Fabricating Custom Engine Mounts for the Mazda RX8 Sports Car

Customizing Engine Mounts for the RX8

The Mazda RX8 is a unique sports car with a rotary engine design that allows it to rev higher and produce more power from a smaller, lighter engine. However, the design of the Renesis rotary engine also presents some challenges when performing an engine swap or modification. One key consideration is fabricating custom engine mounts to correctly position the engine and support its weight.

Assessing the RX8's Factory Engine Mounts

Before fabricating custom mounts, it's helpful to understand the factory setup. The RX8's engine and transmission are mounted on a subframe that bolts to the chassis. Rubber mounts isolate vibrations and shock loads between the powertrain assembly and subframe. The rear mount helps stabilize the transmission and is typically very stiff.

When performing an engine swap, the factory mounts may or may not work with the new engine. Measurements need to be taken to determine proper positioning, height, and inclination angles of the new engine. Aftermarket mount kits are available for some popular swap configurations, such as a GM LS V8. Otherwise, custom mounts will need to be fabricated.

Design Considerations for Custom RX8 Engine Mounts

Several important factors go into designing custom engine mounts for the RX8:

• Engine weight - Heavier engines require stiffer mounts and additional support
• Compatibility with the subframe and chassis mounting points
• Maintenance of proper steering rack and suspension clearance
• Achieving the correct engine inclination angle
• Managing vibration isolation and engine movement

The subframe and chassis mounting points are essentially fixed, so the mount design has to adapt to those constraints. Rubber or polyurethane mounts allow some engine movement but also transmit more vibration. Getting the angle of the engine correct ensures proper alignment of components like oil and water pumps.

Fabricating Custom Mounts for the RX8

Fabricating fully custom engine mounts requires some skill with metalworking tools. The basic process involves:

1. Designing mounts in CAD software based on measurement data
2. Cutting mount plates from steel or aluminum plate
3. Drilling holes for mounting bolts and studs
4. Welding threaded bungs, spacers, and other mounting provisions
5. Machining surfaces flat and smooth
6. Sourcing and installing rubber or polyurethane isolators
7. Final test fitting and adjustments

Tack welds are helpful for test fitting parts before completing welds. Having an adjustable mount makes dialing-in the engine inclination easier. Good penetration from welding is critical for structural integrity. If possible, vibration damping material like Sorbothane can be added between metal parts.

Installing Custom Engine Mounts in an RX8

Once custom engine mounts for the RX8 are fabricated, the installation process can begin. This involves:

1. Safely supporting the engine/transmission
2. Removing the factory mounts
3. Lowering the engine/transmission onto the new mounts
4. Installing and tightening all fasteners to proper torque specs
5. Checking fitment and angles
6. Connecting components like exhaust and shift linkage

Having an assistant is very helpful for guiding the engine down safely. Starting fasteners by hand prevents cross threading. Double checking measurements after install is critical. Initial startup and testing should be done carefully in case any issues are found with the mounts.

Troubleshooting Custom RX8 Engine Mounts

Diagnosing issues with custom engine mounts involves understanding their failure modes. Common problems include:

• Noises or clunking from loose mounts
• Visible cracks or tearing of the rubber isolators
• Engine leaning excessively to one side
• Excessive vibration felt inside the cabin

Loose mounts that allow engine movement can be fixed by torquing or re-tightening fasteners. Worn isolators will need replacement. An engine leaning to one side indicates a problem with that mount's placement or fastening. Too much vibration may require stiffer isolator materials.

Conclusion

Fabricating custom engine mounts for the RX8 takes planning, measurement, and solid metalworking skills. Mounts have to properly position the engine, withstand its weight and torsional forces, allow some movement from rubber isolators, and mitigate vibration. Carefully installing and testing custom mounts is critical before enjoying full performance from an RX8 engine swap.

FAQs

What materials are best for custom RX8 engine mounts?

Steel and aluminum plates or brackets are commonly used for fabricating mounts. For the isolator, rubber, polyurethane, and Sorbothane provide good vibration damping. Rubber tends to be the most flexible while polyurethane is more durable and offers some adjustability.

Can I install LS engine mounts in an RX8?

Some companies sell swap mount kits to install GM LS V8 engines into the RX8 using the factory subframe mounting points. This can save fab time but measurements need to be checked for proper positioning and fit.

Is welding required to make custom engine mounts?

In most cases, welding is critical to manufacturing custom engine mounts as it permanently joins steel/aluminum parts into a structurally rigid component. Welds also have to support the weight and forces from the powertrain.

Should I get an adjustable rear engine mount?

An adjustable rear mount makes it simpler to achieve the correct engine inclination angle during test fitting. It allows more positioning flexibility compared to a fixed custom mount. Just remember to securely lock it down after final alignment.