GM-GMC: truck info, flat torque curve, allison transmisson

Question
As an employee of GM,have you heard much on the new GM diesel and allison transmisson combo coming out in 2001?
How do you think it will stack up against the powerstoke and cummins diesel?
I will be buying a new crewcab with a diesel to pull my camper and need to know so I can make the right buy.
Also,is the 6liter engine gas engine holding up. I`ve heard that it has some bugs in it. Thanks dude

Answer
Hi Todd, I should clarify, I am not an actual GM employee, but a dealership employee...just so you are not getting the wrong idea.

My personal feelings on this combo, is that it will be absolutely world class!  And here are my rationalizations:

First, Isuzu designed this diesel. It is not widely known here, but they are the world's largest manufacturer of diesel engines.  60 million (yep - million) over 60 years.  They build everything from small diesel generators to the big units used in mining.  Very big overseas, and I think that they have the knowledge to do the job right.

Secondly, Allison is THE manufacturer for heavy duty automatic transmissions.  These guys also know what this is about.  Some of the features are unbelieveable, like this tranny is smart enough to know to "brake" you when going down a large grade with a load on, so you do not have a runaway.  No more wondering if you are in the correct gear or not, for towing or hauling.  You could even set up a PTO on this bad boy!  Not many automatics can do that.  Basically, you are looking at a combination that is medium duty heavy, but in a light duty truck.  Gross Combination Weights (GCW's) up to 26,000 lbs - well into medium truck country.

Targeted ratings are 300 horsepower @ 3,100 rpm and 520 lb-ft of torque @ 1,800 rpm. Its high, flat torque curve will deliver more power across the power band than any competitor. Bosch direct-injection, common-rail fuel system. Best-in-class operating quietness and smoothness (GM had to install a lock out switch because during testing, drivers were trying to start an already running engine.)


I am told that GM is using this tranny in the Medium duty series, and a bit larger version of the Duramax as a 7.8 litre.  If one looks at the list of things on both units, you are getting medium truck performance with everything one wants in a light truck - ride, handling, ease of access.

As far as the 6.0 litre is concerned, think of this as a beefed up 350.  It has nothing to do with the 350, but the power that it makes, is somewhat similar to the kind of power that a 350 made.  It is a smaller displacement motor, that does need to rev somewhat to get the job done.  This means that you definitely go with 4.10 gears for optimum performance.  I am seeing negligible difference in mileage by going to the 4.10's.  If you have a smaller engine now, you will think the 6.0 l is awesome.  If you had a big block before (like I did) then you will want for some more power.  Also, you can only get the venerable 4L80E tranny - no Allison or 6 speed manual available with this engine. Power is 325 hp at 5,000 rpm and 370 lb-ft of torque at 4,000 rpm.  It does need to rev a bit.

Reliability has been excellent, but if you are expecting huge things out of the 6.0l, just remember that there is no replacement for displacement, and the 6.0 l works out to 366 cubic inches.  And also know that this engine is based on the LS1 Corvette engine, as are all of the new small block V8's (4800, 5300, and 6000).  So the design is not all new.

If you want power similar to the Duramax then the new big block is for you.  8.1l (496 ci) V8 with 345 HP @ 4,200 rpm and 455 lb-ft @ 3,200 rpm.  Then you get the Allison as an available option.  If I was going gas, it would be with this bad boy!

Comparison:

Horsepower
Duramax     300 @ 3100 rpm
Powerstroke 235 @ 2700 rpm
Cummins     235 @ 2500 rpm

Torque (lb-ft)
Duramax     520 @ 1800 rpm
Powerstroke 500 @ 1600 rpm
Cummins     460 @ 1600 rpm

Duramax rules!  The truck will outpull anything, and for me the best part would be that I would not need a step ladder to get into the truck, you would be able to talk softly inside the cab and be heard, and the truck will also ride better than the other guys.  Do not get me wrong, the other products are good, but these are the areas where I believe the GM truck has the strength to win.

I hope that this somewhat lengthy explanation helps in your decision making, and if I can help any further, please feel free to drop me a line.

Automotively yours,

Dean