Test Drive: Cummins X12 Diesel Engine Version 2.0

Cummins’ new X12 engine is slated to hit the street sometime early this year, probably shortly after its formal launch in February or March. The engine was introduced in August 2016, and I had a short drive with it then around the 7-mile loop track at the Transportation Research Center in East Liberty, Ohio. It wasn’t much of an opportunity to get to know the engine, but it whet my appetite. Cummins invited me to drive the new X12 this past November on a longer real-world route, starting from the plant in Jamestown, New York, where the X12 is to be built.

 The X12 has a displacement of 11.4 liters, which, according to conventional mathematical rounding principles, should have caused the engine to be named X11. However, the engine punches above its weight, and to call it X11 would have diminished some of its brightest attributes. Tipping the scales at just 2,050 pounds, it has the highest power-to-weight ratio of any heavy-duty engine from 10 liters to 16 liters in size. It’s lighter than any 11-liter block on the market (albeit subject to interpretation on how “dry weight” is determined). And its published ratings put it squarely in 13-liter to 15-liter territory for torque and horsepower.

Under the hood

Development on the X12 began in 2013 in close collaboration China’s Beiqi Foton Motor Co. There it was known as the ISG. The version of the engine we’ll see here in the next month or so has been almost completely re-engineered. Cummins tells me that close to 90% of the engine saw some re-engineering to ready it for North America.

On the road

For this test drive in a van trailer grossing 61,100 pounds, I ran about 90 miles on a nice mix of Interstate and flat and hilly two-lane roads. I headed west on I-86 from the plant in Lakewood to Northeast Pennsylvania, where I flipped back eastward on I-90. I got onto New York State Route 5 at Ripley, headed east to Westfield, and then back south to the plant on S.R. 394 and 430. It’s a great route to test an engine like this, because it’s exactly the kind of terrain on which it will operate in real life.

The engine was installed in a Freightliner Cascadia daycab with a manual transmission. I opted for the manual because it gave me a better feel for what the engine could do, unaffected by an automated transmission with ideas of its own. It was a 10-speed Eaton manual with a 0.78:1 OD ratio, 3.58:1 rears and 11R22.5 tires — a typical spec for a regional/P&D operation where the X12 might find itself.

We’ll learn more about it when it’s formally introduced, but based on what we know about the ISG, the X12 has about half the number of parts found on other diesel engines. It uses a sculpted block design for greater rigidity and less resonant noise. The block was engineered to remove as much metal as possible to reduce weight without sacrificing structural integrity. Several composite components, such as the rocker cover and oil pan, also help reduce overall weight. It features optimized intake and exhaust ports for easier breathing, and coolant and oil galleries were engineered for easier flow with less pumping effort. It uses the XPI high-pressure injection system and a Cummins-designed integrated engine brake that delivers up to 50% more engine braking horsepower than traditional engine brakes, the company says.

I have also been told that the X12 will be available with Cummins’ full suite of electronic fuel efficiency and operational enhancements, such as Adept (SmartTorque2, SmartCoast, predictive cruise), Load Based Speed Control, and Connected Diagnostics. It will also use Cummins’ Single Module aftertreatment system.

This engine was rated at 455 hp/1,700 lb-ft. The power curves indicate peak torque extends from 1,000 rpm all the way up to 1,400, while the peak horsepower of 455 is available from 1,400 to 1,900 rpm, which is a dream configuration. You have a 400-rpm range for peak torque, which gave me a 15 mph range on the Interstate in top gear where I was cruising at peak torque, from 50 to 65 mph. At 65, I was running 1,400 rpm. I was down to 1,000 at 50 mph, which is a bit low for a hilly road, but okay on flat ground. At 55 mph, the engine was rolling along happily at 1,200 rpm, which gave me a 200-rpm margin before I’d have to think about downshifting.

I can’t say how an automated transmission would have handled it, but my inclination is to run the engine down as low as possible before downshifting without trapping myself at too low an engine speed. I suspect an Eaton automated would have opted for higher shift points, and so might have spent more time in 9th gear on the two-lane sections than I did.

 

I did cruise along in 9th for a while on a hilly section of S.R. 394 and was quite pleased with the very spry performance of the engine between 1,500 and 1,700 rpm. Ninth gear gave me a speed range from 45-65 mph at a usable engine speed, so I could have happily left it in that gear the whole time I was in the hills.

The engine responds very nicely to low-rpm operation in the bottom five gears, when I usually shift between 800 and 1,000 rpm. Startability is great with that gear combination. In the higher gears, shifts were comfortably made at 1,200-1,400 rpm.

The engine brake was fantastic for such a small-displacement engine, and when the revs get up to 2,100 or so, you can really feel it digging in. With today’s low-rpm operation, it’s easy to forget about the top 500 rpm in the engine range, but that’s where the engine brake works best.

On a less technical level, I found the engine to be very quiet, and it has a very pleasant low growling sound. It won’t bother anybody. Because the engine is so light, I’m sure it will be a hit in weight-sensitive applications. The variety of ratings is astounding; they go up in roughly 25-rpm increments from 325 to 500. The 500-rpm rating is vocational only; on-highway goes as high as 475. Torque ratings run from 1,350 to 1,700, and there are several multi-torque ratings in there as well, 1,550/1,700 and 1,450/1,650.

I think the X12 is exactly the right engine for the emerging regional haul market, and Cummins has nailed the performance curves. There’s nothing missing on this engine except a few hundred surplus pounds of engine block.

Write a Comment

Your email address will not be published. Required fields are marked *