last updated 18/12/2017
A sprint booster, also called wind booster, pedal box, idrive, throttle controller, pivot controller, electronic throttle controller, e-drive, plug n go module, pedal commander or throttle re-mapper, is a device that intercepts the signal between the accelerator pedal and the engine management on a fly by wire throttle. It takes the signal from the pedal and outputs a modified signal to the engine management. Claimed benefits include faster engine response, elimination of throttle delay, better performance and the ability to unleash the true potential of the engine. How do they work and do they really enhance performance?
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 control
- 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.
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.
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.
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.
Installing a sprint booster means the available travel in the accelerator pedal is not fully utilized. There is a large dead zone where the voltage sent to the engine management is 100%. This means you’ve lost precision in throttle control. You’ve lost resolution. Your ability to make small adjustments to throttle has been degraded. You can’t feather the throttle.
Using more throttle and having a more jerky driving style will cost you more fuel, wear out your car more and increase your chances of having an accident. It also encourages poor driving habits – for example accelerating hard then braking hard in stop / start traffic rather than just driving at a steady speed.
Offroad, a sprint booster makes it difficult to control your vehicle. Movement of your foot caused by vibration or bumps translates to much larger accidental changes to throttle then what would occur with a standard setup. Your ability to make small changes to throttle is compromised, yielding an amateur like driving style over rough terrain. Many sprint booster users will de-activate their sprint booster when offroading. Actually some vehicles automatically do the exact opposite of a sprint booster when low range is engaged in order to improve precise vehicle control. The disadvantages of sprint boosters whilst offroading are also present when on the road, but the effect is more pronounced offroad due to the rough terrain and the requirement to precisely control speed and torque whilst offroad.
A sprint booster cannot circumvent the filtering performed in the ECU. Whether people describe a sprint booster as a “proportional controller” or talk about “digital setpoints” or “controller gain” or “ramp up” or “tuning” is irrelevant.
The accelerator pedal transducer is a potentiometer with a voltage across it. It is not an intelligent device. There are no time delays or filtering performed within the accelerator pedal transducer. The filtering is done in the ECU. Why? Why would the vehicle manufacturer add complexity, expense and points of failure within the accelerator pedal transducer when that capability is already there in the ECU? Add a few lines of code and it’s done in the ECU without any extra hardware, cost or potential points of failure. Also, filtering removes information. You want to remove information only at the point where there is no disadvantage to removing it. In the case of the throttle position, the sensor usually consists of two potentiometers which both report directly to the ECU. This means the ECU is able to detect problems which could pose a safety risk. High frequency noise, step changes in signal or transient discrepancies between the two signals can be used to rapidly detect problems. Filtering at the throttle transducer would mask these issues. Diagnostic ability would be lost. Instead, the raw data is read from the device and interpreted and manipulated as required using software within the ECU. The raw voltage signals from the transducer go to the ECU where diagnostics are be performed. After that the signal is filtered and processed within the throttle controller.
So filtering occurs within the ECU, not within the accelerator pedal transducer. This means it’s physically impossible for a sprint booster to circumvent the ECU filtering. The filtering is occurring within the ECU, after the sprint booster. The sprint booster is not changing the ECU’s software.
What does the ECU filtering do and how does it impact the performance of a sprint booster? Engine management may filter the incoming voltage signal to make the throttle control smoother. It’s called a low pass filter. Fast changes are filtered out. High frequencies are filtered out. This manifests as a maximum rate of change that the throttle can respond to. So even if the voltage signal from the accelerator pedal instantaneously jumps from 0 to 100%, the actual throttle will be limited in how fast it can react so that it takes some minimum amount of time to open fully. As an example, lets pick a value – say 0.2 seconds. This means that no matter how quickly you change the voltage signal, if you change it at a rate faster than the rate equivalent to 0 to 100% in 0.2 seconds, it makes no difference to the actual throttle response. So engine management filtering actually masks the response of a sprint booster. Some people argue that the sprint booster will help overcome the engine management filtering. This is impossible. The filtering is occurring after the sprint booster. The engine management does not know whether the voltage signal is coming from a sprint booster or directly from the accelerator pedal. It will always limit the rate of change in throttle the same way. It is incorrect to suggest that the engine management’s filtering somehow enhances the response from a sprint booster. It will always dampen the response. So the time saving of 0.1s from having to move your foot less will actually result in less than 0.1s improvement to throttle opening time. Part of the increase in speed from the sprint booster is filtered out. Faster signals get filtered more. If you are already at the limit without the sprint booster then adding a sprint booster will make no difference at all. So, for example, if you can already move the accelerator pedal from 0 to 100% in 0.2s which corresponds to the maximum rate of the throttle filter, then adding a sprint booster and reducing the time it takes for the accelerator position to reach 100% by 0.1s will have absolutely no impact to the actual throttle opening time. The filter is already saturated before adding the sprint booster.
