X15 Efficiency vs Performance

We have two x15 efficiency trucks, they both have 500hp. No issues yet at about 70,000 miles, no loud vibrations. They are getting about 6.5mpg pulling doubles, probably 70,000lbs usually. Don't know the gear ratio, but at 70 its about 1500rpm. Both trucks are peterbilt 567s with the set forward axle, so not the best for aerodynamics.

I don't think the mpg gap is that big from the performance to efficiency, the performance gets 5.5-6 when in a 389. So I would imagine a aero truck with the performance would get around 6.5.

 

I run for a company in a binder with a X-15 efficiency pulling a tanker & stepdeck. It has 135k on it and has had no issues yet. 500 hp, 1850 tq. It show 6.7 on the trip computer. Limited to 75 mph. I drive 70-72 on I-20 and I-45 most of the time. I have always thought it rattled too much at idle, but so far, no problems other than clutch brake. It is a 13 sp manual. I like it.

 

2018 389 with the x15 efficiency over the first 88k miles not one issue. Warm weather average 6,2 ifta down to 5.5 mpg in the colder weather. Pretty good, considering it's a car hauler. Idle only for loading and unloading. Not much difference from the paccar mx13 power wise but no check engine lights in 88k. The 2018 mx13 i had, had check engine lights on more than not. The x15 is noisy at idle but has smooth acceleration. I haven't had any issues with vibrations as of yet. I'd get another one without question. I'm impressed so far. Fingers crossed!

 

2019 567 Pete with the X15 performance series set at 565/1850. Not governed or castrated, average 5.7mpg. Pull flat, almost always grossing 75k-79k. Usually deadhead less than 100 miles per week.

 

Forgot to mention I run lots of hills(I-81 corridor daily).

 

Ordered my 2019 389 with 565/2050 performance,18 speed,3:55's,11r24.5 rubber. I pull a landoll hydraulic trailer. It pulls great and love it so far. Truck has 48 inch sleeper and is 275 wheelbase. I run it hard so only seeing 5 mpg sometime less,but what I do fuel mileage is not a real concern to me.

 

I’ve got 65k on my X-15 efficiency. No issues. No rattles. I run the 5/15/70/80/84 including all the passes. There’s a huge drop off in the average speed I can run from 36k to 44k in the box going uphill. I’m speed limited to 66mph.

No complaints. It’s a good motor and wouldn’t hesitate to recommend it. No idea on longevity though, I’m a company driver so I just hammer the thing al day long. Kinda feel bad for whomever gets it next...