Gimmick or a truly affordable hack? More importantly, what does it really do?

The vast majority of us don’t hold automobile engineering degrees. We know a lot about our motorcycles, but if we struggle to make it through a corner, most of us can’t pinpoint whether that is because of rake/trail, suspension setup, tyres, bike geometry or just rider skill. What we do, instead, is get used to it and call it a ‘quirk’. But is it, really? Or is it a solvable issue? What about snatchy throttles? Is it ‘aggressive throttle response’ or ‘man, something feels off’?

I’m no stranger to the above phenomenon. I adore my 2016 Triumph Street Twin, but since the beginning, I felt it stuttered a little at lower revs. Don’t get me wrong, it had more than enough torque; it just wasn’t as smooth as I expected. But I got used to it, until the end of 2019 when I went all out with performance products from TEC Bike Parts- a full system 2-into-1 exhaust, and a new camshaft. Articles on both are coming soon, but today, I want to talk about my biggest gripe with the upgrades- the throttle response. It became impossible to ride smoothly at lower revs, as it had transformed a smooth bike into an incredibly jerky one. Very annoying. And in the absence of a dedicated tuner in Bombay, I decided to try out the Booster Plug, which claimed to solve this issue.

I’m going to save you the suspense- it worked. Brilliantly. If you don’t care how, and just want a smoother stock or modified bike, just get one. But if you’re interested to know more, then read on because I’ve tried to simplify it to the best of my ability.

Let’s start with a few terms you need to be familiar with.

Air/Fuel Ratio

The amount of air required to completely burn one unit of fuel. For eg a 14.7:1 A/F ratio (The actual ratio for petrol) indicates 14.7 units of air are required to completely burn off one unit of fuel. A rich A/F Ratio is one where more fuel than ideal is added, which means after combustion you will still have some excess unburnt fuel remaining. A lean A/F Ratio is one where less fuel than ideal is added, which means after combustion you will still have some excess unburnt air remaining.

ECU- Basic Fuel Map

Motorcycles have evolved into complex machines, with the (much scoffed at) reliance on computers actually resulting in staggering improvements. The Engine Control Unit (ECU) tops that list, and plays an important role in managing the aforementioned A/F Ratio. Since the advent of fuel injection, ECUs have determined how much fuel to spray into a cylinder for optimum combustion through basic fuel maps. This reads data from a throttle position sensor and an RPM sensor. Depending on the amount of throttle applied and the engine speed, an appropriate amount of fuel is sprayed in. But that’s not all it takes to get the perfect mixture. In addition to this, an oil temperature sensor detects whether the engine is internally cold or has warmed up, and adjusts the fuel input to compensate. The next data the ECU receives is from an Air Pressure Sensor, which allows the A/F ratio to adapt to different altitudes. And finally, the ECU receives information from the Air Intake Temperature sensor, which influences the fuel input compensation for cold or warm riding conditions. When it gets cold, air gets denser and thus more fuel is required for complete combustion. When all of the data is fed into the ECU, the complete equation determines the amount of fuel needed for effective combustion.

ECU- Closed Loop

Unfortunately, the above scenario doesn’t test to see whether the calculated amount of fuel input actually resulted in effective combustion. It has no feedback mechanism and is thus called an Open Loop Operation. Most modern engines solve this by placing an Oxygen Sensor (Also called an O2 sensor or Lambda sensor) in the header pipe of an exhaust system. It provides data that tells the ECU whether the mixture was lean or rich, and the fuel map is altered to compensate for it. Systems like this- that have a feedback mechanism- are called a Closed Loop Operation. If you’ve understood all of the above, you might have the most logical question- ‘If the oxygen sensor provides data on whether the mixture is lean or rich, why do we need all the aforementioned sensors?’. Good question. Unfortunately, with current technology, there is still a signal feedback delay between the sensor and ECU (it isn’t instantaneous like the other sensors), and is only truly effective when a constant throttle position is held, and not under constantly changing throttle inputs. Thus, it only serves as an add-on. But remember this point as it is important.

The Booster Plug

Ok, that’s all you need to know. Most relevant to the Booster Plug is the Air Intake Temperature and the Closed Loop system. In essence, the Booster Plug seeks to trick the Air Intake Temperature part of the equation into making the ECU think it is 20 degrees Celsius lower that the actual temperature. Why 20 degrees? Because every fuel injection ECU will enrichen the fuel mixture by 3% for every 10 degree drop in temperature, thus a 20 degree drop results in a mixture that is 6% richer than normal. This percent is constant for all modern vehicles because it depends on the density of air molecules and uses the same fuel, which is constant for all vehicles. Why only 6%, you ask? Well, let’s start with why a rich mixture in the first place. You see, richer fuel mixtures make an engine run smoother and results in a more linear throttle response. But go too rich, and you lose those advantages. 6% is the sweet spot.

Installing the Booster Plug is as easy as plugging in two connectors. If you can’t manage that on your own, perhaps you shouldn’t ride at all. The temperature sensor hangs off a cable that is to be placed in front of your air intake, and the connectors hijack the input signal, completing the symbiotic connection. But wait, what about that lambda sensor, you ask? Once it detects that the mixture is running rich, shouldn’t it tell the ECU to make it leaner, and then wouldn’t that undo everything? Well, yes, it would. But remember how the lambda sensor has a signal delay, and how it only functions best at constant throttle (told you that’s important)? That works to our advantage. At constant throttle (cruising), the ECU detects the richer mix and does indeed make it lean, which doesn’t matter because the advantages of a rich mix (smooth linear throttle response) are only felt when you increase or decrease throttle input. In fact, a lean mix at cruising actually saves you some fuel. And as soon as you apply throttle, the Booster Plug signal is back in play and you get a richer mix, again. Oh yeah, as for why motorcycle manufacturers aren’t doing this themselves from the get go, well that’s not their fault. The folks who make the bikes are more than capable of doing this and more, but they have been proverbially castrated by emissions regulations resulting in most modern vehicles being tuned to run a little leaner than usual, and this is felt most in the lower revs. It robs a bike of its low end rideability and some power, but it keeps emissions in check. And it results in slightly better fuel economy. Does the Booster Plug make it worse? Not really. Overall, I’ve noticed less than a 10% drop in fuel economy.

Honestly, the Booster Plug works as advertised. One thing to note though, is that it ensures a 6% fuel mix increase only in the temperature range of -23 to +37 degrees Celsius. Above that, it climbs to about 8%, but that’s probably not a temperature range you should be riding at anyway. For now, my Street Twin doesn’t feel like an unwieldy mistake, anymore, and it is far smoother than I remember. Is it a replacement for a taking a bike with a full system exhaust and a new cam to a professional motorcycle tuner who can design a map on a dyno? Probably not. But in the absence of said professional, it does an absolutely fantastic job, and for the price, it’s hard to find anything else that works as effectively as this. I’m stoked with it, and it’s going to be an essential upgrade for all my future motorcycles.

About the Author – Aadil Naik

Aadil holds a Masters in Business, and spent a few months in the corporate world before a chance encounter resulted in him replacing formal pants with leathers. He spent the better part of the last four years as a features writer for Motoring World, and even though he’s driven a couple of Lamborghinis, maintains that two wheels are the right number of wheels for an automobile. He spends all his free time (and money) trying to convince himself that his 2016 Triumph Street Twin is an ADV bike, and is constantly on the hunt for a good burger joint.