OTR IAT temperatures.

[Wayne001]

I was thinking of running some sort of ducting from the grill airea to the air box so it can get fresh cool air . Just would like to know if it is possible as there seems to be a lot of stuff in the

 

[LS3SS]

im not questioning any shops work im sure they are good, just have never heard any of the blower company's able to quote even down to ambient temps with there blowers let alone below it, yours is the first i have herd of with below ambient without a fridge, with your key on before engine starts dead cold does the iat match the ect or ambient ?

Sorry for the late reply; but to answer your question, iat consistently 1deg warmer than ect. Ambient not relevant in this instance, as sun warming ambient but engine retaining residual overnight cooler temps

 

[Foggsy]

In regards to IAT's and OTR's here is what I know based on personal experience. Firstly, holden put the maf over near the airbox to keep it away from engine heat and rad heat as much as they could. Thats why its over there as it gets less heat soak there.

When you run a MAF OTR either harrop or VCM the maf is located right in front of the throttle body and suffers badly from heatsoak and the OTR company just relies on still reading the IAT at the MAF. On my previous VE I had a Duspeed OTR and part of that was an IAT extension, patch harness and sensor and the IAT was effectively moved up to the front of the OTR just behind the grill. Worked Brilliant, car only read a couple of degrees above ambient when moving. Duspeed isnt currently still making em but is developing a new one I believe.

Moving forward to right now, the fact Dus isn't making them and I had to get a new car, I went with the harrop just because of the clamping around the filter quality etc etc. Anyway when fitted and reading IAT from the MAF behind the OTR it was getting up to 59 or 60+ deg at idle in traffic on a high 30's day and when driving at say 70 consistently it was still 15 deg above ambient. This means that the stock tune is pulling timing from when it reads 30 deg and over so your losing heaps of power. You can desensitise the knock/IAT sensor in the tune and for mine I did make some adjustments to that however the big thing I did to combat the whole thing was to put a new IAT in myself up the front behind the grill and now reading from there instead of at the maf, i'm generally 1 or 2 degrees above ambient when cruising. Stopped it does climb but as soon as you take off and move some air it drops right back down again. Now im not being robbed timing and power due to this IAT heatsoak issue. I have my car tuned mafless with the maf in place but just turned off.

If you run the VCM or Harrop Mafless versions of the OTR they locate the IAT in the back section of the OTR just to the side of where the maf could normally go on the maf version and this area in my opinion is not optimal and would suffer badly with IAT temps and heatsoak.

I don't have experience with ORSSOM but its fundamentally flawed anyway as an OTR as it doesn't lean the rad back and have the scoop and i know for a fact that very little air enters the usual OTR's from the top, it all comes via the scoop so.....

I could go into all of the problems a mate of mine just had with a harrop OTR trying to fit to a E3 12.5 wagon but that's a story in itself.

I don't care how good these companies claim to be, all of the OTR's out there are flawed in some way, its just whether you can work around it like I have or whether you care at all I suppose. I think for them to just take the IAT reading from the MAF is either poor engineering or they just want your money and don't care or both.

Interesting stuff.

 

[monstar]

When you run a MAF OTR either harrop or VCM the maf is located right in front of the throttle body and suffers badly from heatsoak and the OTR company just relies on still reading the IAT at the MAF. On my previous VE I had a Duspeed OTR and part of that was an IAT extension, patch harness and sensor and the IAT was effectively moved up to the front of the OTR just behind the grill. Worked Brilliant, car only read a couple of degrees above ambient when moving. Duspeed isnt currently still making em but is developing a new one I believe.

Splitting the location of IAT and Speed (velocity) measurement could only be effective if bypassing the MAF (MAFless). Otherwise counterproductive. MAFless is not always the best BTW.

I don't have experience with ORSSOM but its fundamentally flawed anyway as an OTR as it doesn't lean the rad back and have the scoop and i know for a fact that very little air enters the usual OTR's from the top, it all comes via the scoop so.....

