86* iat timing starts to get pull regardless of coolant temp, at least everything i have points to too. 1* timing up to 0.36 g/cyl (cylinder airmass), 2* up to 0.40g/cyl, 3* up to 0.44g/cyl, 4* between 0.48 up to 0.68 g/cyl. and yes, too hot coolant timing gets pull too.

 

We do not have F-bodies and lying to the PCM as to the air temp is foolish. The hotter the air is the less molecules it has and does not burn well so faking it does not make a good burn and the O2s will tell the PCM that the AFR was wrong.
Replacing IAT sensor with a resistor is wrong for that effects how PCM sets the injector on time by seeing a IAT value much colder then what air temp really is

Reading the threads on this shows how little people understand what the PCM does and the difference in hot/bad aircharge and good cooler denser aircharge to cylinders.
The hotter the water temp is the hotter the air is in the intake manifold so anything to cool the water will be a positive to air temp quality.
GM by 150 degrees starts yanking timing so having temps above 200 is only killing off more timing and performance.

Only making one change like just commanding fans on longer or just replacing the Tstat does not cut it. The C6 has a smaller radiator then C5s have and they get hot so the C6 with also smaller engine bay will get even hotter.

Fans are only for above 30 MPH and by then natural airflow is what cools the radiator unless doing something stupid and installing something in front of it to devert and reduce that airflow.

Making part changes without tuning the PCM then is a waste of money and just forcing fans on sooner then when Tstat opens only delays then when it will open.

Myths that colder Tstats cannot rid water vapor in oil is BS, wash your hair, let it air dry does it dry without 200 plus head temp ?
Guess what the PCV does to vapors ?

Colder Tstat allows for engine to run cooler longer from a cold start and handle spikes of sudden heat increases along with then having cooler engine bay temp that then keeps the air in intake cooler.

Look at the difference from doing the proper mod changes and tune and how the temps are when stock and the real temp when sensor is in the intake manifold .

You notice that when done correctly the air temps go down while water temp only increases about 5 degree when engine is at full load where when stock the temps skyrocket effecting performance since the PCM as per GM setting is yanking timing

There is only one reason GM and other car makers run engines hotter and that is called EPA requirements.

 

Interesting post. I'm a Ford rethread trying to learn what makes the LS2tick. I have been trying to make some sense of what is going on with the intake and coolant temps with regard to timing. What temperature does the coolant have to reach in order for the PCM to pull timing. (I may have mis read the temp in a previous post and included it in my reply.) If that is the case than I have reconsider what changes I may undertake.

From your post it is apparent that the LS2 must run cooler than stock and ingest cool dense air. I would be interested in how you accomplish it. Thanks.

BTW when you mentioned sensor in the manifold you were referring to the LS1 as I did not see anything in my intake and the ECT looks like it is in the head.

 

Hey thanks for the info....... I really need to get up to speed on Chevy motors & etc

 

Here is a graph from a test I ran today. Before this recording was started I had completed a near 50 mile log for a performance test. I then let the car idle for over 5 minutes to get the IAT up over 120*. As you can see I took it for a drive at normal highway speeds to see how long it would take to get back down near ambient. The ambient temperature today was 65 degrees.

This is with a stock airbridge and stock stat with a tune.

 

Post 67 on this thread shows the table that answers your question. As you can see a LOT of timing gets pulled for warm IAT's and ECT's.

http://forums.corvetteforum.com/show....php?t=1361913

That table is for a C6 Z06 but the C5 LS2 is basically the same.

