REAPER·CONTROLS

Products/Fuel Pump Control/Grim Max

3D render of the Grim Max prototype enclosure with the Reaper Controls logo and a mounting ear, shown with its pre-rename lettering 3D RENDER · PROTOTYPE ENCLOSURE · PRE-RENAME LETTERING

REAPER CONTROLS

Grim Max Closed-Loop Fuel Pump Controller

Dual-Pump Fuel Controller, Drives Up to Two Golems, Closed-Loop PID Pressure Control, Tach Input, Bluetooth Setup, Potted Enclosure

Prototype Hardware Not yet for sale. Prototypes in bench testing.

EXPECTED PRICE $299

Control method
Closed-loop PID on measured fuel pressure
Pump outputs
2, individually enabled
Power switching
One Golem per pump output
Fuel systems
Carbureted and EFI
Included
Harness, pressure sensor, mounting screws
Tach input
12V square wave, Holley / Haltech / ACES
Setup
Veil app over Bluetooth (iOS and Android)
Get Notified Full Specifications

Specifications

BrandReaper Controls
Product lineGrim Max
Part typeClosed-loop fuel pump controller
Control
Control methodClosed-loop PID on measured fuel pressure
FeedforwardRPM-based, corrected by pressure feedback
Pressure feedbackFuel pressure sensor, included
Pressure targetsCarbureted and EFI ranges, set in the app
PrimingTimed prime on key-on
Engine-stop shutoffPump shuts off when the engine stops, the way a factory system does
Stopped engine vs. lost signalCharging voltage is used to tell the two apart
Loss of tach signalKeeps the pump running on pressure-only control
Outputs
Pump outputs2, individually enabled
Output typePWM control signal to a Golem power module
Pump current capacitySet by the Golem driving it (40A each)
Dual pump operationUser-configurable staging; auxiliary pump exercised periodically
Inputs
Tach input12V square wave; reads Holley, Haltech and ACES tach outputs directly
Sensor connectorKeyed connector, harness included
Setup & app
ConfigurationVeil app, Bluetooth (iOS and Android)
Setup methodGuided wizard: fuel system type, then RPM source
Live dataFuel pressure and duty cycle in the app
Settings storageOn the module; no phone needed to run
Fault handlingDegrades gracefully and reports to the app
Electrical & physical
System voltage12V automotive
PowerIgnition-switched
ProtectionResettable fuse, transient suppression, reverse polarity
EnclosurePotted, mounting ears both sides
Designed inMissouri, USA

Features

  • It measures pressure, it doesn't guessFuel pressure is read continuously and the duty cycle is corrected to hold your target, whatever the engine is doing. Most aftermarket PWM control is a fixed duty cycle or an RPM threshold wearing a nicer label.
  • Two pumps, one controllerRun a single pump or two. Each output is enabled on its own, with your rules for how a second pump stages in, and the auxiliary pump is run periodically so it isn't sitting unused for a season.
  • Carbureted or EFIThe same controller holds a steady 6 to 7 PSI for a carburetor or an EFI target, set in the app.
  • Reads your EFI's tach outputHolley, Haltech and ACES 12V square-wave tach outputs wire straight in. No adapter needed on the common conversions.
  • Shuts the pump off when the engine stopsKey on and it primes; stop the engine and the pump shuts off, the way a factory system does. Grim Max checks charging voltage to tell a stopped engine from a dropped tach signal, so a flaky signal doesn't shut your pump down mid-drive — it keeps running on pressure-only control instead.
  • Set up from your phoneA guided wizard in the Veil app walks through fuel system type and RPM source. Settings live on the module.
Rear three-quarter view of a classic Mustang fastback, taillight and quarter panel in low evening light

About Grim Max

Most PWM fuel pump control in the aftermarket is a binary switch dressed up as something smarter: a fixed duty cycle, or a duty cycle tied to one RPM threshold. It isn't watching pressure at all. It's watching RPM and guessing.

Grim Max is built around a real closed loop. Pressure is measured continuously and the pump's duty cycle is adjusted to hold the target, whether that's a steady 6 to 7 PSI for a carburetor or an EFI pressure. RPM still plays a part as feedforward, but pressure is what drives the correction. That's the difference between a controller that responds to load and one that approximates it.

Grim Max owns the pressure logic and hands the power switching to Golem, so each piece does the job it's actually good at. Prototype boards are in hand and in testing.

In English and Scandinavian folklore, the church grim is the guardian of a churchyard, said to be the spirit of the first creature buried there, most often a black dog, set to watch over the ground. People who glimpsed it took it for an omen of death. It was standing watch the whole time. Grim Max does the same for your fuel system: it watches pressure constantly and acts before a problem ever reaches you.
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