2004 8.1 ratings

o4yukonxl · January 6, 2004

I've purchased an 04 Yukon XL with the 8.1 engine. I noticed that the 03 8.1 is rated at 20 Hp more, same with torque. Does anyone know why the change?

I love the car though. Sure beats the 5.7 1500 I traded for it.

boomer 33 · January 7, 2004

I have posted the same question on about four diffeerent boards. A few responses but none that really nailed it. The best guess was that their was an emmissions certification problem and that GM had to de-rate the motor to comply.

I tend to be more critical and believe that the 8.1 was not really consistently producing the advertised hp/torque numbers so they lowered them to actual to prevent the public relations chaos of claiming performance numbers that were not attainable. Similar to the debacle when the Mustang Cobra didn't produce the rated horespower that was advertised and Ford had to stop production until they got it fixed.

If we are lucky and it WAS de-rated because of emmissions certification, a Westers chip should bring it all back plus some, according to the post I have read on this site about the performance improvements available.

moss6 · January 17, 2004

Really can't tell much difference between our 01' and the new 04'. It seems to pull the trailer better but then it's geared 4.10 whereas the 01' was 3.73. I still need to Lyndon about upgrades to the PCM; last time we spoke he seemed to think the lower ratings were due to the PCM.

Randy

boomer 33 · January 17, 2004

Great, If you don't mind, let us know what Lyndon has to say. I really want to get the Westers and anything else "bolt on" that I could do to increase the 8.1, not that I don't get a kick out of it the way it is. A little concerned about the warranty complications though.

moss6 · January 17, 2004

One thing that I did notice that wasn't on the 01' is a welded in swelled area in the crossover exhaust tube coming from the left bank of cylinders. Futher investigation might also find this swell on the right bank. I suspect this is a pre-cat like what is always been used on the California 8.1's and could be a possible contributer to the rating reduction. Even if the pre-cat is not present on the right bank the single pre-cat would still make sense as I think that all the crankcase gasses are vented into the left bank. Removal of this pre-cat, which of course would be illegal, but might very well regain the lost power for two reasons. First the addition of any exhaust restriction will reduce flow and increase upstream pressures, and secondly if the cat is indeed only on one bank then it will have also created an inbalance of exhaust pressure from bank to bank; not good. I don't think that there are any additional sensors present so it is possible that existing sensor voltage triggers have been changed and that removal of the pre-cat might create a code event. If so Westers could reset those parameters; be can even totally negate their function for those applications classified as off-road only.

If the above is true then I would assume that the California engines have always been at the lower rating and that this change has just made all the outputs the same.

Randy

o4yukonxl · January 22, 2004

I wonder if Westers has put any 04's on the dyno. If the PCM is the problem, then it's definitely worth getting it upgraded. Has anyone switched to high flow cats?