The difference
A flash tune (APR, IE, REVO, N75, bootmod3) writes new software into the engine computer: boost, ignition timing, fuelling and limits. A plug-in box (RaceChip, DTE) or a piggyback (Burger's JB4) connects to the engine's wiring and changes the signals the factory computer works with, leaving its software as it is.
Five cars, side by side
| Car | Stock | Plug-in box | Flash tune |
|---|---|---|---|
| VW Golf GTI Mk6 | 200–210 PS | RaceChip GTS 5: +64 hp, €429 on sale | APR, IE: 245–275 hp, $366.95–$449 |
| Hyundai Elantra N | 276–286 hp | RaceChip +49 PS, DTE +56 hp, aFe +60 hp: $583.80–$697 | 295–350 whp, $499.95–$1,350 |
| Hyundai Kona N | 276–280 hp | RaceChip +50 PS, DTE +56 PS: €549–€689 | 295–330 whp, CAD 799.99 (N75) or $1,250 (LAP3) |
| Audi RS3 8Y | 401 hp | RaceChip +60 PS (€479–€609); JB4 up to +100 whp ($679) | APR 446 hp and up; $1,200 + $1,000 unlock |
| Mercedes-AMG A45 S | 421 hp | RaceChip 490 PS (€609); RENNtech module 490 hp | Weistec W.1: 510 hp, plus an unlock; tunes $1,499–$2,580 |
Each car links to its guide, where every claim and price links to the maker's page. Boxes usually quote a gain and flash tunes a total, so compare each with the stock figure. Elantra N and Kona N flash figures are at the wheels (whp).
When a plug-in box makes sense
- The car can't be flashed yet. For the 2024 Cupra Leon and Formentor facelift, RacingLine says the engine computer "cannot yet be tuned via the traditional methods", so plug-in modules are the option. The same goes for some Tiguan Mk3 and Octavia RS Mk4 engines.
- You don't want to unlock the computer. Flash tunes on the BMW M2 G87 need a bench unlock first; the JB4 piggyback doesn't. On the Genesis G70 the JB4 also works on a locked computer.
- You want to go back to stock easily. Modules from ABT, MTM, RaceChip and JB4 leave the RS3 8Y's factory computer untouched, and RENNtech's A45 S module has a bypass plug that returns the car to stock.
When a flash tune is better
- You want the most power for the money. On most of these cars the flash tune claims more power; on the Kona N our guide notes that plug-ins and the JB4 "add less".
- You plan Stage 2 and beyond. Stage 2 and 3 files are written for downpipes, intercoolers and bigger turbos; boxes stop at Stage 1.
- You want the gearbox tuned too. Gearbox software comes from the same flash tuners (see do you need a gearbox tune?).
Either way
Neither is invisible to the law or your insurer: both change the car's power. Check whether a box has a parts certificate where you live (DTE lists a TÜV Austria certificate for the TT RS 8J; RaceChip's Tiguan Mk3 box has no German parts approval), and tell your insurer. See is a tuned car legal and insured?
Keep reading
- How much does tuning cost?
- 95 or 98 octane after a tune
- MHD, bootmod3, Cobb or EcuTek? Which tuning software works on your car
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