Determining the correct pushrod length for your big block Chevy is crucial for optimal engine performance and longevity. A pushrod that's too long or too short can lead to a range of problems, from poor valve adjustment and reduced power to catastrophic engine damage. This guide will help you understand the factors influencing pushrod length and how to accurately measure and select the right ones for your build.
Understanding Pushrod Function
Before diving into specifics, let's briefly review the pushrod's role. In a pushrod engine like the big block Chevy, the pushrod acts as a mechanical link between the rocker arm and the camshaft. It transmits the cam's motion to open and close the valves. The precise length ensures the rocker arm operates correctly, providing the appropriate valve lift and timing. An incorrectly sized pushrod compromises this delicate balance.
Factors Affecting Pushrod Length
Several factors influence the ideal pushrod length for your big block Chevy:
- Cam Lift: Higher cam lift necessitates longer pushrods to accommodate the increased valve travel.
- Head Gasket Thickness: Thicker head gaskets increase the distance between the cam and rocker arms, requiring longer pushrods.
- Block Deck Height: Variations in block deck height directly impact the pushrod's overall length requirement.
- Rocker Arm Ratio: The rocker arm ratio (the relationship between rocker arm movement and valve lift) affects the pushrod's effective length.
- Pushrod Material and Manufacturing Tolerance: Slight variations exist between pushrods, even within the same specifications.
Methods for Determining Pushrod Length
There are several ways to determine the correct pushrod length for your specific big block Chevy engine build:
1. The Measurement Method:
This method requires careful measurement and calculation. You'll need:
- Precision measuring tools: A high-quality measuring device is essential for accuracy.
- Accurate knowledge of your engine's components: This includes cam lift, head gasket thickness, block deck height, and rocker arm ratio.
- Formula: The formula for calculating pushrod length is complex and requires a thorough understanding of engine geometry. Improper calculation can lead to incorrect results.
This is not recommended for DIYers without prior engine building experience. An incorrect measurement can result in engine damage.
2. The "Pushrod Length Check" Method:
This is a more practical approach, often preferred by experienced engine builders. It involves installing the engine components, setting the valve lash, and then using a pushrod length checker to find the optimal length.
This method requires:
- Assembled engine: The engine must be assembled with the camshaft, lifters, rocker arms, and valve train installed.
- A pushrod length checking tool: This specialized tool helps determine the optimal pushrod length.
- Mechanical knowledge of valve adjustment: It's imperative to correctly set valve lash before measuring.
This method provides the most accurate results but requires skill and specialized tools.
3. Consulting a Professional Engine Builder:
For many enthusiasts, the best approach is to consult with a reputable engine builder. They possess the expertise, tools, and experience to accurately determine the correct pushrod length for your specific engine build, ensuring optimal performance and longevity.
Consequences of Incorrect Pushrod Length
Using pushrods of the wrong length can lead to several undesirable outcomes:
- Reduced Engine Power: Improper valve timing and lift negatively impact engine performance.
- Premature Wear and Tear: Incorrect pushrod length can cause excessive wear on lifters, rocker arms, and valves.
- Valve Damage: Extreme cases can result in bent pushrods or damaged valves, leading to costly repairs.
- Engine Failure: In severe scenarios, incorrect pushrod length can result in complete engine failure.
Conclusion
Selecting the correct pushrod length for your big block Chevy is crucial. While the measurement method exists, the "pushrod length check" method or consulting a professional engine builder provides a safer and more accurate route to optimal engine performance. Remember, the cost of a professionally determined pushrod length is far less than the cost of repairing or replacing damaged engine components due to an incorrect length.
