MHD map slots and flash options
Four map slots, a cruise-stalk switch, and thirty-plus flash-time options. How MHD's slot system works — and which settings actually deserve your attention.
A tune used to mean one map burned into one chip. MHD's slot system is the modern version: up to four calibrations living on the DME at once, switched from the driver's seat in seconds, plus a stack of options you set once at flash time. Here's how the pieces fit.
How slots work
- Up to **4 switchable map slots** per flash — either MHD's OTS MultiMap selection or a custom multi-map tune from your tuner.
- Each slot carries its own fuel/octane selection, and OTS maps add a **power level slider** (60–100% in 5% steps) — valet and low-boost duty lives here.
- Switching is in-car, engine running: hold the cruise **TIP** button (E-chassis) or **SET/LIM / BC** (F/G-chassis) for ~2 seconds. The tach needle points at the active slot, the CEL blinks, the rocker chooses, and the selection survives key-off.
- **Reflashing resets to slot 1.** After any flash, expect slot 1 regardless of what was active before.
- The active slot is a loggable channel — "Current Map" — so your datalogs always know which calibration they came from.
Picking an OTS map is a three-way decision: stage (which assumes a hardware level — our stage guide explains the honesty there), fuel (91/93/95 octane, or ethanol blends where the fuel system allows), and transmission (torque scaling).
What each write type changes
| Write | When | Scale |
|---|---|---|
| Full Write | First install, full uninstall | The long one — charger on |
| Long Write | Adding/removing options that carry MHD+ code (flex fuel, map switching) | Most of the map, still slow |
| Map Write | Stage or fuel change between flashes | Seconds to a couple of minutes |
| Slot switch | Any drive, any time | Instant, no flashing at all |
The design intent: options that need custom DME code force a Long Write; everything routine should be a Map Write or a stalk sequence. If you find yourself full-writing often, something's misplanned.
The flash-time options that matter
MHD documents thirty-plus options; these are the ones our customers actually ask about:
- **Burble / exhaust crackle** — adjust how aggressive, or skip it. Your neighbors vote.
- **Cold-start delete** — kills the cold-start rpm flare. Legal-for-you considerations aside, it exists.
- **Vmax delete** — removes the speed limiter.
- **Boost per gear / torque per gear** — the traction lever on high-power cars; see the WGDC guide for how we use it.
- **T-MAP sensor (3.5/4 bar)** — must match the physical sensor you installed. Mismatch = garbage load calculations.
- **HPFP / coil / injector support options** — required flags when the matching hardware is fitted.
- **Wastegate rattle fix** — changes commanded gate position at idle/decel; it addresses the sound, not worn bushings.
- **OEM catted downpipe** — stops the CEL suppression so emissions readiness monitors can complete. The fix for "my monitors won't set."
- **Flash counter reset/freeze** — see the flashing guide's honesty note; an option, not an invisibility cloak.
OTS maps versus custom tunes
OTS ("off-the-shelf") maps are the shared shelf: solid, conservative calibrations built for declared hardware. They're the right first flash and a great control group. A custom tune — ours, or anyone's — starts from your stock file, your hardware list, and your fuel, and refines against your datalogs through the revision loop. The slot system doesn't care: OTS MultiMap and custom multi-map tunes both fill the four slots.
One flex-fuel wrinkle worth flagging here: with MHD's true flex setup, all four slots must be pump-gas map selections — the ethanol blending is done live by MHD's code from the ethanol reading, not by picking an E85 slot. The flex-fuel sensor guide covers the wiring; this is just the slot-side rule.
Sources
- Map switching and slots: [MHD map-switch documentation](https://mhd-tuning.atlassian.net/wiki/spaces/MFS2/pages/11763743)
- Flash options catalog: [MHD flash options](https://mhd-tuning.atlassian.net/wiki/spaces/MFS2/pages/10813500)
How do I switch maps without reflashing?
With the engine running, hold the cruise TIP button (E-series) or the SET/LIM or BC button (F/G-series) for about two seconds. The tach becomes a slot indicator, the CEL blinks, and the rocker selects. A full reflash always resets the car to slot 1.
What is Stage 0 in MHD?
A stock-power calibration with MHD still installed. You keep enhanced logging and flash options while the engine behaves like factory — the right setting for a dealer visit or a clean baseline log.