What confusion? Here are your words: "Power decreases by 1% for each 11*F increase in inlet air temps...". Does that not refer to the air temp at the point where the inlet valves open? And is that temp not related to (a) the ambient temp and (b) the current coolant temp?

My point is that the inability of this engine compartment to shed heat quickly enough means that at high ambient temps like 108 F, heatsoak might cause the IAT2 to even exceed the coolant temp.

If not, how do you explain estimated power losses of 50 - 100 HP? Surely not as just being due to "butt-dyno errors".

 

You're mixing up and overlooking things. IAT will be the 108F, unaffected by heatsoak because the air hasn't yet got into the engine bay more than a tiny amount and is moving. The engine coolant doesn't go near it, but the separate SC coolant does. We're debating what happens under boost so the air has been compressed and then cooled by the ICs. IAT2 tells the PCM what it needs to know and fuelling & timing etc are then set. I don't see how engine heatsoak is relevant in this scenario. If it is, it looks like it would be minor.

To me the power loss is subjective/unknown (no dyno or the like) but the presence of a P0191 makes it pointless to do other than fix the car. Which the owner is trying to do.

 

Some good points raised!!

I think my code 0191 needs to be fixed before I can know if the car was getting enough fuel. I started another thread on my 0191 code. The car is losing power now.
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I think we've discussed this before- but you're again grossly overestimating the amount of heat gained by the air as it passes through the inlet tract. If I remember correctly, a manufacturer of inlets came forward with actual measurements that were in the region of 1 or 2 degrees C or F, I've forgotten.

There essentially is no 'heatsoak' condition -the air is constantly moving with enough volume and velocity that energy transfer from the engine (which is at a constant temperature as controlled by the coolant and thermostat) is virtually zero.

 

I agree with both Mikey and JagV8, "heat-soak" is the wrong term to be using here, as it actually refers to heat build-up in the coolant after the engine has been shut down, and has been blamed for some under-hood fires.

The STR problem is more one of overheating, because the coolant system gets little or no help from under-hood air circulation in removing heat from this high-performance engine. So, everything gets hotter, including IAT2.

No doubt that something is causing the power loss, and that something is temperature-related. Maybe the next person doing a dyno run can turn the fan off - isn't the point of those fans to improve air circulation?

 

Robinb - The point of the fans is to force air through the radiators. The SC rad gets better cooling as it is before the engine one. The engine only wants enough cooling to get the engine coolant as close to the max engine operating temp as possible. The thermostat is there to make that happen. For clarity, that coolant circuit is not the SC one, which does not need and has not got a thermostat. It wants as much cooling as possible and it can be considerably cooler than the engine circuit.

There isn't heatsoak to the SC circuit or the intake air. There is potentially heat build up from a cold car, which in the example would start at 108F, in the sense that hard boosting will heat the SC coolant circuit if the SC rad can't get rid of all the extra heat, either instantaneously or over a longer period. No one seems to be measuring the SC coolant temps so it is just a guess how well the SC rad can keep up.

 

I had a similar problem and replaced my thermostat. I'm still amazed at the difference a year later. A couple of weeks ago on a 104F day my STR still acted like a juvenile delinquent on crack...

 

Yes I have also changed the thermostat a while back.

The heat soak is always worse if the car has been driven a good bit. As has been posted you are heat soaking the IC circuit coolant and reducing it's ability to lower the intake charge temperature. Then the IAT2 sees a higher intake temp after the SC and pulls timing out reducing power.

Working on fixing my 0191 code first!
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JagV8 you are right!

My 2005 does have a return less fuel system. I got confused because when I changed the fuel filter I had some other fuel lines running to the back of the car. Maybe for some kind of vapor control??
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Maybe for the EVAP feature?

 

I think so?

Sorry for the incorrect information.
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No worries! These beasts are pretty complicated.