Check out this datalog

[chip/exhaust]

Have a 2005 Cobalt ss/sc that's way down on power. Car ran great for months, came in last week and dynoed 50 wheel horsepower less all of a sudden. Vehicle passed compression, leak-down and injector flow testing. Tune is still where I want it on the timing/af.
So far:
-Exhaust has been upgraded to a lt header and catless 3"
-Spark plugs have been switched for 1 heat range colder plugs
-Supercharger has been verified to produce the same 15.5 psi
-Torque is only off by 10-15 ft. lbs.
-IAT's appear to be within range and heat exchanger is flowing coolant
-Hp curve is significantly affected being 5-19% lower at all rpms

[BlackSS/SC]

Looks to me like you're not logging knock because you should see a number beside Total KR. Your timing was going up and down during the WOT run so I'd say log KR and fix it in your tune and that could be your issue.

[chip/exhaust]

Saga continues. Here's the log. I've removed areas of kr, the car is still way down on power. IATs are seeing the 140s, but power is waay off everywhere. Any suggestions?

[Denny]

Saga continues. Here's the log. I've removed areas of kr, the car is still way down on power. IATs are seeing the 140s, but power is waay off everywhere. Any suggestions?

Your commanding almost 12.0 AFR at WOT....thats kind of lean since real AFR is almost always higher .5 or so.

Next you hit 20.5 degree of timing when you got knock while at WOT....what kind of Gas are you running? You need more the 95 octane to run that amount of timing.

I'm at the same point as you running max timing 21 degree I drop a can of LUCAS octane booster just to see what was going to happen and presto no knock with 21 degree of timing.

So Im going to run Meth/water injection soon so no more knock at 21 degree of timing.... but for now I run more octane since I love the power the car makes at 20+ of timing.

[chip/exhaust]

AFR is reading clean at 11.8-12 on my wb. I've corrected the KR area already, I'm wondering if anyone can see any reason in the datalog why the vehicle is down approximately 50 wheel hp.

[spyhunter]

did you go back to the same dyno place? What was the ambient temperature outside compared from your first dyno to this hp drop recently on the dyno?

DOES THE CAR FEEL ANY DIFFERENT?

[Julex]

Even though you passed a compression test doesn't mean you don't have a blown headgasket, which could only be losing compression at higher rpms with higher heat. I think that's what mine is doing passed all tests, it's either my Head gasket or a piston ring. The car runs great but once I step on it after 3-4k it feels almost boggy. I lost .5 on my 1/4 mile time also. But it could be my clutch is totally gone, since when we tried installing the faulty CM clutch the stock one only had the grooves where the pads were haha. Yea pretty bad, that's my hope is that it's that.. Good luck!

[spyhunter]

AFR is reading clean at 11.8-12 on my wb. I've corrected the KR area already, I'm wondering if anyone can see any reason in the datalog why the vehicle is down approximately 50 wheel hp.

Again how does the car drive. Is it driving any different? I've seen cars, for example, consistant 12.1's, and went with a friend tuning ont he same dyno before one event to make sure everything checks out, then dyno again before an event a week later. RAN the same times, but the dynos were completely off by 20-30hp. Car didn't feel any different, car ran the same times at the track, just the dyno decided to, "do its own thing".