When does a consist needs 2+ Legacy Locos

Hard to estimate as you are using different companies products. Its all a function of rolling resistance but I would say 7 cars for one engine with a pair a Mabuchi RS385s is about right. If they were all Lionel cars, maybe a few more.

Pete

Based on my own experience, 7 scale passenger cars with incandescent lighting is practically the limit for a single Legacy diesel with two can motors. The specific example I am thinking of is a 7 car set of Lionel 21" aluminum cars, which are not light but roll relatively freely. I've never measured the amp draw of this consist but non-LED lighting will consume a lot more power than more recent LED-equipped cars. The other problem is traction, of course, and the traction tires of the powered A unit I use with this have had to be replaced after a few hours of running time. They were not problematic to begin with.

An A-B-A Legacy diesel set I have with two powered units has never had any problem pulling as many as 12 scale passenger cars, some with LEDs and some not.

Rolling resistance is the name of the game. I know the newer Lionel 21” cars are stupid heavy I run 8 I think and that is starting to push the limits on one locomotive with the 3% grades on our club layout (should’ve never let those get so steep) but on level track it’s doable

Don't forget the visual effects of creating a long hauler, MU's can be very distinctive. For my layout I love the MU setup and build consists of 12-14 units.  On some consists I use a powered helper in the middle of the consist.  It prevents string lining on the curves. There is no question that eight passenger cars would not only look good and if you have any +2% grades would help the whole train run smoothly.

You will see in this video how steep my grade is and how tight the curves are.  But it works!!

@Wood I think that consist looks great!  As does your layout!!  Thanks for sharing that! I have nothing against, whether aesthetically, resource wise or in principal, running MUs.

the main reason for this post is due to the below occurrences:

1.) I tried running the above consist with a Phase 3 Legacy F40PH, and that loco struggled. So I added a second one and it worked much better

2.) My recently acquired HHP-8(separate sale with TMCC, err cruise, sounds, cab #664) general lack of pulling power for consists with more than four 21” coaches. However, from what I have read, that engine is light and adding some weight can add to the pulling power

@StevefromPA posted:

@Wood I think that consist looks great!  As does your layout!!  Thanks for sharing that! I have nothing against, whether aesthetically, resource wise or in principal, running MUs.

the main reason for this post is due to the below occurrences:

1.) I tried running the above consist with a Phase 3 Legacy F40PH, and that loco struggled. So I added a second one and it worked much better

2.) My recently acquired HHP-8(separate sale with TMCC, err cruise, sounds, cab #664) general lack of pulling power for consists with more than four 21” coaches. However, from what I have read, that engine is light and adding some weight can add to the pulling power

@StevefromPA

Thanks for the nice comments. I understood what you were asking. My post was to push the idea of MU's.

I have both the F40PH and the HHP8. The F40PH is a pretty good running engine and I pull 6 16" KLine bombardier passenger cars. It will not pull my Superliners. The HHP8 is very light and weak. It can only pull 4 of the KLine cars.

There is no formula. Every engine series is different. F40PH vs HHP8. I think you just have to run the engines and asses which ones are capable of hauling the cars. If you have problems add another engine.

PS. With 2 180 bricks you have plenty of power.