Upgraded Polyurethane Engine Mounts and Suspension Bushings
Replacing Engine and Suspension mounts and bushings with harder polyurethane is a common upgrade for most tuners. OEM mounts and bushings are generally designed to keep Noise, Vibration, and Harshness from reaching the passengers (N/V/H for short). When you start making more power than stock or beginning to get into performance driving you may find that the stock rubber bits aren't up to the task anymore. A common sore spot on high power or even just bolt on Civics has been the rear lower engine mount, or lower torque mount. The stock one is designed to minimize N/V/H but once pushed you may find the lack of support effecting shifting and causing the exhaust to bang against other components. Wheel hop is also an issue on high power FWD cars.
The soft compliance bushings in the suspension can also lead to poor steering feel and for a performance application, reducing the degree of movement or squirm of various bushings provides a more direct and immediate suspension and steering response and superior maintaining of wheel alignment angles during suspension travel.
Why do you need upgraded mounts?
Once you start modding your car and adding power you may run into some small issues. One of the more common issues has been the down pipe and exhaust banging against the frame. The soft OEM mounts can't control the motion of the engine and the small clearance is used up by the larger diameter performance parts. Sloppy shifting has also been attributed to the stock mounts allowing parts to shift under load. If you engage in "spirited driving" these issues may become more evident to you. Upgrading the rear engine mount has solved the exhaust bang issue for a lot of people. The engine will move around a lot on the stock mounts. Just watch the video below of a stock k24.
The real issue: WHEEL HOP
On high power FWD cars a phenomenon known as "wheel hop" is a very real issue. Basically the soft suspension and chassis mounts allow enough flex that under heavy load, ex: a hard launch, the power is transmitted not to the wheels but into the bushings themselves. Think of them as very hard springs. Once they get twisted up enough, they release that energy and drive the wheels. This also results in the wheels momentarily changing angles, toe, and losing and then regaining traction. This causes the wheel to "hop" and bang up and down as it moves in the wheel well. This is not only bad for acceleration, but bad for your car. You will know when it happens as it is pretty loud and you will think things are breaking. They are trying to. You need to control the motion of the wheel in respect to the chassis. The stock mounts are usually too soft to control this. This is where upgraded aftermarket mounts are needed and useful.
Wheel hop can lead to broken drivetrain parts, including axles and transmissions on a front-wheel-drive car. If your car wheel hops - get it fixed! There are a lot of claimed solutions and people generally attack the wrong parts first. We want to address the parts that are allowing this motion to happen. This means chassis mounts and suspension bushings. On the Civics, generally replacing the engine mounts solves the problem pretty well. You could look into replacing the compliance bushings on the front lower control arms but for the most part the rear engine mount alone is enough. You will read about people trying to solve wheel hop through traction bars, springs, struts, and sway bars. It is not the fix. Address your bushings and mounts.
Is wheel hop really an issue? YES.
Wheel hop occurs when the wheel goes quickly between gripping and slipping when you accelerate hard. It will cause your car to violently shake, vibrate, and produce a loud thumping noise. High RPM launches can cause this when you don't maintain a little wheelspin and are allowing the tire to momentarily catch. you need to have good throttle control to prevent it. The problem with wheel hop is not the loss of power and acceleration but that the hopping action can and will damage drivetrain parts. The feeling is just as bad as the actual effect it has on your car.
Whats the fix? :
Several aftermarket companies offer upgraded mounts. This usually means a harder rubber mount. Rubber and polyurethane "hardness" or "stiffness" is measured on a scale called Shore A. It's also referred to as Durometer.
When it comes to dampening, urethane durometer is very important, as well as volume of urethane, and quality of urethane. Replacing your engine, suspension, or other mounts and bushings require more than picking a bushing durometer.
Durometer, volume of urethane, and grade of urethane (or other material) all directly influence the transfer of power to the wheels, the transfer of N/V/H levels to the passengers, and the life of the urethane. The ideal polyurethane would put all of the power to the wheels and not transmit any additional N/V/H to the passenger cabin. It would also never wear out! Currently this magic material doesn't exist. There are compromises to be made and improvements in the driving experience to be had without ruining your car.
Urethane Explained:
What the heck do those numbers mean?
What is Durometer? Durometer is the hardness value of the polyurethane. To determine the hardness, stiffness, or resistance of indentation, a Shore Durometer gauge is used to penetrate the urethane. The Type A hardness scale ranges from 0 to 100. Most aftermarket urethane engine mounts are between 60A and 90A.
Stock parts and mounts are typically very very soft. So what happens when the durometer is increased?
- N/V/H increases
- Performance increases from the lack of "softness" and movement from the mounts
Wheel hop is a real issue in the Civic chassis. Harder engine and torque mounts help to quell this.
As engine output is increased, so should the durometer of the bushing.
How does engine output or horsepower relate to urethane? The more load placed on the engine mount, the harder the urethane should be. Choosing the correct urethane for your engine output and driving characteristics will directly relate to the lifespan of the urethane as well.
How do I get the most power to the wheels? If your primary goal is power, go with a high durometer urethane option. The harder the urethane, the least amount of power lost in the drivetrain and the most amount of power transferred to the wheels. With a high durometer value comes more NVH!
Power and urethane durometer guidelines:
Power levels: 220-325 WHP
Use: Street
Driving: Normal, DD, Auto-X, "Dragon runs"
NVH: More than stock but not unbearable
Durometer: 60A +/-5
Power Level: 300-500WHP
Use: Street/Track
Driving: Aggressive, "Spirited"
NVH: Moderate, borderline tough for a DD
Durometer: 70A / 80A range
Power Lever: 500+?
Use: Street/Track
Driving: Aggressive/Drag strip
NVH: Awful, if you have to DD your car at all. (personal opinion)
Durometer: 90A+
Break in time: Be ready to put up with a decent break in period.
Any upgraded urethane part is going to have a break in period. Generally the parts will start out very hard and "soften" to their intended hardness level. This will result in a lot of N/V/H initially. Different parts and durometers will take longer than others to break in fully. My experience so far is that 300 miles on one upper torque mount and it is no where near broken in yet. Better, but still very very loud and rattle inducing. You may find that even one mount on the softest available durometer is too much for you. Just be prepared for increased noise and vibration. Give it a little time before you decide to keep them or remove them. Don't replace them right before a long trip unless you want a headache. Personal experience talking here.
Post your experiences or questions and ill try to answer them as best I can.
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