Tunes are often at the forefront of discussions when it comes to increasing horsepower. This is especially true with the number of forced induction engines on the market. BMW shifted nearly their entire lineup to turbo engines in the past decade. Fortunately, for us performance enthusiasts, turbo engines generally leave tons of power on the table. Tunes alone are capable of adding 50-100+ horsepower on otherwise stock engines. However, there is a lot that goes into choosing the right tune for your goals.
Before reading the rest of this post you're likely asking, "Which tune gives more power?" Obviously, most car enthusiasts are likely tuning for additional power. We'll touch on horsepower gains throughout this post. However, we wanted to lay the groundwork early. For the purpose of this post we're mostly focusing on the following BMW engines:
The above list of BMW engines are the modern turbo engines with excellent tuning potential. These engines have tons of options on the market and it would be impossible to cover every engine and tune in one post. As such, we will reference the following tunes throughout:
- JB4 Piggyback Tune
- MHD Flash Tunes
- bm3 (bootmod3) Flash Tunes
Of course, the basic concept behind flash and piggyback tunes remain regardless of the engine or specific tune in question. We will simply reference examples using the above tunes to make this post relevant to BMW.
BMW Piggyback Tunes (JB4)
If you've read some of our other content you likely know we love the JB4 piggyback tune. It's the primary piggyback tune on the market for turbo BMW's. A few other piggyback options have come and gone, however Burger Motorsports JB4 has been around since the early N54 days. Again, the concepts of piggyback tunes remain. We've simply chosen to reference the JB4 due to its excellent success on turbo BMW's.
How BMW Piggyback Tunes Work
A piggyback tune is similar to a "chip" tune in that it plugs directly into the ECU (also known as the DME). It does NOT re-write the factory ECU tune, though. Rather, piggyback tunes alter certain signals and sensors to accomplish the tunes goal. Essentially, the factory DME tune remains unchanged, and the piggyback tune is "tricking" the DME into making more power. It may trick the DME into running more aggressive ignition timing, increasing boost, etc. This depends on each specific tune in question.
For example, the JB4 acts as an advanced boost controller. It simply alters the boost target of the DME, but the DME never actually sees the increase in boost. In other words, the DME thinks it's completely stock. As a further example, the N54 runs about 8psi stock boost. You then install the JB4 tune which targets, let's say, 14psi. The turbos are indeed running on 14 pounds of boost, but the DME still sees 8psi.
You may be thinking, "Wait, we've got a problem here." Right? We don't want to get too technical here, but there is somewhat of an issue. The DME thinks it's running 8psi, but it's truly running 14psi. The piggyback tune isn't altering any fueling or timing tables in this case. However, more boost generally requires less ignition advance and additional fuel flow. You're going to run seriously lean if the engine is taking in more air without additional fueling.
However, this isn't the case. A JB4 does not cause lean conditions despite the fact it's calling for additional airflow without the supported fueling adjustments. Why? Modern BMW DME's are incredible. They process an astounding amount of data in milliseconds. As such, the DME immediately recognizes the need for additional fuel, less ignition timing, etc.
Pros of Piggyback Tunes
- DME remains stock
- Advanced safety features
- Easy & safe installation
- On the fly map changes
The first two piggyback tune pros go hand in hand. The DME remains stock and still believes it's running within stock parameters. Therefore, if uninstalled prior to a dealer visit they will be unable to detect that the car was tuned. Additionally, the stock DME safety features remain untouched. Piggyback tunes, like the JB4, typically build in additional safety features too. For example, if the JB4 detects dangerously lean AFR's it will revert back to stock boost in milliseconds. Next, they are incredibly easy and safe to install. Piggyback tunes are generally considered "plug and play" tuning solutions. Simply connect the tuning box to the ECU and have fun. No chance of "bricking" the DME; more on this in the flash tunes section.
Finally, since piggyback tunes do not re-flash or re-write the ECU they allow on the fly map changes in seconds. The JB4 can go from stock, to a modest daily driving tune, to kill mode in a matter of seconds. Piggyback tunes are further loaded with unique features. The JB4 offers gauge hijacking, steering wheel controls, and meth injection support among many other awesome features.
