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Accelerative forces induce cylinder imbalance in carbureted or throttle-body injected engines by steering the fuel in the direction of the force. This cylinder imbalance manifests itself as decreased performance, decreased fuel economy, and decreased reliability. Accelerative forces do not induce cylinder imbalance in port-injected engines because fuel distribution is not readily impacted. Race engines are subjected to a variety of extreme accelerative forces, including fore-aft forces during acceleration and braking, and lateral forces during cornering. It is not unusual to see forces much greater than the force of gravity. Both airborne fuel droplets and fuel deposited on the manifold walls and floor are steered by these accelerative forces, impacting engine performance and reliability adversely. In this paper, the impact of accelerative forces on combustion performance in a Winston Cup engine are examined.

Development of race engines has traditionally been a very hardware-intensive process. This is particularly true when trying to maximize the performance of a given engine. The engine developer must identify the inadequately designed components, and then attempt to optimally redesign them. Cylinder-pressure based combustion diagnostics can help identify the performance-limiting componentry, and can provide direction for the redesign of that componentry. However, effective analysis requires that exacting care be taken when instrumenting the engine, acquiring the data, and interpreting the results.

Performance of multicylinder engines is dictated by the sum of the contributions from the individual cylinders, each of which must be optimized to maximize the total output. Cylinder-to-cylinder imbalance causes each cylinder to operate differently, making individual-cylinder optimization a challenge. Unfortunately, cylinder-to-cylinder imbalance exists in all multicylinder engines, even those in which careful steps are taken in design and manufacturing to prevent it. While optimizing each cylinder of a multicylinder engine in high-volume production applications is not feasible, it is feasible in racing applications and can provide a significant competitive advantage. This paper investigates causes of cylinder-to-cylinder imbalance and discusses techniques to optimize race engine performance one cylinder at a time through the systematic optimization of individual-cylinder intake valve closing, spark timing, and compression ratio.

Engine cylinder-pressure data is generally acquired using piezoelectric pressure transducers because of the many advantages they offer. Unfortunately, a serious and difficult-to-detect disadvantage is variability introduced into the raw data by thermal shock occurring at the transducer face. Transducer manufacturers are aware of this problem and have produced special designs intended to minimize thermally-induced output drift. Although improvements have resulted, the problem continues to exist. However, thermal shock can be reduced by properly mounting the transducer. This study reviews the theoretical principles dictating performance of remote-mounted transducers and examines the influence of the mounting scheme on pressure-data quality. The three feasible mounting schemes studied were flush mount, remote mount via a single passage, and remote mount via multiple slots.

Two disadvantages of using piezoelectic pressure transducers to measure cylinder pressure are the sensitivity of the transducer to temperature and the necessity to reference the output to absolute pressure (pegging). Transducer drift driven by the combustion event, often referred to as thermal shock, enhances measured cyclic variability by exaggerating the effects of actual cyclic variations in combustion temperature. Any artificial variability that persists until the portion of the cycle used for pegging offsets all of the referenced measurements of that cycle by the magnitude of the variability. This study reviews several methods of pegging, and examines the extent to which the four most viable methods propagate thermally-induced intracycle and intercycle measurement variability. It is preferable to peg when artificial variability is minimized, which occurs when the transducer output is least affected by the thermally transient nature of the engine cycle.