Accuracy of IAT for speed density tune
11-25-2015 | 01:05 PM
#1
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Accuracy of IAT for speed density tune If using a speed density tune, how important is it that the IAT be dead-nuts accurate as to the temperature of the intake?
I'm using ITBs that stick through the hood and I'd rather not drill one of the trumpets, so I was thinking about just sticking it around a vent away from the engine (since air entering the vent should be roughly same temperature as air entering the trumpets).
Also, are these sensors very sensitive to dirt - i wasn't certain if I could just weld a bung somewhere and leave it exposed to open air, of if i should get a small can (e.g., catch can), attach a filter to the top and the sensor at the bottom so the filter keeps it clean.....
I'm using ITBs that stick through the hood and I'd rather not drill one of the trumpets, so I was thinking about just sticking it around a vent away from the engine (since air entering the vent should be roughly same temperature as air entering the trumpets).
Also, are these sensors very sensitive to dirt - i wasn't certain if I could just weld a bung somewhere and leave it exposed to open air, of if i should get a small can (e.g., catch can), attach a filter to the top and the sensor at the bottom so the filter keeps it clean.....
11-27-2015 | 08:37 AM
#2
The sensors are accurate to about +/- 2 degrees at worse case. I have done several stack setups and have just used a bracket to the back of the intake area. They are not affected by dirt at all. It's open air but the actual sensing element is covered in epoxy.
11-28-2015 | 01:41 PM
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11-30-2015 | 05:01 AM
#4
It really depends where you live. In Florida, the temp here never really hits freezing and below, so there is no opportunity (or need) to hit deeply cold-day values. If you drove the car from Florida to somewhere freezing, it might need an adjustment then suddenly.
Next, think of this. As temperature increases, air density drops and so less fuel is required. OEM computers will generally follow this trend: as air temp goes up, global fuel % goes down. The opposite is of course true for cold temps, more fuel is added when air temp drops. There may be some point at which fuel returns on an OEM map (excessive high temperatures) where fuel may be used to cool the engine off. It depends on the manufacturer.
Knowing this, you should not have trouble with the normal operating temperature tuning ranges (110-130*F air temps) because through this entire range our performance engine tuning has us adding fuel instead of subtracting it as temperatures increases, for the temperature reduction (it makes our engine safer to run on 93 octane at higher temperatures when it runs slightly richer). I never pull fuel for temp increases at the IAT.
From 70*F to 105*F you are in the warmup-enrichment region, 105-115% generally for coolant but not so much for IAT, perhaps half of that or less. So your IAT enrichment scale would look like this:
70*F - 105*F - 110*F - 130*F
105% - 102% - 100% - 104%
You want it pretty flat at 100% through the region your IAT hovers to prevent issues with tuning the base map. The difference in % fueling is so tiny you really don't even need any correction at all, as coolant temp enrichment can be used for warm-up and even depended upon solely (unless the air temp is very, very cold), and operating temperature of air usually settles at some nearly constant value (it may drop a few degrees during WOT but it generally stays put overall once an engine is warmed up) So there isn't really a pressing, dire need for air temp correction, except like I pointed out for very cold temperatures where the engine may run lean because of such cold air or if you have some other means of rapidly adjusting air temp, like nitrous or methanol injection, or a water/air intercooler. In other words, as long as you are using ONLY 93 octane on a street car, you do not even need any IAT correction at all unless you live where the air temps drop very, very low sometimes (as you can see above at most it influences 3-4% on normal occasions)
Next, think of this. As temperature increases, air density drops and so less fuel is required. OEM computers will generally follow this trend: as air temp goes up, global fuel % goes down. The opposite is of course true for cold temps, more fuel is added when air temp drops. There may be some point at which fuel returns on an OEM map (excessive high temperatures) where fuel may be used to cool the engine off. It depends on the manufacturer.
Knowing this, you should not have trouble with the normal operating temperature tuning ranges (110-130*F air temps) because through this entire range our performance engine tuning has us adding fuel instead of subtracting it as temperatures increases, for the temperature reduction (it makes our engine safer to run on 93 octane at higher temperatures when it runs slightly richer). I never pull fuel for temp increases at the IAT.
From 70*F to 105*F you are in the warmup-enrichment region, 105-115% generally for coolant but not so much for IAT, perhaps half of that or less. So your IAT enrichment scale would look like this:
70*F - 105*F - 110*F - 130*F
105% - 102% - 100% - 104%
You want it pretty flat at 100% through the region your IAT hovers to prevent issues with tuning the base map. The difference in % fueling is so tiny you really don't even need any correction at all, as coolant temp enrichment can be used for warm-up and even depended upon solely (unless the air temp is very, very cold), and operating temperature of air usually settles at some nearly constant value (it may drop a few degrees during WOT but it generally stays put overall once an engine is warmed up) So there isn't really a pressing, dire need for air temp correction, except like I pointed out for very cold temperatures where the engine may run lean because of such cold air or if you have some other means of rapidly adjusting air temp, like nitrous or methanol injection, or a water/air intercooler. In other words, as long as you are using ONLY 93 octane on a street car, you do not even need any IAT correction at all unless you live where the air temps drop very, very low sometimes (as you can see above at most it influences 3-4% on normal occasions)