Long-Term KTM RC390: Mivv Ghibli Exhaust System Installation

Less weight, more power, and better sound with a Mivv muffler.

MIVV Ghibli exhaust for the KTM RC390
The Mivv breaks muffling duties up between the actual muffler and a pre-chamber that passes through the swingarm. Like the hanger? It’s super custom.©Motorcyclist

WRIST: Ari Henning
MSRP (2015): $5,499
MILES: 3,127
MPG: n/a
MODS: Mivv Ghibli exhaust

An aftermarket pipe is usually at the top of every rider’s list of desired mods. I know it was near the top of mine! I love the look of the RC’s under-engine exhaust setup, but the stock pipe is heavy and sewing-machine quiet. Since the RC390 is being raced I’m keen to shed whatever weight I can, plus, I want my competitors to hear me coming!

After seeing and hearing the pipes that Akrapovic and Yoshimura have for the RC390 on other peoples' bikes, I decided to try a Mivv muffler, secured through MNNTHBX (mnnthbx.com). Mivv is an Italian company and it has several pipe variations available for the RC and the Duke. The Ghibli I chose is a sleek setup, with a curved muffler ringed with beautiful welds reminiscent of a MotoGP pipe. For $505, the Mivv is priced much lower than the dual-can undertail Yoshimura ($799) system or the Akrapovic pipe ($899) that comes on the RC390 Cup bikes.

It sounds great, too. With the sound-suppressor tip removed the Ghibli has a deep sound with good tone. Take a listen for yourself.

The Mivv was one of the only parts I didn't install myself. Instead, Motorcyclist's Assistant Editor, Will Steenrod put it on for me, and he wasn't too happy about it. As with some other parts (I'm thinking of the Tyga rearsets I put on), installation is complicated by the RC's peculiar design. In this case the shock had to be removed and the swingarm manipulated to get the stock breadbox/muffler assembly removed.

Once the stock pipe was ditched Will said the Mivv went on easily, though he encountered an issue with the muffler end cap, which you install in place of the optional sound-suppressor tip. Will said the tack welds on the back of the cap prevented the cap from sitting flush, so he had to file the welds down so the cap would sit flat. The only other issue we had was that the muffler bracket that’s provided didn’t work with my Tyga rearsets, so I had to bend my own hanger from flat iron. MNNTHBX now offers an alternative muffler bracket for riders with aftermarket rearsets.

KTM RC390 stock muffler
The stock muffler is a hideous little thing. Good thing it lives behind the RC’s belly pan. This one is going to live on the shelf from now on. And look at that tiny outlet!©Motorcyclist

The RC's fueling is crazy lean from the factory, so I added a Power Commander V (powercommander.com) at the same time, as well as a K&N air filter (knfilters.com) for good measure. With the pipe and a base map on the Power Commander, the RC picked up an easy 2 horsepower, jumping from 41 to 43 hp. And compared to the stock steel muffler box thing, the Mivv was over 5 pounds lighter.

Less weight, more power, and better sound. Everything I wanted! What I didn’t want (or expect) was a reduction in right-side cornering clearance, a fact I learned when I took the RC390 back to the track. Adding rear ride height bought me a few more degrees of lean angle, but I still managed to grind through the lower connector pipe during a race weekend. Damn! I took the exhaust to my local welder for repair, and I also had him remove a 20mm-long section of tubing from just inboard the final bend so the whole mid-pipe and muffler assembly is tucked in closer to the swingarm.

I haven’t dragged the pipe since, and I’ve provided feedback to Mivv though MNNTHBX in hopes that they’ll update the pipe’s design. It’s fair to say that reduced cornering clearance is a glaring issue on a pipe designed for racing, but I’ve heard that the Akrapovic exhaust has the same issue. Yoshimura’s under-tail system isn’t going to touch down unless a bunch of other stuff already has (as in you’ve crashed), and even then the mufflers are fairly well protected. I know of several racers who have chosen the Yosh system based on that fact alone.