Unexpected but very nice surprise from DC software - quiter car

[PhoenixGTS]

[quieter car - sorry for typo] I normally run a Mopar High Performance PCM (Code ending in 5007) on my 1998 GTS. I have a spare computer so I sent it off to DC Performance to have them write me some software. I did before dyno testing to give them a baseline (I will try and get back to the dyno this week so I can do a "before and after" post) but made Chris's job difficult by making the before run with the Mopar PCM then sending him a different computer. In any event, I received the computer back yesterday and put it in after work. Went for a test ride and there is an unexpected but very happy side effect from the new programming: the car is significantly quieter. Since it was chilly out I thought at first it must be that I had the windows up compared to having them down the last time I drove the car, so toward the end of my test drive I rolled a window down and drove next to a wall so the sound would bounce back to me. The car is definitely quieter at WOT. What do you think? Is this maybe because the timing is more advanced and the combustion is over before the exhaust valve opens as opposed to some of the explosion leaking out before? I've always hated my car being so loud so this is great. It feels slower so let's hope my SOTP dyno is wrong. Maybe my mind is thinking it must be slower because it is quieter!

 

[Tom F&L GoR]

Richer mixture can also burn slower, so that might limit the sharpness of the sound.

 

[plumcrazy]

richer and then cats clogged. go stand behind them and feel how far away you can feel the exhaust. let us know. you SHOULD feel the exhaust about 36" or so off the tips.

been there done that

 

[PhoenixGTS]

go stand behind them and feel how far away you can feel the exhaust. let us know. you SHOULD feel the exhaust about 36" or so off the tips

I'll do better than that. They'll stick the A/F mixture probe in during the dyno run. Interesting concept Tom brings up. If he is correct it should run cooler also but so far it does not seem to be much different - of course we have had very cool temps here so my "testing" is skewed.

 

[plumcrazy]

please do this BEFORE any dyno runs !!! if clogged on a dyno, it can and most likely will go BOOM.

dont ask me how i know this.....

 

[PhoenixGTS]

please do this BEFORE any dyno runs !!! if clogged on a dyno, it can and most likely will go BOOM.

It was quieter instantly - as soon as I started it with the new PCM - so it is not from clogged cats. Don't even think I have driven far enough to hurt the cats even if there was a problem with the mixture being too rich.

 

[plumcrazy]

did ya start it yet and see how far back you can feel the pressure from the exhaust ?

 

[PhoenixGTS]

did ya start it yet and see how far back you can feel the pressure from the exhaust ?

Finally drove the car again today, and just so that plumcrazy can sleep well at night I got out and did the "exhaust check." Nice strong puffs out of both sides are felt at a distance of three feet. In the cold morning air the car was blowing the rear tires off so not much SOTP testing. Car is bucking at low RPM but it has done that in the past. I'll tweak the throttle body alignment this weekend and that should take care of buck. Still smoother. Still quieter.

 

[Tom F&L GoR]

Too late to get a "before" data point, but what about plug color?

 

[PhoenixGTS]

Richer mixture can also burn slower, so that might limit the sharpness of the sound.

Follow up dyno runs today said your guess was incorrect Tom. The A/F mixture went from 12:1 to 13:1 (a LOT less black smoke). I'll post results this weekend but bottom line is going from #5007 Mopar PCM to DC programming got me 10 foot pounds of torque to the wheels between 4,250 -4,500 rpm to the wheels and a corresponding 5 or so horsepower. Probably a gain of half that between 3,000 - 3,250 rpm. Drivability is smoother and it is effected less by intake temps (subsequent runs do not lose as much power as before). I'll run it by Chris at DC and see if he wants to tweak it (more timing maybe?). Charts later.

Here is the before horsepower curve with the air/fuel mixture. The Mopar PCM is trying for 12:1 but not doing a great job,

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The after chart shows that DC did a great job of stabilizing the A/F mixture around 13:1. Don't mind the odd squiggle. The operator forgot to turn the A/F sensor off and it looped back and started again.

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