The most common advice given to a new MAZDASPEED3 owner interested in modifying their car is to replace the factory motor mounts, especially the rear motor mount. Having received this advice myself I decided to do some research and pass it on.
What and where are these motor mounts?
Motor mounts are what connect your engine to the frame of your vehicle. They are made of metal and always have some sort of bushing insert. The metal gives the mount the strength to carry the weight of the engine, and the bushing helps protect the engine from frame movement (over sharp bumps ect.) and the frame from engine vibration.
MAZDASPEED3 has 3 factory mount locations (pictured below). They are the:
- Rear Motor Mount (RMM)
- Transmission Mount (Driver Side)
- Passenger-Side Motor Mount (PMM)
The Mazdaspeed3 actually only has two motor mounts. They are the transmission (Drivers Side) mount and the passenger-side mount. The rear motor mount isn’t really a mount. It doesn’t support the engine’s weight. It is a type of torque strap which is a third contact point with the car’s frame that works to mitigate the rotational energy (torque) of the engine and improve power delivery. However, you’ll hear it most often referred to as the rear motor mount.
The firmness of a mount (including the torque strap) is dictated by the bushing material’s size, shape, and durometer. The higher the durometer, the stiffer the bushing. There are also a variety of bushing materials which include rubber, urethane, and polyurethane. It’s important to note that durometer is a measurement of the strength of the SUBSTANCE, independent from it’s current form factor (size and shape). This means that two mounts with equal durometer bushings yet different bushing form factors will have DIFFERENT strength properties.
Why should I replace my motor mounts?
Mazda did not include mounts of sufficient strength with the MAZDASPEED3. In fact, they used the same mounts that they use the Mazda 3, a car with 48% less torque. This causes the engine to move significantly in the engine compartment, as evident in the video below.
All this engine movement, also known as lash, can cause problems for your car, and have a negative impact on your driving experience. During launches and hard acceleration the engine’s movement can actually lift one of the wheels off the ground, an effect known as wheel hop. The negative impacts of wheel hop are many. Besides the obvious lack of traction, wheel hop puts unnecessary strain on many drive train components including the axles, differential, and transmission. Excessive drive train movement also makes shifting under hard acceleration difficult to impossible due to the inability of the shifter to line up gears.
In the MAZDASPEED3 the main culprit for engine lash is the rear motor mount. Below are two images of rear motor mounts. The first is an image of the stock mount. Notice the holes in the bushing? Mazda doesn’t even include a solid bushing in it’s mount. The second image is of an aftermarket mount from CP-E. The difference in strength between the two mounts is self-evident!
Stock Rear Motor Mount
Aftermarket Rear Motor Mount from CP-E
Why didn’t Mazda include stronger mounts in the MAZDASPEED3?
This is a question asked by many people, and has a few answers:
First would undoubtedly be cost and ease of production. While sporty, the MAZDASPEED3 is still just a souped up Mazda3, so they share many of the same parts. For every part that is different, costs increase as well as method of production. And for a bang-for-your-buck car such as the MAZDASPEED3, keeping cost down is very important.
Second, and of importance to you as a current owner, is ride comfort. The firmer the motor mounts, the more vibrations and noises created by the engine are transmitted into the cabin. So choosing motor mount strength is a balance between reducing engine movement and overall cabin comfort. This leads to the main drawback of upgrading your motor mounts.
Your cabin comfort can suffer minimally to dramatically depending on which mounts you replace and how firm they are. Replacing any mount will increase the amount of vibrations transmitted into the cabin. Any loose trim will start to make noise, and any trim that isn’t loose will be soon enough! In the MAZDASPEED3 replacing the passenger side motor mount will transmit a large amount of engine noise because of the mounts proximity to the engine’s belt system and head. Also, replacing the driver’s side (transmission) mount will transmit a large amount of mechanical noise from the transmission.
- Reduced Wheel Hop
- Improved Power Delivery
- Increased Overall Feeling of Solidness
- Increased Shifter Accuracy
- Increased Cabin Vibration
- Increased Cabin Noise From Road, Engine, and Transmission
- Annoyed Passengers Who Don’t Share Your Enthusiasm
Of course, if you’re like me, you’ll read the cons as:
- Free Back Massage
- Listening To Your Car Be Awesome
- Lame People Who Don’t Deserve To Be In Your Car Anyways
So now that you’re good and excited about replacing your motor mounts you need to know what to buy and where, right? These buyer’s guides will help you narrow down your options: