Bottom Line
High Performance Diesels
MVT and STC Engines

Each day we receive phone calls and letters from owner-operators and mechanics asking various questions. Here's one we hear often.   "I have an older truck in great shape and it's time for a new engine, what should I build, an MVT or STC engine?"

If you have been following our technical articles for the past six years, it is quite evident that we have been very successful producing in excess of 700 horsepower from either engine. So to answer this question we are going to list the advantages and disadvantages of each engine.

To build high horsepower with a Big Cam II, III, or early BCIV is it more feasible and economical to use the high lift camshaft and mechanical variable timing (MVT)? This system was designed for use on the BC II and III so there are no other modifications that must be made other than increasing the travel of the top stop setting on the injector.

Years ago the MVT units had some engineering problems. Reliability was a major concern. Most mechanics in the U.S. are not familiar with how the MVT operates. Instead of learning, they usually denounce the advantage of the system and remove it. The mechanical variable timing system with the automatic oiling system and shutdown toggle switch have been a lifesaver for owner-operators wanting more than 600 hp.

The step-timing control (STC) engine also has benefits if the truck was originally designed for this application. There are only two negative aspects of the STC engine, which are the low-flow cooling system and the price of the injectors. As for power, this engine is a beast, with injectors flowed two sizes larger, a dual fuel line kit and high-volume fuel pump. On the dyno at 300 pounds of fuel pressure, the STC engine will produce 618 hp to the ground, which is 772 flywheel hp.

By now, most of the mechanics throughout this country understand the STC engine more than the MVT engine. Both engines idle with advanced timing to eliminate white smoke. When producing more than 100 hp, the timing is retarded to extend piston life. It is possible to convert the low-flow cooling system to a high-flow system if water temperature is a problem. Here are the items that must be changed (they may vary, depending on CPL):

Water tube to the water pump
Water tube to the oil cooler
Thermostat, seal gaskets and bolts
Water pump and bolts
Water filter head, bracket, and shut-off valves
Idler pulley and bolt

Many times the radiator can have the baffle plates removed and a hose inlet for returning hot water can be installed on the top tank so the existing rad can be utilized. Many times a 425 Cat radiator is used because it's equipped to have an air- to-air charge air cooler mounted in front of it. Charge air coolers do work well with the big cam engines. An old NTC 290 intake manifold is what is used to replace the standard aftercooler when charge air-to-air cooling is being utilized.

Both the NTC/MVT and STC Cummins engines perform superbly above 600 hp. When properly built using ceramic and Teflon coated pistons and premium gold Cummins recon heads, a high performance engine will run a full-service life. Always use genuine Cummins engine parts. The engineering, testing, and quality of genuine parts far exceed the other brands.

On every great running engine there must be a high-volume fuel pump and six-high flow injectors. Regardless of how extravagant you go when building the engine, the fuel pump and injectors along with a few other factors, determine how much horsepower and torque will be developed. If the engine was a human body, the fuel pump would represent the heart, the injectors would be the veins and arteries, and the turbocharger would be the lungs. Naturally they are very important components and help each other function, but the heart (fuel pump) must be strong if you are going to gallop over the mountains like a thoroughbred. LL

Fax, or e-mail Diesel Injection of Pittsburgh, Inc., PO Box 82 Cheswick, PA 15024. Fax (724) 274-8003. Our e-mail addresses are: If you would like a copy of our booklet on high performance diesels, send us a check or money order for $9.00 or give Aimee a call at (724) 274-4080 with your MasterCard, Visa, AMEX or Discover card number and we will get one out to you. Our address is Diesel Injection of Pittsburgh, Inc., 1403 Freeport Road, Cheswick, PA 15024. My booklet is now available for viewing or downloading from the World Wide Web. The address is

The above column is the opinion of the writer and does not necessarily reflect the opinion or beliefs or Land Line Magazine or Cummins Engine Co.

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