Bottom Line
High Performance Diesels
Drive by the gauges

Did you miss the Louisville Truck Show? If you did, you missed the best truck show of all time. The weather was perfect for Pride and Polish, and the trucks were absolutely beautiful.

We had our chromed NTC 700+ horsepower Cummins engine on display. The number one question asked was: "How much torque will it produce and will the transmission hold up?" This engine will produce in excess of 2200 pounds feet of torque. As for the transmission, we recommend a 14-6-13 or the newer 18 speed. Many of these engines are coupled to a 12-5-13 speed and they are holding up just fine. We do not experience driveline failures with our high performance engines. It is our opinion that driveline failures are a result of using too much power when starting out and accelerating through the gears. It's not how fast you go from 0 to 70 mph that matters, it's how well you maintain your desired cruising speed. If the power is used to maintain speed, the driveline will not suffer from the additional torque.

When building high performance engines, we always install a liquid-filled fuel pressure gauge, turbo boost gauge, and a pyrometer. When accelerating from a dead stop, you never need to use more than 75 lbs. of fuel pressure in the low side of the transmission. A stock NTC 350 develops 155 lbs. of fuel pressure and 18 lbs. of turbo boost, and a 400 produces 176 lbs. of fuel pressure and 25 lbs. of turbo boost.

With these figures in your mind, all you have to do is drive by the gauges and stay under 25 lbs. of turbo boost when accelerating through the gears. Why 25 lbs. or less? A 14-6-13-speed transmission is rated for 1400 lbs. ft. of torque and that is what a stock NTC 400 Cummins Engine produces. If you divide 1400 by 25 you get 56, which means that for every pound of turbo boost the NTC 855 cu. in. engine develops 56 lbs. ft. of torque. You (the owner and driver) decide how much power is necessary to move the load.

Now get out your calculator and make a list. Tape it to your instrumental panel until you have it memorized: 15 lbs. boost=840 lbs. ft. torque, 20 lbs. boost=1120 lbs. ft. torque, 25 lbs. boost=1400 lbs. ft. torque, 30 lbs. boost=1680 lbs. ft. boost, 35 lbs. boost=1960 lbs. ft. torque, 40 lbs. boost=2240 lbs. ft. boost, 45 lbs. boost=2520 lbs. ft. torque, 50 lbs. boost=2800 lbs. ft. torque. Some of our high horsepower Cummins engines will produce 52 lbs. of turbo boost.

If you are one of the chosen few owner-operators that own a KTA 1150 cu. in. Cummins engine, your multiplier is 66 lbs. ft. of torque per one pound of turbo boost. Butch Shuman of Tye, TX, has one of our Twin-Turbo HVT-KTTA 1150 cu. in. engines that produces in excess of 54 lbs. of turbo boost, which equates to 3564 lbs. ft. of torque and Mr. Shuman does not destroy transmissions. If you are passing through Tye, stop by Shuman Equipment Co. Butch would love to show you his 1978 extended hood Kenworth. This truck will spin the driver tires while pulling an empty bull rack at 85 mph and using 54 lbs. of turbo boost. Tire and driveline life are all controlled by the drivers right foot.

The next question from the Louisville Show was fuel mileage. What kind of fuel mileage does a 700 hp engine get? Cummins and Caterpillar did a study on how much horsepower it takes to pull a loaded van grossing 80,000 lb. across a level interstate at 70 mph with no head or side winds. The two companies were within 6 hp of each other, while 273 hp is required. Now, if your engine only produces 300 hp at 2100 rpm, where do you think your foot is to maintain 70 mph? Flat on the floor, and forget 70 mph when you come to a slight grade. You're dropping a gear and putting your foot flat on the floor again. What a terrible way to drive.

Back to the boost gauge. Each pound of boost equates to about 16 hp. Seventeen pounds of boost will produce 272 hp, and that is what you need to maintain 70 mph on the level with no head or side wind, while pulling a van. A flatbed or drop deck trailer loaded with plate steel should require less power because of wind resistance. And I'm sure that I don't need to tell you a bull rack pulls harder than a van. Drive by the boost gauge; the more boost you use, the more horsepower you're using. Speed takes power and power is fuel consumed.

Because of the 1/2 in. longer stroke of the 3406 Caterpillar engine, each pound of boost equates to about 19.3 hp. Stroke produces torque. That's why a V8 diesel engine is low on torque. It has a short stroke.

CPL stands for Control Parts List. Please know your CPL when you call our shop and want to discuss horsepower or order parts. The CPL will inform us as to which engine you have. With this number we will know which injector, turbo, camshaft, engine timing and piston you use, as well as what year your engine was manufactured. If you don't have the CPL number when you call we will ask you to get this number off the engine tag. If the tag is gone then you will have to get the engine serial number off the block, which is below the rear head on the driver's side of the engine. You should keep both of these numbers in your wallet at all times.

If you missed Louisville, we'll see you in Las Vegas for the International Trucking Show at the end of June.

If you would like our booklet on high performance Cummins diesels, give Aimee a call at 724-274-4080. The booklet is also available at Our e-mail addresses are, and

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