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Old 10-07-2001, 10:45 PM   #1
Scooby Specialist
Member#: 4273
Join Date: Feb 2001
Chapter/Region: NESIC
Location: CT
2015 Taco
& 2015 Legacy Ltd.

Question Why does our cars have more cajones when the engine is cold?

Below is a quote from the part review section of i-club, notice this line: "Now the car feels like it does during the warm up period. Good linear power. "

It's my understanding that the cooler the combustion air and fuel and the closer to operating temp that the engine is, the most power will be made.

I noticed this too in my MY'01 RS 5 spd. As the car is warming up, it seems to have a whole lot more cajones (that's balls in spanish). Why is this? even with early morning cool dense air, once the car warms up, say good bye to the extra power. The only power mods i have are NGK plugs, GanzFlow, Borla Catback. Thank you.


I purchased this about 1 1/2 weeks ago and already can feel a difference in the power but not a huge difference which is to be expected. They said it takes a few weeks for the ECU to relearn with the chip. And it is relearning.

My car has always been quite slow except for when it is still warming up. During this time it has tons of power. Once it's fully warmed up the power drops a bunch. The car had no problems before the chip (or after). I have Borla headers, stock intake (due to most intakes causing a huge loss of low end on my car), and Stromung Exhaust with midpipe. Spark Plugs have always extremely clean. I have a 1999 2.5RS Auto (no turbo).

I do not have dyno figures to support what my butt dyno feels because I didn't feel like spending $300 total for a before and after dyno run. BUT!, for the last 5 months I have been trying to reach a certain speed on a onramp (going uphill no less) when I go to work. The fastest I have been able to do on this onramp is 75mph at this white mark. Well Saturday (with chip) I tried it again and I hit 80mph. (I try almost every day unless there are cars coming, then I don't) I was running the same brand of gas I always use. Part throttle response on the highway has really improved. Top end is better but not much which is to be expected with stock intake (minus snorkle thingy).

Now the car feels like it does during the warm up period. Good linear power.

I am very happy with the TC2 Auto chip. I believe results are going to vary widely per car. I was told by Kevin that I would feel a little something immediately but I didn't. It has been happening slowly just like the web site says.

I would say that if you have a completely stock car to not waste your money. But if you have all the major mods then it is worth the money. Plus, it is one step in the turbo path.

ShawnNow the car feels like it does during the warm up period. Good linear power.
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Old 10-08-2001, 01:03 AM   #2
Scooby Specialist
Member#: 1415
Join Date: May 2000
Chapter/Region: NWIC
Location: Anytown, USA
2008 IS350
'13 SantaFe


HAHA! Hey that's me!

I've come to the conclusion that as with most cars during the warm up period the car is given more gas or is running richer than it does after it has fully warmed up.

Some one once told me that it could be that more power is transferred to the rear wheels while the AWD system is cold and when it's warm the power is transferred more equally.

I'd probably still go with the top reason.

I have an old '85 F-150 with feedback carburetor. Even this thing does it. When the choke is still working during warm up there is definitely more power. After the choke has opened up completely it loses some of that power. But it's not nearly as noticeable as with the Subey.

Anybody else want to take a crack at it??
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Old 10-08-2001, 07:57 AM   #3
Member#: 2641
Join Date: Oct 2000
Location: Bethlehem, PA
2000 Impreza 2.5 RS
Dirt and Bird Poop


The reason why your car "seems" to have more power when it's cold is because the FI system operates in open loop mode until the engine is warmed up. This means that the engine management ignores input from the 02 sensors, etc. and just dumps fuel like crazy into the engine in hopes of quicker warmup. Don't forget that the 02 sensor has to be REALLY hot to work.....

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Old 10-08-2001, 12:38 PM   #4
Richard L.
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Join Date: Jul 2001
Chapter/Region: NWIC
Location: Puget Sound, WA
'00 2.5RS Coupe, AW
'93 GMC Typhoon AWD


You get more power during the warm up period because your intake charge is still cold and thus dense (more O2 molecules per given volume). To compensate for this extra air, the ECU supplies more fuel, and (more fuel + more air) = more power. This is why intercooler works because it cools down the incoming air. Another reason why the ECU supplies more fuel at start up is because gasoline doesn't evaporate easily when cold. Therefore, you need more gas to get the same amount of vapor in order to start the car and keep it running during warm up.

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Old 10-08-2001, 12:48 PM   #5
Jon [in CT]
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Join Date: Nov 2000
Chapter/Region: NESIC
Location: Connecticut, USA
02 WRX Sedan


I won't speculate about the cold-start engine management in the old Imprezas. However, for cars rated LEV, it is quite different than what is described above. Here's what the 2002 WRX does.

For the first few seconds, the ECM manages fuel injection based solely on tables. It monitors the front A/F sensor's resistance to determine its temperature. As soon as the front A/F sensor is warm enough to produce accurate A/F readings (usually within 20 seconds), the ECM switches to closed loop mode based on feedback from the front A/F sensor. However, at this point the WRX's ECM is not trying to hold the A/F ratio near stoichiometric, which would be ideal for low emissions if the catalytic converters were operating. But since the cats are not operating because they are cold, the best A/F ratio for low emissions (at least for CO and hydrocarbons) without cats is as lean as possible. To allow the engine to run even leaner than normally possible, the WRX engine has tumble generator valves, which are only used during cold start. These valves cause the air to enter the cylinders at a high velocity, creating a swirling effect which mixes the air and fuel together more thoroughly and allows a leaner mixture to ignite. After a certain length of time or when the engine coolant reaches a certain temperature, the ECM presumes the cats have warmed up enough to be efficient and the ECM switches to its normal stoichiometric closed loop regime.

How the heck did you guys decide you have more power when your engines are cold? Are you doing WOT runs with a cold engine? Crazy.
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Old 10-08-2001, 06:53 PM   #6
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2015 Taco
& 2015 Legacy Ltd.


I don't do wide open throttle runs with my car cold, that is really bad. All I know is that my car just has more power during the first 5 minutes or so. I could just feel it. Is there anyway to reprogram the ecu to make it think that the car is cold on demand? It would be like a "turbo" button. hmmm. interesting.

[edit]: dope, forgot to say thanks!
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