This article is not a product review. I have not used a sprint booster. This article is purely analysis based on the following:
- information provided by sprint booster manufactures
- understanding of how throttle by wire works
- understanding of general process controll
- an excellent experiment that you will see in the references section below
Anecdotal evidence from people who have tried sprint boosters does not invalidate this article. This article is consistent with technical information provided by sprint booster manufacturers. I’m certain that the manufacturers themselves understand how their own product works.
Compromise
As with all after market accessories, it’s good to start from a skeptical position. Every design is a compromise. Usually after market accessories simply shift from one compromise to another. Offering some benefit almost always results in some negative effect. There’s no free lunch. We can safely assume that a sprint booster must have some negative impact. So before deciding on throwing your money at a sprint booster (or anything else), you should first identify what those negative effects are, to see if the overall response matches what you’re actually trying to achieve.
What does the Sprint Booster do to the Throttle Signal?
A fly by wire throttle is simply a voltage signal. The voltage tracks the position of the accelerator pedal via the accelerator pedal transducer. Pushing the pedal harder yields a higher voltage. The engine management system measures the voltage and thus knows the position of the accelerator pedal. A typical arrangement is shown in the schematic below.
A sprint booster sits between the accelerator pedal position transducer and accelerator pedal position input as depicted in the schematic below.
The only interface a sprint booster has to the ECU is via the accelerator pedal position input. So clearly the only thing that the sprint booster can influence is the accelerator pedal position that the ECU receives.
The sprint booster increases the rate of change of voltage vs pedal position. So for a given increase in pedal position, the sprint booster yields a larger increase in voltage compared to when stock. It fools the engine management into thinking you are pushing the pedal further. This is depicted in the chart below showing pedal position vs voltage.
The graph above illustrates the voltage signal that the engine management receives as a function of accelerator pedal position for both with and without a sprint booster. You can verify these graphs by looking at the documentation provided by sprint booster vendors. Actual sprint booster voltage profiles will not perfectly match the example I’ve provided. The exact shape of the curve doesn’t matter, the sprint booster is compressing more voltage change into less pedal travel.
So when stock, half pushing the pedal will yield half voltage. But in the example above with the sprint booster installed, half pedal will yield full voltage and the engine management will interpret the pedal position as being 100%. Pedal position between 50% to 100% is redundant – pushing the pedal more than 50% makes no difference and the useful pedal range is reduced.
There’s a few important conclusions based on this analysis alone:
- A sprint booster can manipulate only the accelerator pedal position. Nothing else.
- Accelerator position can only ever be between 0 and 100%, with or without a sprint booster.
- Without the sprint booster, any accelerator position between 0 to 100% can still be attained according to the actual position of the pedal.
- The perceived engine response delivered by a sprint booster can be completely emulated by appropriate positioning of the accelerator pedal.
Claimed benefits
Sprint booster vendors claim that the product eliminates throttle delay by cranking up the voltage or somehow making this signal “stronger”. This is not true. Any changes in voltage propagate from the accelerator pedal transducer to the engine management at close to the speed of light. This is the case with or without a sprint booster. The delay is so small it’s immeasurable. The sprint booster makes no difference to how quickly the engine management receives and interpreters the signal from the accelerator pedal. The engine does not respond faster. It cannot respond faster. The only difference is the engine management thinks the pedal is being pushed further than what it really is.
Some people are extremely satisfied with their sprint booster, reporting something like “the engine response was so good I smoked the wheels pulling out of my driveway.” But what has really happened here? The driver has accelerated harder than he or she wanted to. Essentially the driver has lost control of the vehicle. The vehicle has done something the driver did not want to occur. This is not a benefit. Actually it’s a disadvantage. Without the sprint booster, the driver could have still smoked the wheels by pushing the accelerator pedal harder. With the sprint booster, the driver has lost precision in throttle control. Throttle control becomes jerky rather than smooth. In fact compressing the range of throttle voltage into a reduced amount of pedal travel means the throttle control is approaching a more on / off type arrangement.
Some people explain that, when they turn off their sprint booster, the car feels extremely sluggish. Over time they have learned to adjust their foot control for the overly sensitive accelerator pedal response. It will take time for them to re-learn how to drive with the sprint booster turned off.
Another claimed benefit I’ve heard reported is that sprint boosters improve fuel economy because you aren’t pushing the throttle as hard to achieve the same speed. This is completely ridiculous. People that make such stupid claims shouldn’t be allowed to post on internet forums. They make people dumber. The reduced amount that you push the accelerator is perfectly offset by the amount that the sprint booster amplifies the voltage. Further, precision control is lost and driving style becomes more jerky, which increases speed variability, increases fuel consumption and increases wear on the vehicle.
Actual Benefits
The benefit of a sprint booster is that you do not have to push the accelerator pedal as far to achieve the acceleration you desire. You are saving some foot effort. There is no difference between installing a sprint booster to changing your driving style to operate the throttle in a more jerky fashion, for example flooring it violently when taking off. The only improvement in throttle response is the time it takes to push the accelerator pedal further. This is not reaction time of the driver. It is not the time it takes to decide to floor it. It’s the extra time required to move the pedal a bit more, given you are already moving it. I estimate for example it may take an extra 1/10 of a second or 100ms for the throttle to travel from 50% to 100% if you are already moving the throttle from 0% to 50%. So in a typical scenario where you want to accelerate hard, you’ll be better off by something in the order of 1/10 of a second with the sprint booster installed. Unless you accidentally break traction due to the reduced throttle precision, in which case you’ll be faster without the sprint booster. So if possibly saving 1/10 of a second is important to you, or saving the effort of moving your foot is important for you, then a sprint booster may be a good idea.
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