When it comes to pros and cons of a sprint booster it largely comes down to user preferences and opinion. In my opinion sprint boosters don’t offer any benefits, provided you have adequate articulation of your foot and leg. People perceive improved response with a sprint booster but, if they desired that response without the sprint booster, all they had to do is operate the accelerator pedal aggressively. It is simply a voltage amplifier and you can only ever have between 0 and 100% throttle regardless of how you amplify it. The response provided by a sprint booster can be perfectly replicated by pushing the accelerator pedal further, minus the almost imperceivable time it takes to move the pedal a bit more. A sprint booster adjusts the voltage signal that indicates accelerator pedal position. It’s extremely clear that the scope of a sprint booster’s control is limited to adjusting the apparent position of the accelerator pedal. Some sprint booster owners will argue the response can’t be emulated by pushing the pedal harder and faster. Most certainly it can. The system is very simple to evaluate. The laws of physics are extremely clear. The manufacturer themselves confirm it in their technical data. There is no claim to be made to the contrary unless the physics can be explained.
So in my opinion there is no advantage. Why be forced to be jerky with the throttle when you could have a choice? Why throw money at yet another electronic gizmo when it may not be necessary? The perceived advantages are not really there, but the disadvantages are real. I prefer having precision control over the vehicle’s throttle. I prefer driving smoothly, efficiently and safely. And I prefer spending less money on gizmos and more money on things that make me happy like getting out in nature and camping.
That doesn’t mean you shouldn’t get a sprint booster. Many people like them. In fact I’d suggest that most people who’ve tried one like the result. People like the feel of the throttle response. Regardless of the fact that they can be perfectly replicated by pushing the pedal further, if you enjoy driving with a sprint booster then it’s a good thing. Try one out and see if you like it. However it is not a performance enhancement and won’t improve engine response or acceleration.
Possible Safety Issue
I doubt sprint booster manufacturers have performed detailed analysis of the accelerator pedal position transducer failure modes and how the ECU software detects and handles those failures. Therefore it’s possible that a sprint booster could mask a problem with the accelerator pedal and leave you with a stuck throttle without the ECU noticing. Similarly the sprint booster itself could fail and result in a stuck throttle. The risk is low, I’ve never heard of it happening, but it could happen.
It’s very hard to find any good experiments on sprint boosters. There’s simply far too many uncontrolled variables to make a valid experiment and the effect of confirmation bias and placebo is too strong. People are eager to validate their investment and will usually confirm everything the marketing has trained them to believe. This is not unique to sprint boosters, it happens with all consumer spending. As an indicator for how strongly people want to confirm, consider these two points:
- Some sprint booster vendors / manufacturers clearly state that a sprint booster will not improve 0 to 100km/h acceleration times.
- Some sprint booster users claim that a sprint booster does improve 0 to 100km/h acceleration times.
Consumers are inventing their own advantages to validate their spending, even though it is contrary to the manufacturer. Similarly sprint booster users believe a sprint booster can somehow circumvent ECU throttle processing despite the sprint booster’s only interface to the ECU being the accelerator pedal position.
There is one experiment that is really good. It measures directly parameters from the ECU. It eliminates nearly all the uncontrolled variables. It confirms everything in this article. Everyone interested in sprint boosters should read it. Check it out here:
Even some sprint booster manufacturers validate what I’ve stated in this article. Most use vague and ambiguous language but some are more honest. Here is one example: