2004 Suburban Reality Check
I own a 2004 Suburban 2500 with the 8.1 gas engine, tow package with all the additional coolers for oil, power steering and transmission. It has the heavy duty 4-speed 4L85E automatic transmission, th...
Forum Discussion
mkirsch wrote:anw7405 wrote:mkirsch wrote:
Too bad GM didn't offer the Suburban with the 8.1 / Allison combination. Having that 5th gear is real nice, though I rarely ever drop below 4th as that puts the engine at maximum torque output at 65MPH.
I don't know if it's true or not but I read somewhere that it takes more torque and hp to turn the Allison than the 4l80. So an Allison would in theory have less hp and torque to the wheels.
It probably does, as it is a much larger transmission with more rotating mass. Simple physics.
The difference won't be enough that you'd feel it in the seat of your pants, and the extra gear more than makes up for it.
The lower gear in first, 3.1 vs 2.48 ally vs 4l80e is a good thing, 3rd is taller than 2nd, so not as many rpm loss when one can not hold direct.
Hp is double needed with the ally vs 3l80e, about 60 vs 30. Enough that one could very well notice it! But as noted, with better, slightly closer gear splits etc, the ally is the better trans option vs 4l80e.
The issue with the older burb bodies, is the frame will not allow the overall size of the ally vs the 4l80. You can install one, but need to do IIRC a minimum body lift of around 2". ALong with moving the crossbeam support for the transmission. Latter is easier than body lift aftermarket.
Marty
