Saturday, June 23, 2018
DriveWerks

[Project Fiesta] Stiff Arm the Party

Few cars are perfect right off the production line. Each and every car has its own design quirks which lead to aftermarket solutions. In the case of Finn the Fiesta, Ford Motor Company thought it was A-ok to let the motor twist and shout.

The Westermeister has been driving his Fiesta ST for a little over six months, so things have broken in by now. As seen in a previous write-up, the Fiesta received a short shifter not long after being purchased. Once the miles started to add up though, Wes noticed the infamous Fiesta ST knocking sound upon acceleration. For non-FiST drivers, this noise is caused when the transverse mounted engine hits the firewall. The prime suspect is the rear motor mount. It’s a flexible rubber mount that was designed with NVH in mind. The problem however isn’t that it’s rubber, but rather that it has voids which allow excessive deflection. Adding insult to injury, the stock mount is also shared with the base model Fiesta. Unlike its tamer sibling, the ST engine is pumping out nearly 80 extra horses. In other words, the stock rear motor mount isn’t going to last to long in this arena.

Adding Beef to the Veggie Tray

The Fiesta ST has a large following, so plenty of companies are making performance parts for the Blue Oval’s tiny hot hatch. In the case of the rear motor mount, there’s two popular options to choose from. The most common is COBB Tuning (known widely in the Subaru community), and then there’s also the famed Mountune. Both companies produce quality parts, but the Mountune parts tend to be more warranty friendly. Wes’s car is still under the factory warranty, so sticking with Ford approved parts seemed like the logical choice.

The Mountune rear motor mount was ordered for $150 (including shipping). Once the motor mount arrived in the mail, it was evident this was a heavy duty part. In addition to the physical mount is a set of install instructions, as well as lithium grease to keep the polyurethane bushings quiet. As a side note, the poly bushings are made by Powerflex, so you know the fit and finish will be up to snuff.

Installing the Mountune unit was very straight forward. After getting the car on jack stands, I slid my lazy self under the car with plenty of room to work. The rear motor mount sits fairly low and isn’t obstructed by anything. The mount itself is only held on by two 13mm bolts, but there’s a couple of supporting brackets held on by four 13mm nuts, so they have to come off before the motor mount bolts do. Once everything is disassembled, the mount will slide out with one of the brackets attached.

Mountune’s online video will tell you that you’ll need to drill the bracket out of the stock bushing, but truth be told, the bracket is simply press fit into place. A hammer and small pry bar combo made quick work of this. With the bracket freed, it was time to get the new mount ready for the line of duty.

Install of the new mount was very similar to removal of the stock mount. Using the supplied lithium grease, we lathered up the polyurethane bushings to prevent any squeaking, then set about putting the new mount into position. There’s an order to installing all the brackets and supplied washers, but the instructions keep the process organized.

Return for a Romp

With everything reassembled and properly torqued, Wes took a quick spin around the neighborhood to confirm no parts were seen flying off the car in the rear view mirror. We let a week go by so the motor mount could get settled in its new home. Once the next weekend rolled around, Fiesta Finn went back up on jack stands to receive a follow-up exam. The bolts were still torqued, meaning we could finally test if the mount was worth the money.

As mentioned before, the stock rubber motor mount would let the engine rotate too much, ultimately knocking against the firewall. An aggressive launch onto a freeway on-ramp immediately warranted the purchase. No engine banging on the firewall saying hello, just the metallic marshmallow converting 16 pounds of boost into kinetic energy.

It’s safe to say that the feisty Fiesta now accelerates with little drama, probably because the stiffer mount eliminated much of the wheel hop associated with front wheel drive cars. Also solved is the crap shoot of the 1st-to-2nd shift caused by the flexible stock mount. With these issues put to rest, the power can quickly and efficiently make its way to the ground.

Thanks to the new Mountune mount, enthusiastic driving is noticeably more predictable and confidence inspiring. Best of all, there’s virtually no increase in NVH. If you only do one modification to your FiST, an upgraded rear motor mount is probably the top contender. Reasonably priced, easy to install, and instant results. Ziggy would probably describe it along the lines of “Wam, Bam, Thank You Ma’am.” Wait…who’s got the eight-track player?

 

-JC

 

Interested in an upgraded rear motor mount for your Fiesta ST? Here’s where ours came from:

Mountune Fiesta Rear Motor Mount

 

 

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