Does The Malossi Exhaust Cause The BV350 To Run Lean?

There’s an old saying that a lie can travel halfway around the world while the truth is still putting its boots on. In the world of vehicle tuning, that misinformation is usually travelling at warp speed across a dozen internet forums, posted by someone called ‘DaveRS_Turbo’ who once saw a picture of an engine.

Following on from my last post about clearing the engine fault light, I discovered my little diagnostic scanner could do a lot more. So, I set about putting a question to rest that's been bugging me for ages: does the Malossi exhaust I run on my Piaggio Beverly 350 cause it to run lean?

The Contradiction

Malossi themselves claim that all their kit for the BV350, including the RX exhaust I have, works fine without a remap. They say the bike can cope with the tendency for aftermarket "performance" exhausts to cause a lean mixture. This is a statement peddled by many a forum dweller, though when pushed for hard evidence they tend to go quiet.

The thing is, Malossi also sell a little device called the Force Master, which remaps the bike to work perfectly with their products. But if you don't need a remap, why are they selling this magic box? My skeptical eyebrow was well and truly raised.

I was tired of opinions and marketing bollox. I wanted facts and figures. And thanks to my recent adventures with the scanner gadget, I had the tools to get them.

The (Supposedly) Simple Plan

The plan was simple, scientific even. I would test the bike with both the stock and the Malossi exhausts back-to-back.

One thing worth mentioning: this isn't a stock bike; it's already running a Malossi air filter and variator kit. This test was purely to isolate what, if any, difference the exhaust alone makes to an already-upgraded setup.

I’d record the engine data, specifically the Short Term Fuel Trim (STFT). This is the bike's computer telling you in real-time if it’s having to add or subtract fuel. A positive number means it’s adding fuel to fix a lean mix. A negative number means it's taking fuel away to fix a rich one. Simple.

At least, the plan was simple. The execution, as is traditional here at Mostly Bollox, was a complete farce.

Attempt One: The Android Sabotage

With the stock exhaust fitted, I set out on a quiet Sunday morning. The roads were clear, the bike was warm. I fired up a car scanner app on my spare Android phone, hit record, and completed a perfect test run, including my little 40-60mph roll-on tests. I got home, exported the data, and opened the file. It was a beautiful, detailed log… of my GPS coordinates. And nothing else. Turns out, if you have “record location data” ticked, the app assumes you couldn’t possibly want to record anything else. Like, you know, engine data. Annoying.

Attempt Two: The Sleepy Apple Attack

Just as I was about to go again, the heavens opened. Proper Northern Irish rain, too dangerous for testing. I retreated indoors for a cup of tea and a sulk. Later, a break in the weather! I switched to the iPhone, forking out for the Pro version of the app since the free one doesn’t record data. I set it all up, put the phone safely under the seat, and set off. I completed another perfect run but thought to check the data before heading home. Just as well. The app had recorded a grand total of 11 seconds before the phone, tucked away in the dark, had simply gone to sleep, stopping the recording. Bollox!

Attempt Three: The Final Battle

Right. No more messing about. I set the iPhone’s auto-lock to “Never” and mounted it to the handlebars where I could keep a paranoid eye on it. I redid the stock exhaust run, capturing a perfect log file this time. Then it was back to the garage, spanners out, swap to the Malossi pipe, and do the exact same run again.

Finally, I had the data. Two big, beautiful spreadsheets full of numbers.

The Verdict

After a lot of staring at spreadsheets, I fired it all into my trusty AI assistant. The truth finally emerged. Here’s the key metric; the average Short Term Fuel Trim during a steady 60mph cruise:

• Stock Exhaust: +1.15%
• Malossi Exhaust: +5.35%

So, what's the verdict? Were Malossi and the forum dwellers right? Well, yes and no. Kinda.

The data is clear: the Malossi exhaust absolutely makes the bike run leaner. Anyone who says otherwise is, according to my data, wrong. However, the bike's ECU is smart enough to compensate perfectly by adding more fuel, in this case, an extra 4.25% over stock.

So, is it a problem? Honestly, no. Anything within about +/-10% is considered perfectly fine, and the bike's computer is clearly doing its job brilliantly. The only real-world downside is a slight hit to your fuel economy.

For now, I’m keeping the Malossi pipe on. I've grown to love the sound, and the data shows it’s perfectly safe. But that little Malossi Force Master box is now whispering my name. The urge to get that fuel trim back to a perfect zero is a powerful one for a tinkerer. I just need to save the pennies first.

It was a frustrating day, but I got there. I swapped opinions for data, and that, for me, is a massive win.