So what's up with the air pump on the '04+ XRS/GT?

[Mase]

Broken off from another thread...Quote, originally posted by Psychobroker »Not true. '03 (maybe '04's too) GTs came without the smog pump and were rated at 180HP (crank), whereas the '04/05's lost power due to the pump and are now rated at 173 HP (crank).There's no proof that the air pump on the '04+ 2zz's is responsible for any power loss. I've seen numerous dyno's between the '03s and '04s and the peak hp is identical. The only difference is the '04s have an earlier peaking torque curve. The 180/173hp listing is all about marketing...nothing else. The air pump is often the scapegoat for supposed power loss since it is the only most obvious addition to the newer models.Quote, originally posted by Psychobroker »Are these dynos available? There's a few threads around here pointing out the smog pump as the culprit. Why would GM simply underrate their car from one model year to the next? That seems like marketing suicide to me...please explain to me how underrating your top model (Vibe or Trix) would assist in marketing? These dyno's are posted somehwere on MO.com but I can't access them from work right now. Talk to Redliner9k over there, he's been the primary tester of all model XRS's. He has found that the 04's, because of their better torque curve, are actually marginally faster than 03's. He has yet to test up against an 05.I can't see how the air pump would affect horsepower. It's an external system to the engine. The only time it is ever on is for 2 minutes during a cold start up. The only change to the 04/05 engine is at the head. There are 4 TINY ports drilled above the exhaust manifold that allow the air from the pump to inject into the exhaust gas. I don't think that tiny change can rob 7hp. Has anyone ever wondered if the original 180hp rating on the 03's is actually overrated and that it was corrected for the 04/05 models?

[Psychobroker]

Quote »Has anyone ever wondered if the original 180hp rating on the 03's is actually overrated and that it was corrected for the 04/05 models?You may have hit the nail on the head! 180hp looks better on paper than 173...

[MoonDogg]

Good point.. I too wondered the same thing...

[Mase]

Some dyno sheets:2003 XRS dyno2004 XRS dyno

[ToolGuy]

I have an air pump on my Vette for cold start up warm up emissions and NO it does not hinder performance and cannot be eliminated, at least on my car. Or if it can you would have to go through a lot of BS to do it. Right, once it does its job, it is done.

[goodvibe]

The air pump's just part of a pollution re-do on 04s and later that included reprogramming the ecu for added midrange torque, a higher lift point and lower emissions. I've seen the curves on the 03 vs 04 and even though they seem to make the same power, I still believe an 03 will ussually make more at peak but that it's really not that important. After all, Toyota Canada compensated early 04 owners that were told their cars made 180hp and apperantly didn't. 03s were never questioned. There's a lot more to go fast than peak power. I don't think the power difference is a big deal as a stock 04 seems to make more power up to 6k. The biggest difference is that there is no way to stay in lift on shifts. Maybe Toyota just wanted to remove the temptation of banging gears or it's just spewing to much unburned gas in lower lift with all that overlap. I would be just as happy with a stock early 04(6200-lift) as an 03, maybe happier as I greatly appreciate drivability. That's why I have a Unichip and don't have an intake. I suspect a Unichip won't help a stock 04 as much as my 03 since Toyota did a better tune on the 04 to begin with. I just wish they would stop raisng lift.