Heres the proof as to what happens when you increase
the intake temps that the PCM thinks it sees. Tests were done using 3.91K ohms at the firewall and 3.32K ohms at the throttlebody. This gives the PCM the idea that the air heats up a little as it goes through the system, which is realistic.
Tests were performed in 70*F which is a good "practical" temperature. Lower temperatures will probably provide more power and higher temps will provide less power.
Whats it do?
. There has been much speculation that the SRT-4 PCM will increase boost at higher temperatures to make up for the fact that hot air is less dense (less air in a given volume) thus less potential for horsepower. Because our PCM shoots for a horsepower goal, it increases the boost at higher temps to make up for the less dense air. So during the summer you may see boost levels of say 14-15, but during the winter maybe only 11-12 PSI.
On most cars this wouldn't be that big of a deal, because most cars manage their fuel a little better. Our cars however run pig rich, and this is what I wanted to test. Because the PCM would see a very high intake temp it would increase the boost pressure by several PSI, but would most likely not increase the fuel at all. So the question was, did the car run rich enough that the extra air could offset the fuel and make more power while keeping safe air fuel ratios.
Why do this?
Basically this is doing the same thing as all the other boost "mods" out there. It increases the boost a couple PSI, just like a boost controller or a WGA or the other "ghetto" mods. The difference is that the PCM is doing the boosting here, so partial throttle boost stays the same and the PCM is happy without the need for map clamps. It requires two resistors which will probably cost somewhere between $0.20 and $2 depending on if you can buy individual or packs. It also takes a matter of minutes to do this.
Anything to worry about?
Yes. As I had seen when I first attempted this, the PCM lets the wastegate close very liberally at first. Which means on a stock turbo at 3-3.5K RPM you can hit 25 PSI for a split second very easily. If you ease the throttle on instead of mashing it, the turbo behaves a little better. As a result you run very lean for that small amount of time. Its not on the dyno chart below but I saw something like 17 A/F Ratio, but then dropped down to 12 across the board. This could be remedied by trying higher resistence resisters (lower simulated temps)....though it will affect the overall boost schedule. But there may be a good balance point.
So this might be a great mod for Stage 3 (which I will also dyno after I install Stage 3) because S3 also runs pig rich and the turbo is slightly bigger so the wastegate may be able to control it better. Using 2.5K resistors at both ends I was able to maintain 17 PSI all the way out...so that may be a good option for using a 50 trim on say Stage 2 and keeping full PCM drivability.
Anyways I'm sure your ready for the dyno results. Only mods are 3" BDJ's CAI, BDJ's FMIC, and the very back section of the stock exhaust removed (opens right behind rear axle). Basically mods that really shouldn't have any real benefit on a Stage 0 & stock turbo on a dyno.
As you can see....almost 250HP on a S0 car with almost no mods. The torque kept getting false readings towards the end, so that is why the torque is cut off on the base run. These runs were done 5 minutes apart. We ran baseline, turned off motor, I installed resistors, turned on car and ran 2nd dyno.
With Stage 2 to provide extra fuel and a 3" exhaust, this would probably be pretty good.
How To Do This
Take the resistor and bend the legs over so make them twice as thick. This way there will be more "bite" when you plug it into the harness. Unplug the harness from the stock IAT sensor inside the charge pipe. Now insert the resistor into the harness, pushing it in securely. You could put tape around it or cover it somehow. I just ziptied the harness to the TPS harness and let it be. I don't drive in the rain often and its been fine so far (like 6 months now).