Cons of Piggyback Tunes
- Limited to capabilities of stock DME
- Less precise
Circling back to the basics of piggyback tunes - they do not re-write the DME. As such, the piggyback is limited by the factory tuning parameters. At some point, the factory DME will flow as much fuel as it is possibly programmed to. You can keep cranking up boost with the piggyback tune but now the engine will start leaning out since the ECU maxed out its fuel flow. Long story short, piggyback tunes have their limits. However, this likely only matters for those looking to make crazy horsepower figured. All of the above mentioned BMW engines (N54, N55, B58, N63 etc) will nearly max out the stock turbos capabilities before the factory DME capabilities. The JB4 only truly becomes limiting when absolutely maxing stock turbos or opting for aftermarket turbos.
However, there is another downside even on modestly tuned and modified engines. Piggyback tunes are not as precise overall. Yes, the JB4 is one of, if not, the most advanced boost controllers available (even more precise than most flash tunes). Though, it is less precise than flash tunes when it comes to fueling, ignition timing, etc. A piggyback tune relies on the factory ECU to make the adjustments. As such, you cannot precisely control them through tuning.
BMW Flash Tunes
Bootmod3 and MHD tunes are two of the most popular flash tuning solutions for BMW engines. Both offer off-the-shelf map selections along with the ability to opt for custom flash tunes. We'll reference these tunes throughout this next section to keep it relevant to BMW. However, the concept of flash tunes remains the same regardless.
How BMW Flash Tunes Work
Flash tunes are also similar to "chip" tunes, but in a different way from piggybacks. Like chips, flash tunes actually re-program the DME. However, they are uploaded to the DME rather than being physically plugged into anything. Flash tunes are generated on computers and the software is then loaded to the cars computer, the DME, generally through the OBDII port.
Since flash tunes are just software, you can essentially do anything with a flash tune. You can create your own fueling, timing, and VANOS tables, just to name a few. The options are endless and flash tunes can be tweaked and customized to create the perfect tune for your BMW. Unlike piggyback tunes, the DME sees the exact data from the tune. When the turbos are running 14psi, the DME sees that 14psi.
Pros of Flash Tunes
- Unlimited capabilities
- CAN be safer than piggyback tunes
As discussed briefly above, a big pro of flash tunes is the customization ability. You can make minor tweaks to fueling, if needed. Or, you can completely change every tuning parameter. This allows for better precision than piggyback tunes. Tying into that, there are unlimited capabilities with flash tunes. You are not limited by the stock DME's parameters. Of course, you are limited by the engines hardware and that should be respected. More on this in the below cons section.
Finally, flash tunes CAN be a safer option than piggyback. You can opt for a flash tune that plays it safe and run conservative ignition timing. Further, you can opt to run a bit on the richer side to avoid lean conditions and engine knocks. Again, the idea behind flash tunes is that everything can be customized and perfected for your exact goals.
Cons of Flash Tunes
- Alters DME
- Chance of "bricking" DME
- CAN be riskier than piggyback tunes
Flash tunes actually re-program the DME. Even if you flash back to the stock DME tune a dealer will still be able to tell the car was modded if they go digging. Running any tune under warranty, including piggyback tunes, should be at your own risk. However, a dealer is more likely to recognize a flash tune. Further, there is a chance of "bricking" your DME upon loading the flash tune. This is unlikely when done correctly. Even if you do "brick" your DME it can often be reversed and fixed. However, it may require some advanced software or a visit to the repair shop.
Furthermore, flash tunes can be a lot riskier than piggyback tunes. Don't be fooled by tuners posting nearly unbelievable horsepower numbers. The horsepower numbers may be legit. However, they may be building tunes that are pushing the ragged edge. If not done right, flash tunes may potentially run ignition timing that is too aggressive. BMW's have excellent knock sensors and the DME is quick to react. However, riding the knock sensors is never a good idea.
*Another con: most off-the-shelf flash tunes cannot be customized. They are programmed by the tuner and locked for editing. Customized flash tunes are really the best all around option (if done by a knowledgeable, reputable tuner) but come at additional costs.
Flash vs Piggyback Tunes: Horsepower & Performance
Alright, the part everyone has been waiting for. Let's just get it out of the way now. There should be minimal horsepower differences between piggyback and flash tunes, assuming all else equal. However, there is a lot more to it. Again, tying back into the potential risk of flash tunes, a flash tune may make more power than a piggyback tune if you're pushing the ragged edge. By adjusting timing on a flash tune you can force the DME to target very aggressive timing and ride the knock sensors. The stock DME with the piggyback simply will not allow that to happen. In this case, the flash tune with more aggressive timing will likely make a bit more power. On the contrary, you may opt for a conservative flash tune that targets less aggressive timing than the piggyback.
