Understanding the Importance of Valvetrain Adjustment in Your Car

Valvetrain adjustments are critical for maintaining optimal performance in certain types of vehicles, particularly older high-mileage cars and high-performance vehicles. This article aims to explain why such adjustments are necessary and how they can affect the performance of your car.

High Performance Vehicles and Valvetrain Adjustments

Valve lash adjustments are especially important in high-performance vehicles, especially those that run on nitromethane. A single 0.003” difference in lash can translate to a top speed difference of 3-5 mph in Funny Car or Top Fuel classes. These classes feature powerful engines, primarily all-aluminum engines, which heat up quickly and cause valve lash to change rapidly.

My practice when servicing a nitromethane-burning Hemi was to set the valves to 0.018” lash when the engine was cold. This setting was increased to 0.020” if the engine was between rounds and still warm. After warming up, the lash would almost always be at 0.028”. It's interesting to note that the engine would "grow" by 0.010” just by warming up!

For performance tuning, we would make adjustments based on varying track conditions. Poor track conditions might require a larger lash to "take cam out of it" by making the cam profile slightly smaller. Conversely, high-elevation tracks like Denver or really tight tracks like Pomona would benefit from tigher lash settings to maximize the cam's performance. Such fine tuning can result in significant speed improvements. For example, a mere 0.005” lash change resulted in a 5 mph speed increase during tests at Las Vegas with the same ET but a higher 1/8 mile and 1000 foot mph readings.

Street-Going Vehicles and Valvetrain Adjustments

While the performance adjustments for high-speed engines are critical, regular valve lash adjustments are equally important for street-going vehicles and high-mileage engines. Over time, components in your car's engine wear, affecting the overall performance and fuel economy. Valvetrain adjustments are necessary to ensure optimal performance and longevity.

Hydraulic lifters, while self-adjusting, are less accurate and may not provide the precise adjustment needed for maintaining good fuel economy and low valve train noise. In contrast, most diesel engines use mechanical lifters, which are more accurate but require periodic adjustments to ensure that the valves are opening and closing correctly as the engine ages.

Conclusion

Valvetrain adjustments are essential for both high-performance and street cars to maintain optimal engine performance. Whether you're tuning a race car or an older, high-mileage vehicle, understanding the importance of valve lash adjustments can help you achieve better performance and reliability. Regular adjustments can help prevent issues and ensure that your car runs smoothly and efficiently.