Air/fuel control key to engine performance: Continental Controls' products combine to increase output, fuel efficiency while holding the line on exhaust emissions

Diesel Progress North American Edition,  May, 2005  by Mike Mercer

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In visiting the Coalinga facility, CCC personnel confirmed that the engines could not carry more than about 60% of their rated load because of detonation. The evaluation showed that each engine's original intake manifolds had been modified to add a second carburetor--most likely to improve performance. The modification split the single intake manifold into two--one manifold and carburetor fed the first four cylinders while the second fed the other four cylinders.

"When the air-fuel flow through the intake manifolds was analyzed from the firing order data, the problem became obvious," said CCC's Ross Fisher. "Without a split in the manifold, there would always be two cylinders drawing in an air-fuel mixture. However, when the manifold was split, the second manifold has no cylinders drawing fuel in the 90[degrees] to 180[degrees] crank angle range, the result is that the fuel-air pressure in one manifold increases to near atmospheric as the other manifold fills, permitting a larger charge of fuel to be admitted into cylinder number seven when its intake valve opens. The same thing happens later in the other manifold where cylinder number two gets an excessive airfuel charge. This causes these cylinders to detonate first, preventing further loading of the other cylinders."

To compound the problem, it was determined that the diameter of the intake manifold was less than the piston diameter and thus, the manifold had no storage capacity for the air-fuel mixture. In addition, the pressure in the manifold varies with flow since the throttle plate position does not vary on a cylinder-to-cylinder basis.

CCC's solution included installation of a larger diameter intake manifold, along with the ECV5 emissions control valve and twin VM-350 mixing venturi were to be installed.

Each venturi measures the volumetric airflow and provides the throat pressure of the venturi at an external port. The throat pressures of the venturi are compared to balance the volumetric air flow when adjusting the throttle plates. A second measuring port on the venturi is the pressure of the fuel in annulus around the venturi. The pressures in the ports of the venturi are compared and balanced by adjusting the butterfly valves in the gas inlet port of the venturi.

Other modifications to the engines were the replacement of the oil bath intake air filters with dry panel-type filter elements from Spitzer, Altronic CPU 2000 ignition systems and Hilliard vacuum demisters for crankcase vapors. Additional improvements to the engines recently included cartridge-style spin-on oil filters and the addition of Inconel metal exhaust valves. The valve material change allows the engines to run harder at higher temperatures. According to Blumert, the last step to improve engine efficiencies involved the use of synthetic lubricants.

"We basically wanted to get rid of the carburetors to remove restriction from the intake system to get more air through the engines and get more horsepower out of them," said Blumert. "In the process, we eliminated the detonation problem and improved the fuel efficiency. The cost to upgrade these engines was less than the cost to replace them. These engines still run seven days per week, 365 days per year.