C-12 Engine Questions

[Dick Simonis]

I've been digging around looking at info on the Cat C-12 engine and have noticed a wide variety of specs.  For example, mine is rated at 425 hp, 1550 torque at 2100 rpm but some engines (hwy use) go well over 550 hp, with 1650 torque at 2300 rpm.  Marine engines go even higher with one rated at 750 Hp.  These numbers come from Cat so they are not "tuneed" by a performance shop.  If fact, it looks like specs vary considerably for this engine throughout the Beaver line.

Granted the higher numbers are for newer engines than mine and seem to be "ACERT".  Don't know if that means anything.

I'm just curious what Cat does that makes such significant power differances.  One source commented that you could go into a Cat dealer and ask for a "marine" tune that really ups the power output.

I have no intention of changing anything, this is just a curiosity question.  Also, and I know this has been beat around, the 2300 rpm seems a common max engine speed for non-Jake equipped engines.

[Marty and Suzie Schenck]

Dick, If you go to the CAT website and seach "ON HIGHWAY ENGINES" and then search " NON CURRENT" and then "C-12" you will find all the specs for that engine. It was only manufactured from 1995 to 2003 and from 335 to 505hp for ON HIGHWAY use. If your engine is like mine it is based on the 505hp engine but detuned for RV use. Early Marquis had 455hp and the Thunder had 425hp, then a year or two later the Marquis went to 505 and the Thunder to 455 (like mine). Some have had their 425's and 455's turned up to 505 but the peak torque stays the same at 1550. I talked to several CAT reps (I use to work at the PACCAR Tech Center) and they all say that turning up the horse power will on let you go from stop light to stop light quicker and will not help you climb a hill faster. You may also lose mileage. Mine runs fine and I'm OK with the mileage (8-8.5), so I'm leaving mine alone.
Marty

[Dick Simonis]

Don't get me wrong, I'm not even considering changing my engine output....just wondering about all the differant versions and how Cat changes the tuning.  Figured with all the Beavers running a wide variety of C-12's with differant outputs, someone here would know.  Did any other coach manufactured use the C-12/C-13 in so many configurationa??

I'm also still strugging with understanding the max rpm rating of 2100 when so many are rated to 2300. (going back to Jake brake question).

Your answer certainly make sense that Cat would just derate for specific applications.  I've even seen some rated for 390 hp.

Dick

[Gil_Johnson]

Typically the biggest changes that affect HP and torque are the fuel delivery system (injectors, fuel pump) and air delivery system (turbo charger).  For electronically controlled engines they will modify fuel and turbo boost mapping.

Marine engines will always be capable of the most power.  This is because the engine cooling system is better than all others.  Sea water is used instead of ambient air for cooling.

[Jim Gill]

Dick
When Cat decided to redesign most of their engine line in 2001 to meet the impending US EPA emission standards which were being imposed on all new on-highway, and later off-highway, diesel engines, they dumped the old engine model nomenclature (3304, 3306, 3408, 3412, etc.) which defined the engine bore and the cylinder configuration of each engine and instead used a "C" followed by the approximate displacement in liters followed by the "ACERT" acronym for the nomenclature of these new, emission compliant engines. ACERT stands for "Advanced Combustion Emission Reduction Technology".

The number designation in the engine model designation represents the approximate engine displacement in liters. A single liter is equal to 61.02 cubic inches so a C9 (an I6 engine with 537 cubic inches of displacement) is technically closer to 8.8 liters but it's called a C9. A C13 (an I6 engine with 763 cubic inches of displacement) actually displaces only 12.5 liters but it's called a C13.

ACERT technology involves a combination of new engine designs matched with a systems approach to air management, extremely high pressure and technologically advanced fuel distribution systems with computer management of the combustion process and a variety of aftertreatment configurations. Though the ACERT concept is similar across engine models and families, there are also some differences depending on the intended application of each engine arrangement.

Hope this helps a bit.

Jim Gill
  

[JimDyer]

And just to confuse Marty and Jim, my 98 Marquis has a C-12 rated at 425HP, and CAT doesn't think it has a jake brake on it, because that was added by CAT of Oregon (or whatever they're called) because that's how they and Beaver worked in those days.......I'm guessing they stocked for Beaver to reduce the order time()

[Gerald Farris]

Dick,
Comparing over-the-road and marine engines is like comparing apples and oranges. There are different emission standards and much different operating conditions. Marine engines run under a constant load and usually at a constant RPM. Also the water to air intercoolers that are used on marine engines are so much more efficient than the air to air units used on highway engines. This increased efficiency increases the intake air density, giving more oxygen for combustion so more horsepower can be produced.

With the lighter overhead of a marine engine (no Jake Brake), higher RPMs are possible, and since horsepower is a calculation of torque times RPMs, more horsepower is possible.

Your 425 horsepower C 12 is probably rated at 1450 foot pounds of torque, however it can be reprogrammed to either 425 hp at 1550 lb ft or 455 hp at 1550 lb ft. The 505 hp rating requires hard parts (turbo-injectors) as well as reprogramming. So the rerate to 505 hp at 1550 lb ft is not practical, but the 455 hp at 1550 lb ft rerate is arguable worth doing.

Gerald      

[Edward Buker]

The 505HP version did require new iron as Gerald said. It included a piston redesign allowing more oil flow for cooling and more robust rings. Some info from cat...

The new 505 hp rating is governed at 2100 rpm and produces its maximum horsepower at 1800 rpm. Peak torque is 1550 lb.ft. at 1200 rpm with a 31 percent torque rise. Cat said the new rating meets all current on-highway U.S. EPA emissions standards.

