bluenote
10-12-2002, 17:49
As far as the trailer life article...the 8100 had the 4.10 rear end vs. the Duramax's 3.73, and IIRC, the times were fairly close.
Regarding the Duramax vs. 454...I traded a 99 GMC 2500/454 in on my 01 Chevy 2500HD/Duramax. I feel the Duramax sits you back in the seat harder. For the first second or so off the line, the 454 was quicker, but after that, the Duramax is faster, IMHO. Accelerating with my 10K 5er hooked up, the Duramax wins by a landslide. These are just my unscientific observations, not based on side by side or timed results.
GMC-2002-Dmax
10-12-2002, 20:06
Had a 1997 GMC pickup before my '02.
1997 had a 454 vortec, 4L80E, 3:73's. Stock vs stock I think it would go to the 454 because of the poor low-end off the line performance of the stock duramax.
Juiced even on timing only or level 1 - Duramax all the way.
I had one and can tell you they run real good on the low end. It was rated at 290HP/415 lbs/ft torque IIRC.
......Not far from a stock D-Max and a lighter vehicle.
JMHO,
GMC :D
Trailer Life "Tow Test" article by Jeff Johnson is provided below ( only key sections on performance provied) Please excuse edit problems in article below.
Key observations from article:
o 8.1 is marginally quicker 0 to 60 wo/load (9.0 vs 9.5);
o 6.6 accelerates quicker towing;
o 8.1 had to tow at high rpms in the mountains ( 4,000 to 4500)[ relates to high mph which can be dangerous... curves, traffic,]
"...............I.Hardware Details
The test trucks were a GMC extended-cab shortbed with the 8.1-liter big block, Allison automatic and 4.10:1 axle ratio and a Chevrolet Crew Cab shortbed with the Duramax 6.6- liter turbo-diesel, Allison transmission and 3.73:1 axle. Both trucks included 4WD, the HD towing package options and, in each case, the axle ratio was the numerically highest gearing) specified for its optimum tow rating.
GM also offers a ZF six-speed manual transmission with both new engines, and 2001 2500HD and 3500 trucks with that gearbox are blessed with the same tow ratings as are the Allison automatic-equipped trucks.
Both trucks have a 22,000-pound gross combination weight rating (gcwr), and both are rated to tow conventional trailers up to 12,000 pounds with hitch weights up to 1,500 pounds. Equipped with fifth-wheel hitches and towing fifth-wheel trailers, the Crew Cab/Duramax diesel truck is rated to tow 15,100 pounds and the extended cab/Vortec big-block truck is rated at 15,500 pounds. Both trucks were fitted with factory-installed Class IV receiver hitches.
In the case of a slightly lower travel trailer tow rating, the limiting factor is hitch capacity. Up until now, most Class IV equalizing hitches, designed for the standard 2-inch receiver, were rated at 10,000 pounds trailer weight and 1,000 pounds of hitch weight. Several companies including Reese, Draw-Tite,
Putnam and Hidden Hitch have developed new Class V hitch products, and Eaz-Lift has a hitch in development; they are mostly compatible with the new GM tow ratings. The hitches available now are generally rated for 12,000 pounds trailer weight and 1,200 pounds hitch weight.
Our test trailers were a pair of similar units from CrossRoads RV of Topeka, Indiana. The trailers weighed approximately 7,000 pounds each, which wasn't enough to give the trucks a tough
workout, so we ballasted each truck and trailer to achieve a reasonable payload for each rig. All told, the Duramax diesel was towing 10,480 pounds of trailer for a combined truck, trailer and test crew weight of 17,200 pounds, and the Vortec big block was towing 10,060 pounds for a combined total of 16,240 pounds.
While both trucks have identical travel trailer tow ratings, it should be noted that this test drive was not intended as a specific head-to-head comparison between the two similar engines. Readers can draw their own conclusions about comparative performance details, but we placed a priority on showing you how these new engines performed individually rather than being pitted against each other. For that kind of test, you can look forward to big-block and diesel engine comparisons between the GM, Ford and Dodge trucks in future issues of Trailer Life magazine.
The test drive covered approximately 1,360 miles of city, free-way and two-lane state highway travel, solo and towing, and ranged from 282 feet below sea level at Badwater in Death Valley, California to elevations higher than 7,000 feet. Temperatures varied from the 60s to more than 118 degrees F during the pass through Death Valley and thereabouts in the desert.
