For years, it has been standard practice for aircraft engines to see an inverse relationship between engine output and useful life. Our top cylinder girdles turn that notion upside-down. 




By adding structure to a notoriously flexible engine, we have found increased durability and increased performance. From initial FEA simulation up to engine stress testing, over a decade of development on various girdle configurations has gone into this exceptional design. Our girdles are cast from aerospace-grade Magnesium - chosen for it's incomparable strength to weight ratio, temperature stability, and thermal conductivity. We CNC machine and heat treat our cylinder girdles for precise fitment and optimal function.

 The key to performance and durability increases lie in limiting each individual cylinder assembly's movement. During the combustion cycle on a standard engine, the cylinder displaces in reference to the engine case because of the long moment arm that is established by only affixing the cylinder at the base. This lack of rigidity allows the cylinder to move with the forces being exerted upon it by the rotating assembly and combustion process. By locking the cylinders in place and limiting the cylinder movement, combustion efficiency is improved, resulting in a greater power output most noticeable on engines running extremely high combustion pressures and/or high RPM. Also, by limiting individual cylinder movement, fretting-prone areas of the crankcase are reduced due to the increase in torsional stability of the entire engine assembly.


But the improvement in cycle efficiency is just a happy by-product of the design intent - to produce a more durable performance engine assembly. Have you wondered why engine baffling panels are split between cylinders? Sure thermal expansion is an easy answer, but in actuality it is necessary because the large amount of cylinder movement quickly leads to stress fractures in a solid baffle plate. Or have you seen incidences of cylinder base studs cracking or breaking off completely? That is due to the cylinder base rocking with respect the case. In high output engines, this cycling of pressure on the studs leads to fatigue and failure.

We have a great deal of test data showing the comparison in movement between standard (unsupported) cylinders and cylinders utilizing our girdles. We utilize data acquisition components to measure acceleration data in all 3 axes at sample rates up to 48kHz (that's approximately 1 data sample for each 0.25 degrees of crankshaft rotation at operating RPM). This data helped us progress the design along with CAD-based finite element analysis to obtain ultimate strength without unnecessary mass.

Full Load/2500 RPM Cylinder Displacement Tests, Before (↑) & After (↓) Girdle Installation

We incorporated additional benefits into the design of our girdles. Bosses in the lower section of the girdle can be used one of two ways. When utilizing our cylinders that have been modified for oil-cooled exhaust valve guides, these bosses can be used as additional oil return ports. Alternatively, these bosses can be machined to accept nozzles to spray oil directly on the exhaust valve stem and spring to reduce valve operating temperature in high-CR or turbocharged applications.

 Cylinder movement also affects the valve lift profile in that the stock hydraulic unit has difficulty accommodating the continuously changing lash. By limiting the movement of the top end, valvetrain development can progress in a methodical way, rather than guessing at how cylinder movement will affect the valve timing and lift curve across the range of RPM and load points. 

Our girdles are CNC machined to fit the engine properly. The top and side surface contours have been machined to mimic the stock valve cover outline so that existing baffling can be be re-used with only modifications in the center bridge area. 

The downside to this kit is that with an increase in engine strength also comes an increase in engine weight and width. The girdle castings are approximately 1/8" taller than the standard Lycoming rocker covers, so this needs to be taken into account on ultra tightly cowled aircraft. And while we have done our best to maximize the design using FEA and stress testing, there is a slight weight increase over the stamped steel rocker covers. 

 The chart below details the weights of the various configurations:

Engine Standard Components (pounds) Top Cylinder Girdle,   Basic Kit (pounds) Top Cylinder Girdle, High-Power Kit (pounds)
IO-320/360, Parallel-Valve 2.0 3.8 4.5
IO-540, Parallel-Valve 2.9 4.9 6.4



 The Top Cylinder Girdles are available as a "Basic" kit which includes the set of Girdles, mounting hardware and seals.


Type Price
Lycoming IO-320/360 Parallel-Valve Girdle, Basic Kit $1,367.00
Lycoming IO-540 Parallel-Valve Girdle, Basic Kit $1,903.00


The girdles are supplied with a raw magnesium finish. We have sealed and coated the girdles to prevent future corrosion. You may leave the girdles as they are supplied, or you can paint them to match your engine's color scheme.

Installation instructions for our Top Cylinder Girdles can be found by clicking on the "Information" button on the left side of our website.


Important:  Our Top Cylinder Girdles have been designed and manufactured to properly fit Factory Lycoming cylinder assemblies. Because of differences in other manufacturers' products (ECI, Superior), we only guarantee fitment on OEM Lycoming cylinders.


As with all of our performance products, our top cylinder girdle assemblies are intended for use on Experimental aircraft only.










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