My car's a manual, but I felt more than one difference with an upgraded RMM. Most people on the ST forum will tell you that it's the first mod you should do.
First, the stock one is really soft. Overly so, even for base model automatics. It's about zeroing NVH in brand new cars. I certainly remember how smooth the car felt when it was new. NO vibration, through the wheel, the seat, the shift knob. None. Ford spent a lot of time and money making the Fiesta a quiet, comfortable car for its size and price point.
After about 10,000 miles, the NVH was still plush as a Cadillac. I also had to give it a few milliseconds between shifts, especially when giving it the beans, because it's way too soft for any spirited driving. It's made of rubber. It's just going to get softer and softer, until there's too much play for anything but super smooth mileage jockey-type driving. Not my jam.
Changing it benefitted my car in more than one way.
First, of course, it reduced engine movement in relation to the drivetrain. I can go for the next gear sooner, and snick it right in there, losing fewer rpms between shifts.
Second, it reduced wheel hop when I'm really getting on it. My car always struggles to get grip when I pin it in 1st or 2nd, and spins in 3rd a little, too. It's the curse of FWD cars. They just aren't drag racers. They're handlers.
Third, it reduced torque steer. My car makes over 240 tq, and it starts early in the rev range. This is more noticeable when stomping on it, because it tracks straighter, and it also helps when I'm shifting in corners and such, but it's there all the time.
It didn't eliminate wheel hop and torque steer, but the difference is major. It just puts the power down better, in every way. The car is much more confident in itself. 0-60 is definitely improved with that single part.
The only downside is that you don't have that perfectly dead-feeling NVH. There is a tiny bit of vibration through the wheel at idle, and it's more noticeable with the AC on. There's a little between 1000-1100 taking off in 1st gear. When I'm rolling, it's not noticeable at all.
Let me put it in perspective. If I start the car, I have to really try to notice it to notice vibration. It smooths out a little after a thousand miles or so, too.
Any vibrations I can feel when I'm stopped are completely cancelled out if I'm stopped next to a semi, or another big diesel. Or if someone's cranking their big stereo, or there's some other noise.
Other vehicles vibrate my car more than my car ever will, even if I'm playing music and have it turned up. When I'm at speed, there's no change.
Your car is a lot different, but there would still be a difference in power to the ground. The added benefit is it's a more durable part, and you could take it off and sell it if your car gets ruined.
If I had a DCT Fiesta, I'd get this before an intake or exhaust. Best mod there is, in terms of bang for the buck. It's even made well. I'm glad they're available.