II . On The Road
An incredibly quiet ride is delivered by both the gas- and diesel-powered trucks. Both from the standpoint of minimal wind noise and low transmission of underhood and road sounds,
the GM trucks create truly civilized driving environments.
One of our test drivers, a true diesel enthusiast, reported the Duramax was so quiet that it lost some of its diesel appeal for him. He got over that in a hurry after he'd rolled up some miles
n the odometer, as its performance more than made up for its quiet operation.
Other test drivers, accustomed as they were to older, far noisier diesels, found the Duramax a delight to operate.
Likewise, all agreed the 8.1-liter engine had a sound we're accustomed to and produced a satisfyingly healthy, but subdued, rumble outside, yet the truck is almost whisper-quiet inside under most driving conditions.
Freeway expansion joints give both trucks some fits, but that's standard for almost any heavily sprung light truck and varies a
great deal from model to model. Conventional smooth roads are taken in stride.
Cornering and steering are precise and controllable with both
trucks, and the trailers never gave us a moment's concern as we took on a wide variety of high-way conditions. Braking is
dead-ahead secure and solid, and that's the way we like it with a large load out back.
Solo, the trucks are just plain fun to drive. They leap forward and respond to the throttle aggressively. Some of our drivers
chose the Duramax over the big block for pure gutsy, seat-of-the-pants fun. As mentioned, the gas engine is very quiet, but the diesel also delivers a cab environment that does
not require occupants to shout over engine noise.
.............. All of our tow testing was done with the transmission "TOW/HAUL" mode engaged. This feature, activated by a shift-lever-mounted button, changes the transmission shift
point programming for trailering-specific needs. In effect, it raises the shift points and allows each gear to remain engaged longer to better take advantage of the engine's higher-rpm
power production before selecting the next gear.
The transmission shift timing appears to be well matched to each engine's power characteristics. The higher-revving Vortec
8.1L calls for a fast down-shift when the gas is applied for a passing maneuver, for example, while the Duramax 6.6L draws more on the diesel's lower-revving torque to implement the passing run before shifting down at a bit later time.
Each of the top four gears in the Allison has a lockup torque converter feature, so a downshift or upshift is felt as a sharp two-stage effort. First the torque converter unlocks, then the gear change takes place and the driver feels the thump of the
new shift selection locking in. There's very little waffling between gears with the Allison. It's designed to have its shift
schedule match the needs of high-demand towing, and that it does.
III. Hill Climbs
Our first sustained grade was the road north out of Baker, California, through the Dumont Dunes area with the air temperature at approximately 118 degrees F. It's approximately
a 5-percent hill and the Duramax pulled it at 55 mph @ 2,400 rpm, wide-open throttle, in fourth gear, while the 8.1 Vortec
did the hill at 60 mph @ 4,000 rpm in third gear with partial throttle application. Full throttle netted 65 mph @ 4,200 rpm
for the gas engine, but road curves instigated a slight moderation of speed.
Next came a serious 9-percent grade up Townes Pass headed west out of Death Valley via Stovepipe Wells. The air had cooled to about 102 degrees F as it was now 8:45 p.m. The
Duramax started up the hill at 54 mph @ 3,100 rpm in third gear, but sharp curves had us slow to 40 mph @ 2,400 rpm in
third gear. The Vortec gas engine maintained 40 mph @ 4,500 rpm in second gear, again, speed restricted by the curving roads.
In both truck examples, the transmission temperature gauges had climbed to approximately 240-250 degrees F during the steepest part of the hill, but both dropped back to 200 degrees
or lower once we'd topped the grade. Each gauge is positioned and calibrated such that following the general temperature
trend is easy during regular driving times, but trying to decipher
specific numbers can be difficult on a steep, winding mountain
road when the driver's full attention is called for elsewhere.
Our highest-elevation test came at Sherwin Summit near Bishop, California, which tops off at 7,000 feet elevation. The Duramax 6.6L truck and trailer climbed most of the hill at 55
mph @ 2,300 rpm in fourth gear, and crested it at 53 mph @ 2,200 rpm in fourth gear, and the Vortec 8.1L made it most of the way at 61 mph @ 4,000 rpm in third gear.
