[ob_1jr]

Either of the 2 are going to be pretty quiet. I know walking by either of the 2 it is hard to hear them compaired to my LB7. As far as having problems changing the 5 speed to a six....I haven't heard of any problems and it is pretty easy. I wouldn't however install it on a truck that has a programmer and stock tranny. It isn't recommended used with power adders unless you have one of the tranny beef-up kits like the one from suncoast.

 

[ob_1jr]

So the previous 5 speed Allison can handle more power than the new 6 spd?

No, I am talking about an upgrade to the 5 speed to make it a 6 speed. I thought that is what you were asking about. check out suncoast's site. I am pretty sure that they give out about the same when it comes to power adders. Actually the six speed probably takes less to limp since you start out with more power to begin with.

 

[ob_1jr]

Injector design and some internals. Most the sound you hear from the diesel engine is from the injectors. I believe that the compression ratio was lowered to 16.8:1 vs 17.5:1 on the earlier engines. I believe those are the numbers I remember reading. The new engines are almost as quiet as a gas engine at idle.