I was wondering, with all the talk of fuel milage and fuel prices why GM would not offer the D/A with 3.55 or even 3.43 gear ratios to improve the final drive and improve the fuel economy. It seems that for most applications, say towing under 12,000 lbs., that with the power and torque we have it would be able to turn that gear while lowering the rpms to about 2000. Or am I way off base on this thought?

I know when I went from 245 to 265, my mileage went down a little (hand calculating and accounting for the tire size) Not sure how this translates to actual gear ratio but if anything, I would rather have a little shorter gears, 1:3.95 or so would be nice. Might be enough to hold one taller tranny gear. I pull 13,500# of trailer so lighter might be a little different.

It's a HD truck. Higher gearing would probably help in fuel mileage if you were empty, but would probably hurt it's ability to do what it was built for.

For any GM design engineers out there, two speed rear end would be good. 3.05 and 3.73.

LOL that'd be awesome...

Split shifting, now that would be a nightmare for GM to try to teach the "average" driver. Be awful cool, though.

HEY! How about a 13 speed w/ Double overdrive http://www.dieselplace.com/forum/smileys/smiley2.gif Like I use in my "Big Truck" Kenworth http://www.dieselplace.com/forum/smileys/smiley36.gif

Now lets not over do it.http://www.dieselplace.com/forum/smileys/smiley1.gif

Never thought of the 2 speed rears; our old farm trucks had them. With all the other sensors they have in these things, they could probably make it an automatic system. Also, what about the "power on demand" system they were using in the Cadillacs that shut down some cylinders when not needed? Would that work in a Duramax??

Seems like a second overdrive (6th gear) in the Allison would be the way to go, and it would have a 6th gear lockout when towing.


JP

Now if we could only get some GM engineers to take a look at the suggestions. Keep 'em coming.

Maybe we should start a thread, to help out the GM engineers.
Then foward the URL to them. Let them know what the consumer
wants. Enginneers are book smart, practical dumb (in my
experiences)

Gee Max! You went out on a limb with that remark. I see an engineer coming carrying a chain saw. Evidently you haven't worked around many engineers. I think the GM engineers did their homework very well on my truck. I would bet a $100 you just p***ed some of our forum engineers off. Later! Frank Edited by: Frank Blum

You could approach the same principle as a 2 speed rear end using a Gear Vendors auxillary transmission. They have solutions for 2wd and 4wd (only works when running in 2wd). I didn't see anything on their site for the new trucks, but they may be working on it.

My 315's give me an effective 3.30 ish. I lost 1 to 1.5 mpg. Granted it sits 4.5" higher and tires weigh a ton more. It really likes 2200 rpm and at 70 I'm only pulling 2000. On the flat it pulls my trailer no problem. I like it with the 6spd because 5th tops out higher. The one 6% hill I pull my trailer up I drop to 5th at the bottom and let-R-roll (stock).

Any truth that GM is going to "activate" the Ally's 6th gear for 06?

Sorry Frank. Been my past experience in industry.



Seeing your profile, you of all people should be able to relate.

Max I can relate but I also have worked with some very good ones that have got my butt out of the ringer on a few jobs. We had over 300 engineers at our facility. My son is a ME manager. Designs water cutter robots for the Space Shuttle booster washout program. He worked as a trades helper in several crafts before getting his degree. Later! Frank