IV. Downhill Braking
Both trucks displayed impressive downhill performance while using the Allison's engine grade-braking feature, which automatically downshifts to fourth or third gear and holds in that gear selection, as needed, when descending hills. On the backside of Townes Pass, where 9 percent is the steepest part of the hill, the Duramax diesel ran away past 55 mph, then
shifted down to fourth gear, and after a kick down to third, we
maintained 44 mph @ 3,500 rpm while using the brakes a bit
due to curves for safety purposes. On a bit straighter area of
5-percent hill, we maintained 43 mph @ 3,400 rpm without any braking assistance.
According to a GM spokesman, the Allison Grade Braking feature will not allow the Duramax or Vortec engine to over-speed. If engine rpm reaches a dangerously high level, somewhere around 4,800 rpm for the diesel and 5,000 rpm for the gas engine, the transmission will automatically upshift to a higher gear and the driver would then need to use the brakes to augment the engine braking.
The Allison Grade Brake is no direct substitute for a compression or exhaust brake in a diesel, but it's nice to have
in the new GM trucks. A GM spokesman could not elaborate, but alluded to developments in the works to further assist with diesel downhill speed retardation.
The Vortec 8.1L headed down the 9-percent grade at 45 mph @ 3,700 rpm with a bit of speed increase creep, but a touch on the brakes now and then held the lash up to a realistic
speed. A 9-per-cent grade is truly a bugger of a hill, and although the Grade Brake system didn't slow us completely on these extreme hills, it was a nice feature that took a lot of load
off the vehicle brakes. Back on the 5-percent hill, the truck
maintained 45 mph @ 3,700 rpm without braking aid. The final downhill test was on the 6-percent Sherwin Grade, which starts at approximately 7,000 feet elevation. The Duramax started running away at 70 mph-plus @ 3,000 rpm in fourth gear, so a kick down to third pulled us down to 46 mph @ 3,700 rpm, where it tenuously held without any braking assistance. The Vortec gas engine held the truck near 70 mph @ 3,200 rpm in fourth gear, with the speed creeping up a little, so another brief brake application called for a shift down to third gear, where the truck held speed to 61 mph @ 4,000 rpm in third gear. It appears the diesel engine, with its higher
compression ratio, was better able to make use of the slightly thinner air at our maximum elevation point during the downhill braking test.
Fuel Economy
GM claims the new Duramax engine is approximately 19 percent more fuel efficient than its predecessor, the 6.5-liter diesel, and the 8.1 should be marginally more efficient than the earlier 7.4, even considering its greater power output. Based on our tests, the Vortec gas engine did about what we'd expect of a
big block and the Duramax diesel was great on solo mileage and average while towing.
Miles per gallon Towing Solo
8.1L gas
7.9
12.2
6.6L diesel
9.6
20.3
That 20.3-mpg solo figure for the Duramax-quipped truck is excellent, especially considering the truck was a Crew Cab 4WD. A lighter-weight conventional-cab 2WD truck could likely improve on that figure.
VII. Acceleration
There were no major surprises during the acceleration tests, in that the figures were as we'd expect for these engine-and- load combinations. The solo 0- to 60 mph runs were done at sea level, and the towing tests were performed at approximately 2,000 feet elevation. It's probable that acceleration runs at sea level would have cut a minimal amount of time from these results.
Acceleration (sec) 8.1L 6,6L
Solo 0-60
9.0 9.5
Towing 0-60 30.3 24.4
Towing 40-60 16.4 13.0
In Conclusion
GM truck fans should be more than a little enthused by theprospects offered by the new Vortec 8.1L gas and Duramax 6.6L diesel engines teamed with the new Allison transmission.
Excellent road manners, plus a quiet, smooth ride, powerful performance and reasonable-to-excellent fuel economy give
this new range of trucks something to brag about in the RV towing arena. Generous tow ratings allow for a wide range of
trailer payload options, so as of the 2001 model year, there's likely a GM truck to match most of the trailers and fifth-wheels
on the road today.
There's a new/old kid on the towing block, and it's set to stir the market. Hang on, it's going to be an interesting ride.
By Jeff Johnston
Photos: Jeff Johnston"
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