Do you need a Power Commander for full exhaust on the Kawasaki Ninja 400?

A lot of people ask about slip-on exhaust vs full exhaust, and whether or not you need a fuel controller (power commander, bazzaz, ECU flash) when you install a slipon or full system exhaust. So let’s cover that with some real data. Different bikes vary a bit because of where the stock restriction, muffler, and catalytic converter are in the exhaust, so here’s some info as it relates specifically to the Ninja 400. The Ninja 400 has the main sound restriction in the slipon muffler, and the catalytic converter is part of the midpipe of the header. This means that you can actually pick up some small gains by changing the slipon, but more importantly, you can dramatically change the sound with only a slipon. That’s nice for the street guys who want to make the bike louder.

As you can see below, I didn’t get an AFR reading on the bone stock bike with stock exhaust because there’s a restrictor plate in the exhaust that prevents me from shoving my AFR sniffer down the pipe, but once a slipon is installed, we can get a decent AFR reading while the header is still stock and the catalytic converter is still installed. See the red line below, with the slipon, you can see there’s very little change compared to stock except at the top of the RPM range where power increases slightly and you can also see the AFR curve rise slightly. I’m going to make the assumption that the stock bike with stock muffler would follow a pretty similar AFR line except it wouldn’t rise so much at the top and would probably stay pretty consistent across the power band around 13.2-13.4 AFR just like the red line. That’s the small improvement in air flow you get from a slip-on exhaust.

You can also see how crazy up and down the AFR line looks below 8000 RPM and super lean below 6000 RPM where emissions tests are done. This is where a lot of gains can be had by optimizing the fuel and ignition timing when you aren’t worried about emissions. Now look at the green line, which is the bike with an Akrapovic full system installed and no fuel controller. You can see the bike definitely makes more power across the board, but the AFR line also goes leaner everywhere. What does this mean? A leaner burn will burn hotter, and I’d say if you ask pretty much any tuner across the world, a bike that runs above 13.5 in the power band is dangerously lean and not at all recommended. Not only will the engine temperature rise faster, but if the combustion chamber gets hot enough, it can cause detonation or melt the pistons, rings, head, or cylinder walls. Especially if you’re riding it aggressively or on the race track and keeping it hot for longer periods of time. Not good.

In this graph below, I did a quick correction to the 100% throttle using a Bazzaz Z-Fi to show what happens when you adjust the fuel when an exhaust is installed.  Look at the pink line below, you can see the AFR brought back down to 12.9-13.0 in the power band. The bike makes great power, the same or better everywhere compared to without the tune, and the power curve is smoother and a little stronger in places. The engine will run much cooler and last longer, especially when ridden hard at high RPMS. This is why it’s always recommended to correct fuel when running a full exhaust.