Bottom Line
High performance diesels
Question of the month is from Sam Pierson of Provo, UT: I am in the process of rebuilding a KT 450 to be used in a new Kenworth glider kit. The truck will be used for heavy hauling and I would like to have around 800 hp. What pistons can you furnish to me and where should I set the timing?

There are three pistons available for the K series Cummins Engine. The 450 hp engine has a rather weak piston that usually cracks up the skirt, across the dome and down the other skirt (90 degrees from the wrist pin). Many times we have pulled pistons out of KT 450s only to find the rings and wrist pin holding the piston together. Do not use this piston when rebuilding a K series engine; the compression ratio is too high (15.1 to 1). The KTA 525 and 600 both use a piston with a compression of 14.5 to 1, which works very well when the timing is set at .126 to .128. The stock timing on the K525 and the K600 is .118. When building horsepower, however, the timing must be retarded to keep from cracking or melting a piston.

The strongest K series piston to use is the KTTA 700 hp, which has a compression ratio of 13.7 to 1. This piston develops tremendous power when timed at .126 to .128 and used in conjunction with our high-flow injectors and high-volume fuel pump.

With one Holset Turbocharger, 800 hp is possible. But there is a killer twin turbo system available for this engine and it looks awesome when coated with Jet Hot ceramic coatings.

You will have to fabricate your own dual fuel line system for the K engine. Here are some pointers on how to build the kit:

As with any diesel engine, liner protrusion is critical. Do not settle for anything less than .007 liner protrusion. To hold the power, we use a head gasket that has been cut to accept a fire ring. This is an old engine building trick used by drag racers. It works well with the K series engine.

Cummins Recon has many heads available for this engine. You should contact Gary at our shop to discuss the various heads.

Sam made a wise choice of engines for heavy hauling. The K series engine has the strongest bottom end of any diesel engine ever built for on-highway use. Make sure that your new KW glider kit will be set up for an air-to-air charge cooler. We will supply you with a Charge Air Concepts cooler that will hold the turbo boost. It will never crack because it is not welded together.

Bill Toste of Girard, OH, asks another good question: Is there a new method of torquing the connecting rods of my N14-500 hp engine?

The connecting rod for the 1994 and newer engines with articulated pistons has increased loading of the rod-bearing area. The articulated piston is the two-piece steel top aluminum skirt piston used in N-14 460 hp and higher engines. This piston is stronger than all aluminum pistons and can handle more internal combustion pressure.

The new torque specification is 95 ft.-lbs. plus 60 degrees (give or take five degrees). This sounds really confusing, so to make the job easier Cummins has a service tool called a torque angle socket gauge (part number 3824520). This socket is marked with a zero (start) point, a specification window, and an out of limits (OOL) line.

Here are the instructions for using the torque angle socket gauge: Torque booth connecting rod capscrews to 95 ft.-lbs. With the socket on the capscrew, draw a line from zero (start) point across each capscrew head to a point on the rod cap. This line is the gauge line for the angle portion of the specification (60 degrees). With the zero point on the socket gauge aligned with the mark on the capscrew head, torque both capscrews to 205 ft.-lbs. With the socket gauge in position, check to see if the fixed mark (on rod cap) is within the window of the gauge. If the fixed line is past the OOL line, replace the capscrew and repeat the torquing procedure. You'll need to replace the capscrew if it goes past the OOL line because the bolt is stretched and will not hold the 205 ft.-lbs. of torque. If you don't replace the bolt or capscrew, the rod bearing may spin.

Stop by your local Cummins Distributor and ask for Service Parts Topic No. 94T1-5. There are illustrations in this service parts topic that will help you understand how to properly torque the rod bearings. Good Luck!

The time has come for us to finally have a high performance computer for the N14 Select engines. The first will be tested this month at our shop in Pittsburgh. Significant gains in horsepower and torque will be available at the flip of a switch. This computer will not replace the stock engine computer. It will be a separate and interchangeable piece of equipment working in conjunction with the existing engine computer. The first series will only work on the select engines, and NOT the select-plus engines. By the end of 2000, the select plus performance computer will be ready. Once we perfect the computer for the Cummins engine we will start on the Caterpillar computer and then onto the Detroit Diesel computer.

We have started a list of owner-operators who are anxious to have more power from their N14 Select engines. If you would like to be on the list please send your name, address, and phone number to our shop. Please do not call and ask particulars about the performance computer, because we will not have any more information until the first computer is tested. You will read about the progress of this unique electronic apparatus in the next issue of Land Line.

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.