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smitty210 · 02-14-2019, **(Subject: Driving 100 )**

I've asked dealers, and factory personal, and they are not helpful. So, tell me about these Boost Pressures, what are good and bad. I drive a Motorhome, and we've been talking about this on our forum. We have ISL450, or ISX600 engines, with 6 speed auto trans. We don't have all the gears you have to tweak boost pressures. The last hill I took, I down shifted to 5, RPMs up to 2200, and the Boost dropped from 35 to 29, not much (ISL450).

Rawze · 02-14-2019, **(Subject: Driving 100 )**

what year and model engines?

for example, you say ISX600, but it could be any of engine models --
* CM570 -- (no emissions/pre-2004)
* CM870 -- (egr only/2003-2007)
* CM871 -- (egr+dpf/2007-2011)
* CM2250 -- (egr+dpf+scr/2010-2012)
* CM2350 -- (egr+dpf+scr/2012-2017)
* X15 -- (2018+).

maybe post the engine ser#'s?

Also you should register your engine on quickserv.com so that you can get its actual specs, manuals, etc.

smorgan87 · 02-15-2019, **(Subject: Driving 100 )**

I dont understand isl450 or isx600. Which one has a problem? If ur trying to spin a 15L isx of any model @ 2200 rpm thats why the boost dropped. Its not designed to spin that fast much less pull. From factory the isx drops off prty drastic after 1500. Not familiar with the 9L isl but i cant imagine it doin much pulling at 2200rpm.

smorgan87 · 02-15-2019, **(Subject: Driving 100 )**

I am also not aware of any 6 speeds put behind an isx.

02-15-2019, **(Subject: Driving 100 )**

allison's come in 5 or 6 speed trims

in all honesty the coach world is 100% different than the truck world. They are not designed to last like a big truck and do much different things. They are designed for average consumers and drive like big cars. The trannies shift more for comfort and ease of use than engine longevity and torque curves. They dont work as hard or as long or as often than a commercial truck does. That big engine is CRAMMED in there and cummins knows full well there isnt enough airflow they just put slightly lowers cals in them and know they wont work as hard for as long and it will be somewhat OK. Ive tuned lots of them, you have to be fairly conservative and at some point the slush box trannies overcome most of the gains you get anyways.

Uni