week!

-scott

Offline ddahlgren

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Re: Air Temp Sensor Placement
« Reply #14 on: March 27, 2008, 04:46:05 PM »
I don't use any of those systems to be candid or at least not any more but there is a common connection. The same person was involved in the design of all 3 go figure.. I had thought with the gen 6 dfi you could adjust the air temp correction for fuel.. though maybe wrong and it has been a very long time since I have had the software up and running.. I do know the motec haltech and efi tech all allow for these adjustments. I generally follow the ideal laws when the temps are withing the range of sanity I deviate when the IAT starts getting to high that I am in danger of hurting the engine I start putting fuel back in to cool it back down even if it runs worse. The motec has the luxury of having a driver warning alarm lite go off when sensors are saying things are out of bounds.. The proverbial check engine lite. Their dash has the greater luxury of conditional alarms such as if oil pressure below 40 and rpm above 8000 send this message in the text screen for the warning.. I programed one for 'THIS RIDE OVER' for the above mentioned condition..LOL
Dave