Sometimes horsepower gains from tuning are a balance of risk and reward. You can be riskier and push the ragged edge for extra power, or play it safe for a bit less power. Piggyback tunes generally fall somewhere in the middle. Flash tunes fall where ever you and/or your tuner decide. Of course, piggyback tunes can also be safe or aggressive. It depends which tuner you get the piggyback tuner from. Also, with the JB4, you can opt for lower maps with low boost targets or more aggressive maps that push stock turbos to the limits.
Finally, as we discussed in the piggyback section these tunes do have their limits. At some point a flash tune will be required to push further. Again, most of the turbo BMW engines can nearly max out stock turbos on piggyback tunes with proper bolt-ons and fueling. This mostly becomes an issue on upgraded turbo and heavily modded BMW's. However, even on stock turbo BMW's, piggyback tunes will reach their limits on heavy E85 mixtures. The stock DME with a piggyback simply cannot flow the required fuel. However, most of the record holding and highest horsepower modern turbo BMW engines run piggyback tunes.
All of this leads us back to what we truly believe is the best tuning solution.
Ultimate Tuning Solution: Piggyback + Back-end Flash Tunes
That's right. You can actually combine a piggyback tune with a flash tune, typically referred to as a back-end flash. Combine the pros of both tunes and eliminate some of the negatives. We run JB4's with MHD back-end flash maps on our N54's. It is a setup we highly recommend to others. A few pros of the JB4 + back-end flash combination include:
- Advanced safety features
- JB4 retains its superior boost control
- Flash tune retains its precision and customization
- Unlimited tuning capabilities
- Tune as safe or aggressive as you want
- JB4 retains on-the-fly map changes
There are tons of pros to stacking piggyback and flash tunes. Piggyback tunes, such as the JB4, retain their advanced safety features, superior boost control, on-the-fly map changes, steering wheel controls, etc. The flash tune then takes control of fueling, timing, VANOS, and load tables, to name a few. This brings in the additional precision and customization that piggyback tunes alone cannot provide.
We want to touch a bit more on the on-the-fly map changes. Depending on the specific BMW engine, the JB4 has about 7 built-in maps for various boost targets. Remember, the JB4 is still in control of boost here. You can change that map in seconds on the steering wheel. The flash tune remains unchanged, and you can go from stock, to a daily driver tune, to absolute kill mode in seconds. The only way to change these boost targets with ONLY a flash tune would be to re-flash the car. That means having the cables and software (tune) ready to go and still having to pull over, turn off the ignition, wait for several minutes while the new tune loads, etc.
Why the Highest HP Turbo BMW's Still Run JB4's
This ties into some of the pros above. However, the JB4 has superior usability for supporting mods to make crazy power numbers. Port injection can be integrated directly with the JB4; alternate methods are required if you're only running a flash tune. The same can be said for integrating E85 sensors with the JB4. The JB4 has better meth control features, too.
The point is, piggyback tunes can do things flash tunes alone simply cannot do. Likewise, flash tunes do things that piggybacks cannot. Combine the two for the best of both worlds. Whether you're shooting for 1000whp or a modest 500whp stock turbo BMW, it's tough to go wrong with a piggyback and back-end flash stacked.
Flash vs Piggyback Tunes: Summary
Modern DME's, especially BMW DME's, process astounding amounts of data in seconds. This allows for unique tuning solution such as piggyback tunes. They "trick" the DME into making more horsepower and allow it make the necessary adjustments. Flash tunes re-program the DME and allow for precise, customized tuning. Both flash tunes and piggyback tunes have a handful of their own pros and cons. All else equal, they will make similar power numbers. In our opinion, you cannot go wrong opting for either a piggyback or flash tune.
However, piggyback and flash tunes can actually be combined for the best of both worlds. This is truly the ultimate tuning solution, in our opinion. Piggyback tunes retain their superior integration and usability features while flash tunes provide precision and customization. Nearly all modern turbo BMW's pushing the envelop of horsepower are running JB4 piggyback tunes coupled with back-end flashes.