The Orssom still flows 1500+ CFM @60 kph. Plenty for 600 hp NA. Fastest G8 in the US runs an Orssom with Maggie. Wider venturi causes unwanted / counterproductive turbulence for a stable tune and troublesome interference with radiator cooling path.

 

[07GTS]

back when i was n/a i had the vcm otr with the sensor in the rubber at the bottom just above the radiator and i had no issues with heatsoak, depending on sensor they are instantaneous in changing resistance so any hot air around it then will heat up but with a gulp of cooler air will cool it down as it flows over the sensor, also u dont have to de-sensitize your knocks just lift up the iat spark retard table u can easily go higher without issue its only that safe because its factory, i didnt start to take out iat spark till after 45c when i was n/a never had any issues, id rather have it read actual intake then just front bar ambient especially if ur SD tuned

 

[monty_vfssv]

If you run the VCM or Harrop Mafless versions of the OTR they locate the IAT in the back section of the OTR just to the side of where the maf could normally go on the maf version and this area in my opinion is not optimal and would suffer badly with IAT temps and heatsoak.

As long as the AIT sensor is in the flow of your intake, would it really matter how close to ambient your sensor is reading?

The further you go into the intake the hotter its going to be due to heat soak, but surely that would also be a more accurate temperature reading of whats about to be mixed with fuel and enter the cylinder?

 

[Immortality]

Yes and no, that's why there are two distinct sensors, AIT and MAT as used on the older Holden engines. On the newer operating systems it is often referred to as AIT1 and AIT2.

 

[monstar]

As long as the AIT sensor is in the flow of your intake, would it really matter how close to ambient your sensor is reading?

The further you go into the intake the hotter its going to be due to heat soak, but surely that would also be a more accurate temperature reading of whats about to be mixed with fuel and enter the cylinder?

Yes, accurate charge prediction is at the very core of EFI. With a blended (MAF & SD per factory) tune the intake air temp and speed vs vehicle speed and coolant temp is weighed against manifold pressure and intake valve temp to determine load / RPM hence optimum spark and fuel.
What @07GTS said was it's fine to maintain the spark a bit longer as air gets warmer but that is different to changing factors completely. Better ways to make HP than screwing with GM research into engine protection and EFI.

 

[07GTS]

MAT is the main one and if u only have IAT1 and ECT then the MAT is calculation of the cylinder charge temp table's bias between the IAT and ECT to predict MAT related to flow, so the slower the flow the higher MAT and opposite for higher flow, the closer your ecu's calculations are to correct the better it can calculate year round, its more so with blowers as i can have big difference between ambient and actual into cylinders (my charge bias table zeroed out because IAT is in manifold half inch before cylinder inlet so its actual MAT=IAT same) so i can have a zero deg day and give it a massive WOT run and say IAT=MAT gets to 70c if im still tuned to only seeing zero (if i used IAT in intake) my fueling is going to be out and ill always have to correct it so next day its 30c ambient ill have to re-tune it again for that day and so on, this is only a small part of fueling still have all injector data, transients, eoit, IVT, ITT then u add flex sensor with ever changing afr's, spark mult, transient mult, and many more.....

 

[VS 5.0]

MAT is the main one and if u only have IAT1 and ECT then the MAT is calculation of the cylinder charge temp table's bias between the IAT and ECT to predict MAT related to flow, so the slower the flow the higher MAT and opposite for higher flow, the closer your ecu's calculations are to correct the better it can calculate year round, its more so with blowers as i can have big difference between ambient and actual into cylinders (my charge bias table zeroed out because IAT is in manifold half inch before cylinder inlet so its actual MAT=IAT same) so i can have a zero deg day and give it a massive WOT run and say IAT=MAT gets to 70c if im still tuned to only seeing zero (if i used IAT in intake) my fueling is going to be out and ill always have to correct it so next day its 30c ambient ill have to re-tune it again for that day and so on, this is only a small part of fueling still have all injector data, transients, eoit, IVT, ITT then u add flex sensor with ever changing afr's, spark mult, transient mult, and many more.....