🔧Mid Lift Theory Explained | Perfect Rocker Arm Geometry, 351 Cleveland #dragracing #racing

Welcome back to DragBoss Garage! 🔧🔥 In this video we break down the basics of rocker arm geometry and the Mid Lift Theory, and how these concepts affect valve train accuracy, camshaft performance, and overall horsepower. ⚙️💥 A huge shout out goes to Russell Saliba from Australia 🇦🇺, who has extensive experience building high horsepower Cleveland engines. Russell showed me a very interesting technique using laser alignment 🔬 to check the relationship between the rocker arm tip and the valve stem tip. 📐 The theory: At mid lift of the camshaft, using the actual valve train with real springs (not checking springs), there should be a 90° relationship between the valve stem tip and the rocker arm tip. Why does this matter? 🤔 When you assemble the engine with the actual valve springs and full valve train, several factors begin to affect cam motion, including: • Pushrod deflection • Valve spring pressure • Valve train flex and movement These conditions mimic what happens in a running engine. 🏎️💨 If the rocker arm contact angle is not close to 90° at mid lift, you are actually losing some of your camshaft’s designed performance. That loss affects: ⚡ Valve Lift ⏱️ Duration 🚀 Valve Velocity Most engine builders evaluate rocker arm geometry using the contact patch method with machinist dye. The common belief is that the thinner the contact patch, the better the geometry. However, rocker geometry changes anytime you modify engine components, including: 🔧 Camshaft changes 🔧 Valve train component swaps 🔧 Decking the block 🔧 Milling cylinder heads 🔧 Different rocker arm systems When rocker geometry is incorrect, the results can include: ❌ Loss of camshaft performance ❌ Increased friction ❌ Excessive side loading of the valve in the guide ❌ Accelerated wear on valve train components In this video I demonstrate both the Mid Lift Theory and the contact patch method so you can compare the two approaches. 🧠⚙️ For Cleveland engines and similar rocker systems/ stud mount, the contact patch location is adjusted by changing pushrod length. With shaft rocker systems, such as Yella Terra Platinum Series rockers, geometry adjustments are made by adding shims under the rocker stands. You can fine tune so to speak with different length push rods. 📍 Longer pushrods or shims under pedestals move the contact patch toward the exhaust side 📍 Shorter pushrods or removing shims move the contact patch toward the intake side This video is meant to explain the general theory and demonstrate one practical method for checking rocker arm geometry. There are many deeper technical discussions on Mid Lift Theory, but this gives you a solid foundation. 🔬⚙️ 🙏 Special thanks to Russell Saliba for sharing his knowledge and experience. 🏁 Special thanks as well to Dr. Ron Racing — Real Pro Stock Cars! 🔥 Stay tuned… a lot more engine tech and racing content coming soon from DragBoss Garage. #dragracing #enginebuilding #valvetrain #rockerarmgeometry #midlifttheory #horsepower Always seeing and learning something new at DragBoss Garage" https://www.amazon.com/shop/dragbossg... My Ford 351 Cleveland Website https://www.tapatalk.com/groups/351c/ Join this channel to get access to perks: DBGU/ Darin Morgan Induction You got to see to believe.    / @dragboss351cleveland   Donate to DBGU/DMI, to help us, help you, get the most for your program, Racing, Personal, or business. https://www.paypal.com/donate/?hosted...