2.6% should work OK for most if not all of the locos in your list but if in doubt test first before committing. That’s what I did and decided to target 2.0% allowing for some error. So far so good.
Not mentioned, when figuring grades be sure to account for the easements into and out of the grade. Otherwise once you get building your planned 2.6% could turn out to be well over 3% in reality.
One thing you could do rather than test test test, which potentially could be a lot of work setting up the tests; you could just do like the real railroads and build to the limitations of your environment. A 2.6 % grade is relatively decent for HO trains and if anything might add some operational interest because you would be forced to deal with the limitations of the grade - which shouldn’t be too bad.
As I mentioned earlier, two powered Atlas GP7’s could pull about 20 cars up a 2.5 % grade and they were probably average for 4-axle diesels. I’d guess larger, heavier 6-axle diesels could pull a little more. Honestly 20 to 25 car trains is about the maximum length most HO modelers go with - even on larger layouts. Rob Spangler has a fairly large layout with more than one level and I recall he limits most freight trains to 20 cars. You should be fine and at worst you may have to add a little more power.
Consider this: mountain railroads such as the D&RGW had to have power heavy consists at the head end to move freight trains over the many grades, and helpers were also used on heavy trains. In the 1970’s - the “Action Road” era, D&RGW usually had 4 or 5 four-axle geeps on the head end of fairly short freight trains to keep them rushing across the system without helpers. It’s really cool to watch the Green Frog Rio Grande Odyssey - it really demonostrates the fast frequent train philosophy - no reason something like that can’t be a model for running HO trains as a justification.
Mel,
Thanks for answering about the articulateds. BTW, I sent you a pm asking about SP passenger cars in the 50’s.
Jim,
Generally agree that keeping under 3%, preferably no more than 2.5%, it’s a matter of adding power to meet the load. This works well with MU diesels.
Steam is a bit of a different thing, passenger ops sometimes even with diesels. This is because the expectation is usually a single loco. You can double-head, of course, but in most cases the prototype didn’t . You do want to avoid getting that situation going, so testing is still a very good idea for trains like that.
Despite holding the main grades to 2.5%, it took lots of mods before I could get my brass 4-car San Juan to climb them behind my brass K-28. I changed the car trucks to free-rolling Blackstones. I added weight several times to the loco, being careful to keep it in balance. I releveled/regraded the track at least three times in two different places. After about 15 years, I finally achieved my goal of getting a visually pleasing train up the grade behind the one loco I really wanted pulling it.
Hello thanks for all the good info i’ve figuired a way to get the grade to about 2.4%you really wont be able to see it as it will be a hidden ramp heading to an under layout staging area but it will have easy access for any derailments or maint.