Ductape wrote:
Backstory- we're in the market for a short coach, less than 36 feet. It's our preference (due to the types of parks we enjoy). Likely a Newmar Ventana or Ventana LE or Tiffen RED. We'll pull a large toad. Perhaps new, but we'll also consider going back a few years, but not before DEF engines.
I dislike a powertrain that's maxed out on torque and has to shift gears too often. Defeats the whole purpose of a diesel so to speak. And I've operated some trucks like that.
The real technical stuff: Most coaches in this range are built with the Allison 2000 series trans, a few have the 3000 Allison. The smaller transmission has limited torque handling capability and is used with the ISB 300 or 340, with peak torque ratings of 600 to 700. The Allison 3000 enables use of the ISB 360 which is 800 lb-ft torque. Which seems like not much difference, right?
But here's the thing; the 2000 series requires the use of torque managed engines, which limit the torque when shifting (not a bad thing) and also the torque in certain gears (and this is my concern). The 2000 series trans allows up to 700 lb-ft in gears 3-5. In other conditions it's limited to 575 lb-ft. Limitations on the Allison 3000 are not a concern with the ISB, as the trans can handle 1250 lb-ft and torque management is not required.
So... it would appear that the ISB360/Allison 3000 combo can draw on all 800 lb-ft of torque to maintain speed on a grade in any gear, whereas the ISB340/Allison 2500 by comparison can only use 575 lb-ft in 6th gear. That sounds like a recipe for easily dropping out of 6th with the smaller transmission. But does the real world experience match?
Thanks for your patience in reading my dissertation, and I appreciate your feedback.
Rule of the thumb, without all the technicalities, is to have around 10HP per foot, which provides a decent amount of torque and is usually more than sufficient to handle a fairly heavy toad as well. It ends up being with the amount of weight you're trying to move, per the engine size.
You stated under 36ft, so story short, I'm most sure if you get a 340HP power plant in a 34ft coach, you're good to go as well or better than many. Anything close, should serve you well, also.
With our almost 41ft and grossing a little less than 37K lbs. including the toad, we spend most of our time in 6th gear, over all kinds of terrain.