 

GM through it's modeling decided at what water and intake air temps would have a impact to engine and then built the models into the PCM.
Engine goes from open to closed loop around 160 water degrees and begins to yank timing a little to more depending on the amount of air is in cylinders as grams/cyl.
If in fact engine runs better when water temps are above 200 degrees then they would have not gone to closed loop at 160 and also allow WOT at that same temp.
We see by GM not using a metal intake manifold that they wanted cooler temps for air and not hotter

Being GM cannot assure what type of gas, weather or what elevation their calibrations sway on pulling more timing and hope the knock decay and attack rates will bring the timing back up quickly.
Being the hotter the air is the worse the cylinder burn is and being LSX engines blocks do not transmit heat out as well as with steel blocks
so anything that helps reduce overall engine temp also then lowers the air temp in the intake

Pre 2001 LS1s had the IAT sensor in airbridge near throttlebody but then moved it within the MAF as the 85 mm MAF they began using in 2001 was taken from GM trucks that had used since 1999 and the IAT was part of the MAF but that also read IAT cooler.
My point of showing the air temp in intake manifold was to show how much hotter the air is right before entering the cylinders as to what IAT reports.

To do it correctly for best cooling is higher flowing radiator, 170ish Tstat, tuning fan rotation speeds, engine oil cooler, venting hood, good CAI and not using too thick of grade of motor oil.
Doing those mods and then even in worse case like on extended dyno rums or track racing and all water, air and oil temps will rarely go over 200 water degrees and allow higher timing for WOT or reduce chance of knock that also yanks timing.

 

i am not sure for the ls7, but if i remember correctly from my service manual, at ect 140* pcm goes to close loop.

 

Depends on engine coolant startup temp, but my 00 LS2 goes to closed loop at 131* since my startup coolant temp is never below 46* here in Miami (unless I park in a meat locker!).

 

 

Since the LS2 uses port injection, the manifold isn't wet, and doesn't need to be preheated to get good fuel vaporization. Thus they were able to cheap out with a plastic manifold. GM makes the engine go closed loop as quickly as possible to help control emissions (quick light cats), but that does not mean that 160 degree coolant is ideal, or even acceptable, for WOT driving. Oil temperature is the real key to that, and when the water has only reached 160F, the oil is still too cold for maximum performance driving.

Actually, aluminum has several times the thermal conductivity of iron. In fact it is second only to copper. So an aluminum block is very good at carrying heat to the coolant and the outside air. That lowers combustion chamber temperature compared to iron blocks and iron cylinder heads. But combustion does proceed better (more completely) when the air is preheated. That's why powerplants, steel mills, etc preheat the combustion air. It increases efficiency. Keeping the coolant warmer does reduce the tendency of aluminum blocks and heads to chill the combustion chamber excessively. That's because heat flow is driven by temperature differences, same as voltage differences drive current in an electrical circuit. Keeping the coolant warmer reduces the temperature differential and slows the flow of heat out of the combustion chamber area (where it can do work) and into the coolant (where it becomes merely waste heat).

I agree with all that. Too hot is bad (detonation, less dense air charge), too cold is bad (lowers burn efficiency, dangerous to the bearings due to too cold oil, etc). Ideal is to tightly regulate the engine temperature in the 180-190 range. That's what a properly chosen thermostat, in association with adequate cooling capacity (radiator, fans, etc) does for you. Then you can tune more aggressively for best power. If your coolant temperature routinely goes more than 15 degrees (the control range) above the marked temperature of the thermostat, either you chose too cold a thermostat, or you have inadequate radiator capacity or inadequate airflow through the radiator to maintain the coolant in the temperature range where the thermostat has control authority.

 

With a 160 thermostat, I never run below 180 degrees even with the fans set to full on. With fans set, I never run above 195 either. So sounds like I'm in the sweet zone. Car runs a lot more consistently with the 160 stat and the fans set, I can promise you that.

 

If your 160 stat actually starts to open at 160, its control authority ends at 175 degrees. So you are essentially running without a thermostat, ie with no temperature control. But, as has been reported here, there seem to be so-called 160 stats being sold that actually start to open around 175 degrees, which means their control range extends up to 190 degrees. That's just about ideal.

 

Cool. I noticed that it still warms up pretty much as quick as stock. It's not important for me here in Miami (I use the heater maybe 5 times a year) but it's important to leave a thermostat in there in case I ever take a road trip north.

 

 

Thank You

Tommy

 

Brett thanks for posting the graph

Tommy