6. Horsepower and Torque: Proper STC Valve Adjustment

Words and thoughts from the man who started it all.

6. Horsepower and Torque: Proper STC Valve Adjustment

Postby Fernando on June 1st, 2009, 1:38 pm

This is the 50th article that we have written pertaining to Cummins diesel engines and how to produce as much as 100% more power using genuine Cummins engine parts. All of this power would not have been possible if it weren’t for the help and dedication of one particular Cummins engineer, Mark Chapple of Columbus, Indiana. Mark has been my guiding light and closest friend in the relentless pursuit of producing horsepower from the Cummins engine.

Mr. Chapple started with Cummins right out of high school at the age of eighteen. His first job was on the assembly line putting engines together. While working daylight he enrolled in night school at a college in Indianapolis studying mechanical engineering. Prior to graduating from college the management at Cummins saw the potential of this young man and promoted him to the engineering department.

I had the privilege of meeting Mr. Chapple on the phone around 1984 after placing a phone call to Columbus, Indiana asking for the engineer responsible for developing the small cam Magnum 400 Recon engine, CPL 695. I was transferred eight times before getting Mark on the phone. My question was how can this engine start, let alone run with a timing of .056 and a compression ratio of 14.0 to 1. Mr. Chapple spent the next two hours explaining to me the effects of compression ratio, timing, injector flow, injector cup size, fuel pressure and volume and what happens if you don’t follow certain guidelines when increasing horsepower in a diesel engine. When that phone call ended I knew that I had a new friend and my life and the life of every owner-operator in this country that drove Cummins engines was about to change. One of the projects that Mark Chapple and I worked together on was to develop 700 horsepower from a BCIII engine using STC injectors, twin aftercoolers and twin turbos. This engine produced 700 horsepower on the dyno at Cummins in Monroeville, PA. and was installed in Jerry Hairhogger’s Kenworth from Wampum, PA.

In January 1996 while I was visiting with Mark in his office he opened a letter which changed his life. At the young age of 51 he had enough seniority to retire. This man truly loved his work at Cummins Engine Company and did not want to retire. However, the retirement package was too good to refuse. Mark Chapple, Cummins engineer extrordinaire, is now at home in his own shop developing high performance engine parts for Dodge Cummins trucks. Mark’s 1995 Dodge produces over 300 horsepower and runs 0 to 60 mph. in eight seconds.

For those of you who have been following our articles for the past 50 months now you know where a lot of the technical information that has been made available to you has come from. As Paul Harvey would say, now you know the rest of the story.

With great pleasure I dedicate this 50th article to you Mr. Mark Chapple for all of your help, understanding, knowledge and friendship during the past twelve years. Thank you.

On to horsepower: We have preached about retarding engine timing when the horsepower is increased to reduce internal pressure. This pertains to all Big Cam I, II, III, and early BC IV engines with locked in timing. If your engine has MVT (mechanical valve timing) or STC (step timing control) you already have retarded timing. That’s why the NTC 444 runs so well with high flow injectors and high volume fuel pumps and don’t forget the dual fuel line kit.

Setting valve and injectors: Years ago with small cam engines we would set the pointer on the accessory drive on A or 1-6 v.s. and set the injector and valves on no. 1 cylinder if both valves were closed. This is now called the outer base circle method. Then came the dial indicator method where we would set no. 3 injector and no. 5 valves when the accessory drive was set on A or 1-6 v.s. In 1978 top stop injectors came along. They were to be set at finger tight, zero lash or 5 to 6 inch lbs. on no. 3 injector and .011 intake valve and .023 exhaust valve on no. 5 cylinder on the "a" mark of the accessory drive. This is called the inner base circle method.

Now, in 1988 came the STC injector and we are back to setting them on the outer base circle method. Just like the old NH 250 and NTC 335’s. You will need a Snap-On dial type 0 to 150 inch-pound torque wrench. Bring up "A" on the accessory drive and if both valves are closed on #1 cylinder adjust the injector and valves on that cylinder. Then proceed to the "B" mark and adjust the injector and valves on #5 cylinder. With the outer base circle method the intake valve is set at .014 and the exhaust valve is set at .027. Now here’s the kicker, the CPL of your engine determines the amount of inch lbs. the injector is set to. For instance, if the CPL is 821, 833, 903, 904 or 1215 the setting is 105 in.-lbs. On CPL’s of 827, 910, 1185, 1188, 1210, 1211, 1256 and 1280 the setting is 90 in-lbs. The N-14 with CPL’s of 1374, 1380, 1395, 1405, 1507, 1530, 1532, 1607 and 1652 require 125 in-lbs. and the valves are all .014 intake and .027 exhaust.

If you purchase your custom flowed injectors from Diesel Injection of Pittsburgh we will furnish to you the correct settings. By keeping the valves and injectors adjusted the life of the engine will increase by about 20% and perform much better. You can purchase the Snap-On torque wrench and other necessary equipment at our shop to make it possible for you to adjust your own valves and injectors.

Crazy Norm Murakami, the high powered owner operator from Costa Mesa, Ca. wants to enter his Western Star with the 900 + H.P Cummins in the Pony Express race. This high-speed race starts at Battle Mountain Nevada and goes to Austin, NV. a distance of 84 miles wide open. Norm wants to have a G.V.W. of 60,000 and maintain 125 to 130 mph. for the distance.

Quote of the month: There are doers, and there are those who are afraid. Which are you?
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