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High Performance Diesels
Using performance products on the L-10

Land Line reader Doug Forraht, from Berrien Springs, MI, sent us e-mail asking if any of our performance products for the NTC engines would work on the L-10. His truck is an IH2375 L-10-270 HP.

Our answer is yes. The fuel system on the L-10 engine is the same as the NTC engine. Since Doug's engine does not need to be rebuilt we are going to outline external changes that will result in an increase of horsepower and torque.

Not knowing the age of Doug's truck, our first recommendation is to replace the fuel suction line and increase the size by two numbers. The stock size is #10. A #12 will allow more fuel to pass with less restriction.

Next, send the fuel pump and injectors to our shop to be re-calibrated. It takes fuel to make power. Without a matched set of high-flow injectors and a high-volume fuel pump, there will be no power.

Install a liquid-filled fuel pressure gauge, turbo boost gauge, exhaust manifold pressure gauge, and pyrometer so you will be able to monitor the performance of the engine while driving.

Remove restrictions from the exhaust system and especially the baffles inside the muffler. Dual exhaust always helps to relieve backpressure.

Air cleaner

We will determine the CFM (cubic feet of air per minute) requirements of the engine and you will have to call Donaldson with the part number of the air cleaner housing to obtain your current CFM rating.


With the turbo boost gauge and exhaust back pressure gauge installed, we can now determine if the turbocharger is large enough to supply air to the engine. The truck should be loaded and driven up a hill at wide-open throttle and the gauge readings recorded.

The Fuel preporator

By removing the air from the fuel and pressurizing the gear pump of the PT fuel system, the net result in horsepower of the L-10 should be approximately 30 HP.

Always use Lucas fuel conditioner with every tank of fuel. Diesel fuel is very dry today and does a poor job of lubricating the fuel system. The Lucas fuel conditioner does an excellent job of lubricating the barrels and plungers in the fuel system. Many owner-operators have reported back to us that an increase of two to three pounds of turbo boost is noticed after using the Lucas. Also, the Lucas oil stabilizer helps to protect the rod and main bearings in a performance engine. Added power increases the load on the bearings and it's nice to have that extra lubrication in the oil.

Doug, remember this: Trucks are like racecars. They work their heart out on every hill. All of the changes we have listed do not have to be made at once. Do one change per month and with each change you will notice an increase in performance. With each change there will be a cumulative effect. However, each change will be small. The final result will be a huge increase in performance and the truck will be fun to drive. The fuel pump and injectors will result in the largest increase in power.

When it's time to rebuild the engine, we have a genuine Cummins performance piston available. The advantages of this piston over the stock piston are as follows:

  • Dual Ni ring lands. The two top rings have the steel insert.

  • The wrist pin bore has been contoured to more evenly distribute the stress loading on the piston.

  • The wrist pin is 4mm longer.

  • The top of the piston has been anodized to relieve stress.

During the rebuilding process, a different cam key will be supplied to retard the timing. The retarding of the timing allows the piston to be closer to top dead center before the injector fires. The retarding of timing reduces the combustion pressure on the piston.


If your camshaft needs to be replaced, the new design camshaft is microfinished and must be used with microfinished cam follower rollers to achieve durability improvements.

Head bolts

If your engine currently has flange style cap screws, they must be replaced with the new design head bolts and washers. The new bolts are torque-to-yield style cap screws. If your engine is equipped with this style cap screw you must use gauge part #3823546 to check for proper length. Head bolts do stretch.

Water temperature

With the addition of horsepower, the water temperature may rise an additional 12 degrees. During the rebuild process, it is advisable to replace the water pump and have a radiator shop clean and flush the radiator.

The block

It is recommended that your engine block be 1988 or newer. Starting with serial number 34569763, the structural integrity of the block is greater.

Strictly my opinion: The L-10 is a great medium-duty engine and should be used as such. To me, medium duty is 60,000 GVW or less. Remember the old saying from back in the '60s, "You can't beat cubic inches." If you're around 80,000 lbs., build an NTC 14-liter engine. Heavy haulers: The 1150 cu. inch "K" series is still the ultimate engine. Don't ask a boy to do a man's job. 

My booklet is now available for viewing or download on the World Wide Web. The address is Our e-mail addresses are and

If you would like our booklet on high performance Cummins diesels, give Aimee a call at 724-274-4080. There is a $9.00 charge for shipping and handling. Just call us with your Master Card, Visa, American Express or Discover card number and we will get one out to you. Or, you can send a check or money order to Diesel Injection of Pittsburgh, PA, 1403 Freeport Rd., Cheswick, PA, 15024.

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.