I've seen a few references describing how the stock ECU can reduce power when the engine gets hot, like during extended track sessions.

I've also heard that aftermarket ECU's can address this issue.

Does anyone have any more info on how/when this power reduction occurs, how you can tell if you are experiencing the power reduction, and most importantly, a grass-roots method of "fooling" the computer to avoid the power loss without adding a $1,000 Mugen ECU?

Since it has been said that it is retarding timing in response to higher temperatures I bought the Mugen thermostat and higher pressure radiator cap. May not be enough when air temps go up but it was all I could do cheaply.

Perhaps a more accurate water temp gauge would help in figuiring this out...

This SPA one would be nice, http://www.grahamgoode.com/dg104.gif but a quick google search shows many options, including a cheapo j.c. whitney one http://a235.g.akamai.net/f/235/2654/...ache/I2111.giffor $35.

I guess 3-bars of temperature really covers quite a large range?

The ECU retards the timing when it senses knock. Knock is caused (in part) by high temperatures. If you do not compensate for it, pinging and detonation occur and you damage your motor.

The moral of the story is - don't f*ck with your knock sensor, it's your friend.

I think that the loss in power occurs before there is any knock (ping). ECU playing it safe for the engine. The real culprit is temps, either coolant or air.

When the ignition is retarded because of the knock sensor their is a sharp drop in power all of a sudden. What we found is that the car will pull strongly but the reading of peak power will start diminishing by 1 or 2 WHP after every pull. The more dyno runs, one after the other, we did the more peak power we lost. We measured up to 6-8 WHP less.

The Mugen ECU Address the issue but at $1,500, and you loose the theft immobilizer, is a pretty expensive mod. You do get to keep your stock ECU.

Fooling sensors? I really don't have a clue to which ones are the ones that the ECU uses for lowering the power through less timing. I would guess that it could be a combination of the air temperature sensor and coolant temperature sensor.

My mod idea was an in-line resistor to the coolant temp sensor to make the ECU "think" the car is running cooler than it is... Actually a somewhat common mod on other cars.

Of course you don't want to drive the engine into the ping-zone, but the first thing I wanted to do was try and verify this power loss...

Letting engine running full force at high temperature is without a doubt disastrous for the engine and stock ECU will indeed cut in to prevent that from happening.
Mugen ECU will solve this problem and let you take a risk by running the car full force at any temperature. But you would be very foolish to run your car without any regard for safety of your engine that is why Mugen absolutely advices you to invest on the accurate temperature gauge to closely monitor the engine when running with Mugen ECU.
If you want to run your engine cooler is your absolute priority, investing on the bigger radiator would be only your prudent option. Price around $800-$1500 depending on the manufacturer and the material used. Aluminum ones are the ones that are usually priced $1200-$1500.
But Mugen ECU's another attractive selling point is the slight reprogramming to solve the bog problem and give you nice boost on the low-end. Just hearing from me would be hard for you to understand but one test drive and you will understand how better it makes it.

This may work but you will probably have to do the same to the air temp sensor. You will have to do it on a dyno to verify the results and probably use a variable resistance (potentiomenter) to find the perfect setting (ohms) and then just buy fix resistances and put them in line for a cleaner look.

I have used used an alcohol injection system on my previous Eclipse turbo to combat detonation and high temps. Any thoughts on using an alcohol or alcohol/water injection set-up on the S to help with high temps.

without knowing exactly how the ECU is programmed its hard to say which sensor tells the engine to cut power, I would guess an air sensor rather than coolant, coolant tells you how hard the engine is working and the air sensor would better predict detonation.

When I have felt the power cut (which is substantial) the engine had not been working hard, and was within normal operating temp, but it was in the 90*F range ambient.

Higher compression engines are more likely to change output with regard to temp anyway.

Sure water injection would help, but not in this case with the ECU cutting back, run the mugen, and raise compression, and without higher octane gas you would need it.

If changes are made to the sensors, It would be wise to monitor the vitals closely.