 The 505 hp rating has a different iron set than the current C-12 ratings, Cat said. Changes to handle the higher horsepower include more robust piston rings and piston cooling jets with more oil flow to handle the higher temperatures, along with software changes to the ADEM 2000 electronic control module.

Must be the pistons and rings were the weak link here. There was also some redesign of the jake brake mechanicals that took place for better durability that can be retrofitted while doing a valve adjustment. I have this 505hp version in a 40ft Marquis with no tag and have been very happy with the performance. At times it still amazes me power wise and we average an honest 8.6MPG.

Later Ed

[Dick Simonis]

Thanks all, that clarifies a lot of the questions in my mind.  It is interesting to watch the torque output climb to 1556, on the Silverleaf, at such low rpm, and can't even hear the engine laboring.  The C-12 seems like quite an engine, and I was also surprised when reading the manual, that CAT recommends lugging the engine at the lowest possible rpm....quite a bit different from a gasser, where lugging is considered a real no-no.

I suspect that in later Beavers, going to higher HP was somewhat necessitated by weight increases, as more and more options and slides were added.

Who else used the C-12/C-13 in their coaches???

[Joel Weiss]

  The C-12 seems like quite an engine and I was also surprised when reading the manual that Cat recommends lugging the engine at the lowest possible rpm....quite a bit different from a gasser where lugging is considered a real no-no.

We have the same engine as yours and spent much of last summer climbing mountains in WY, ID and MT.  It never broke a sweat.  The greatest temperature rise I saw was ~208 for a moment at 9500 feet on our way to the Tetons.   On normal 6% grades on the interstates, the temp doesn't go above 194.

Although lugging is acceptable with this engine, I don't enjoy having the Allison "hunting" between gears on long upgrades and that behavior is not good for the transmission.  As a result I now control the transmission with the push buttons when climbing, putting it in 4th on the steepest grades.  I'm geared so that I'm turning ~1800 rpm at ~55 in 4th so that's not an issue.  The engine is incredibly responsive in 4th going uphill and the temp rise due to the climb is almost non-existent.  

[Gil_Johnson]

Wow over 500HP and 1500 lb/ft of torque in a 40 footer--I'm jealous.  My 43 footer has the smaller C-9 at 425HP.  There are times, although not many, when the extra power would be nice.

[Edward Buker]

Country Coach used CAT C12s in some of there upper end coaches. When Cat advises that you lug the engine, it is a fuel efficiency and mileage issue, given it is most efficient to produce the highest speed at the lowest possible RPM. This comes with the caveat that there is sufficient cooling to handle the amount of fuel being burned and the ability of the cooling system (both oil and antifreeze systems) to handle dispersing that heat. Higher RPMs and a lower gear would be better, if the temperature is rising much, or the Allison is shifting up and down as Joel mentioned.

Dick, I think that Beaver was buying whatever was available for C12s in each of the years they produced motor homes with some emphasis on higher horsepower as a marketing tool. I do not think the year or weight of the coaches (within reason) made much of a difference. CAT evolves their engines over time and makes available to the marketplace higher output versions that it successfully tests as being durable for the marketplace. The 505HP version was near the end of life for the C12, and based on testing, was released to the firetruck and RV industry, but not to the long haul heavy trucking industry. These applications are more intermittent duty with much lower miles logged in the life of the engine. It is all a trade off....durability vs power output. In our application I'm sure the expected life is in excess of a million miles so we will never wear one of these engines out.

In the end there is not a huge differences between the versions, but it is nice to have a little extra on the hills. The big deal is that you have a C12 and 1550lbs of torque mated with a 6 speed transmission to take advantage of this resource.  I still smile on the hills...

Later Ed

[Phil N Barb Rodriguez]

We have the same engine as you Dick. Don't know what's not to like about it. Ditto on Joel's comment on 4th gear. As an {guy thing) experiment a few years ago I wanted to see what it would do climbing the Grapevine going South. Temp outside was a bit over 100 degs, (in August). I was doing pretty good in 5th gear at the beginning of the climb. A couple miles up the grade a semi pulled over in front of me. My engine temp was ~198. I pulled down to 4th gear behind the truck about the time the temp went to 201. Finally got around the truck about half way up the hill at about 40mph. Picked up speed in fourth, manually shifted to 5th picking up speed. We topped the grade at 65mph and 190degs engine temp and ~400 ft lbs of torque left. Awesome engine! Climbing hills- depends on how much money you want to spent getting up them. Seems like the Grapevine is 12-13 miles.

Several times while going North down the Grapevine I would Jake brake all the way down, 60mph, 2000rpm. Never touched the foot brake one time.

Jeep Cherokee was in tow up and down. I use synthetics in the engines and transmissions on all our vehicles.

Anyone know why "ft. Lbs." was changed to "lbs. ft."?

[Gil_Johnson]

Great question Phil.  Foot pounds still role off the tongue easier than pound feet.  My guess is for accuracy.  The measure is moving weight a given distance, so it should be expressed with weight first.

[Joel Weiss]

As a retired physics teacher, I must insist that the measure has nothing to do with moving a weight a distance.  Torque is a rotational quantity; a pound-foot is the torque exerted by a 1 pound force (the force of gravity on a 1 pound object) at a distance of one foot from the axis of rotation.

So the 1550 pound-feet of torque exerted by a C-12 is equivalent to a 155 pound force being applied at a distance of 10-feet from the rotational axis.  The required force is less the further you are from the axis; the concept of a lever applied to rotational physics.