Tony D Posted January 24, 2007 Share Posted January 24, 2007 Hell I haven't had time to do tuning, much less inquisitive testing like I want to do! >:^( There was a time, in the early 90's.... I had this job with LOTS of free time, PLENTY of pay, and that gave me unlimited access to all sorts of analytical instrumentation, complete with a private road to drive on all day Sunday---nice uphill run for load testing. That ended November 1st, 1993. For me, as well as 1499 of my compatriots at the same company all over the USA... Since then, travel jobs... Heavy Travel Jobs.... Though I still have some "neat tools" from the old job laying about. Mostly stuff I "upgraded" while there, and took the "old, outdated, obsolete for our purposes" stuff home! That hand held Omega Thermocouple Reader and assortment of probes is one of them. Actually, my wife probably has the most accurate Hard Candy Thermometer on the face of the planet (which is it's most recent 'found use around the house'). LOL!!! Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 24, 2007 Share Posted January 24, 2007 Ron, I guess my point is that if the sensor has good thermal isolation from the intake manifold, it will be an accurate reading. You are assuming that heat is conducting from the intake manifold material to the element portion of the sensor. Also, air upstream of the TB has not picked up heat from traveling through the intake manifold. There must be some sort of datasheet for the GM IAT sensor regarding thermal conduction from the sensor element to the sensor's brass case. I agree, in the case of WOT for long periods of time, mounting it upstream of the TB will work just fine. But when you are sitting in traffic, or have just started it back up after sitting hot for a couple minutes, the sensor in the intake will give the most accurate reading. When the engine is idling, and the throttle plate is almost closed, not much air is flowing through the intake, so the air that is in there, tends to "heat soak" (at least that is how I define it). Same when you shut the car off to pick up a six pack. The air in the intake gets much hotter than the air upstream of the TB. This is why mounting it in the intake, along with an air temperature compensation algorithm running in your ECU is important (most all do this). I've got MS datalogs from track sessions I ran with my non intercooled supercharged L28 powered track car that I can post (just need to dig them up). From these logs you can see throttle position and IAT. When the throttle plate closes, the IAT spikes to close to 270 degrees, but then drops significantly once I'm back at WOT (the throttle plate is pretty much binary during a track session: WOT, or idle). Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 25, 2007 Share Posted January 25, 2007 Actually, Pete, you are probably over pressure ratio on your supercharger when the throttle plate is closed, and the air is actually that hot! Industrial Oil-Free Screw Compressors run 260-350 degrees loaded on the first stage with 30psi interstage pressure, but when they unload, if the bypass screw around the throttle plate is not correctly adjusted the temperature SOARS instantly to well over 455F! Soon as that plate is cracked a bit, the pressure ratio across the element drops, and the temps come back down to the allowable range. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted February 2, 2007 Administrators Share Posted February 2, 2007 Ron, You are assuming that heat is conducting from the intake manifold material to the element portion of the sensor. A little more than asssuming. A heat gun pointed on the element raised temps to 160-ish. Pulling the heat gun away, the temps lingered, dropping about 1 degree per second. AS SOON as I touched the brass mount, the temperatures starting coming down semi-rapidly. Even though the testing was remedial, I feel pretty comfortable saying that the attachment surface can influence the readings. Also, air upstream of the TB has not picked up heat from traveling through the intake manifold. I agree. This is why I think every position is a compromise. Its comes down to which compromises you're willing to live with. Same when you shut the car off to pick up a six pack. The air in the intake gets much hotter than the air upstream of the TB. Agreed. But ALL of that air is gone within 2 crank revolutions. Its gone before the engine even starts. I don’t see accurately reading this condition as one of the important compromises. Although, I will concede the manifold is probably substantially hotter in that scenario and thus, the new incoming air should be slightly hotter. This is why mounting it in the intake, along with an air temperature compensation algorithm running in your ECU is important (most all do this). Understood. I would be 'with you' if it weren't for the influence that I see coming from the mount point. Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 2, 2007 Share Posted February 2, 2007 You beat me to the test (yes, I've been on the road for the past 10 days...). So it looks like the sensor element is conductively coupled to the brass body of the sensor. This sucks. Couldn't GM figure out a better thermally isolating material to put between the sensor body and the element? I thought this was the idea behind the open air sensor. So yes, if the manifold material temperature can couple into the sensor element, all bets are off. But... why don't I have problems when mounting the sensor in the intake plenum? I have never seen any type of heat soak related issue with the systems I have installed. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.