8.1 HP ?

f7_ditch_jumper · August 24, 2003

Ok does any one know why the 8.1 lost HP? It was 340, now i see it at 330 or 320 depending what i read. What happen?

R Dogg 56 · August 24, 2003

We're still investigating it.

HendyPhoto · August 24, 2003

They are using that to sell more diesels I bet. OR they are telling you the HP at 3000 RPM's, not 4500.

f7_ditch_jumper · August 25, 2003

The RPM theory wont work. Both rated @ 4200

CMNTMXR81 · August 26, 2003

Perhaps C.A.F.E. requirements that GM is changing their "rated" number so as not to get penalized.

422 SS · August 26, 2003

I seriously doubt anyone will notice the loss of 10-20 hp in a 6500lb truck.I don't know why they would go backwards though.

HendyPhoto · August 26, 2003

How much worse is fuel mileage and horsepower when you have on the air conditioning (8.1 and Dmax)? Anybody know?

BlackSilver · August 26, 2003

How much worse is fuel mileage and horsepower when you have on the air conditioning (8.1 and Dmax)?

Obviously the engine horsepower remains the same.

With these strong engines, the modest load of the A/C compressor probably causes a neglible drop in MPG which could only be measured under laboratory conditions.

422 SS · August 26, 2003

I don't have any hard evidence but I know mileage suffers in town with the air on in any vehicle.On the freeway a vehicle with a decently powerful engine should get better mileage with the air on and windows up.In my camaro I would see a 3-4mpg improvement on the freeway with the windows up and A/C on.With the windows down the aero drag would increase fuel consumption.I have never done a comparison with my trucks though.The newer A/C compressors don't drain as much power.

HendyPhoto · August 26, 2003

Thanks for the fast reply, I was just wondering because yesterday I was pulling my 6500 pound boat up a 7% grade and when I turned off my AC, I started hauling-A!!! So I was just curious as to why the AC drains so much power!

CMNTMXR81 · August 26, 2003

Did you have the system closed (the button for recirculation)? That'll add more load. And of course, the higher the temp, humidity and dewpoint, the more the compressor has to work to overcome it.

awdvkd · August 26, 2003

All having the reciculation on does is close the outside vent to keep it from drawing fresh air. It also increases the fan speed. How does that increase load on the compressor. If anything it would increase the load on the alternator due to increase of fan speed. A compressor works the same all the time, it either off or on. I have never noticed any difference in MPG with or without the ac on. I can't even feel a difference when you turn it off or on.

BlackSilver · August 26, 2003

yesterday I was pulling my 6500 pound boat up a 7% grade and when I turned off my AC, I started hauling-A!!!

If you noticed a significant difference in engine power when you turned off your A/C then you have a problem somewhere. Your 8.1 shouldn't even notice it's there, especially if it's higher in the RPM curve as it'd be pulling on a grade.

HendyPhoto · August 26, 2003

Do you think it's a leak or something? I will take it in and have it checked out. I was pulling up the hill doing 50-55, so its not like its really bogged, but I can tell a differrence when I turn off the AC. It seems to gain when the fan turns off, when it gets hot, the fan kicks in and I lose some power.

Before I go get it checked I would like to go in there with a few educated guesses, so they dont think I am an IDIOT!!! they seem to be more helpful if you know some things, and can tell them what the problem may be!! If not, there is a BIG chance they will tell me "Oh it's nothing, thats normal"

I HATE THAT!!!!!!!!!!!!!!!!!!!!!!

CMNTMXR81 · August 26, 2003

All having the reciculation on does is close the outside vent to keep it from drawing fresh air. It also increases the fan speed. How does that increase load on the compressor. If anything it would increase the load on the alternator due to increase of fan speed. A compressor works the same all the time, it either off or on. I have never noticed any difference in MPG with or without the ac on. I can't even feel a difference when you turn it off or on.

A) More load on the alternator

B) Due to higher humidity and dewpoints the compressor has to work more in the "on" position to compensate.

If you ever watch the compressor while you have the hood open and the A/C on, you'll notice the compressor clutch engages and drives the compressor for 30 seconds to a minute, disengages for a few seconds, then repeats the process. A higher temperature, humidity, and dewpoint may keep it engaged for longer periods of time adding a more continous load on the engine. Then there's the additional load on the alternator. You may not think it's a lot, but when all added together it can drag on a motor regardless of it's size. A wore compressor can add to the problem even more exponentially.