SKU: 77262188315

Holley HP EFI ECU and Harness Kits 550-604N

Sale price$1349.97 Regular price$1499.97
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USA
  • USA
  • CAN

Ships within 48 hours · Estimated delivery Aug 6 - Aug 11

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Description

Holley HP EFI ECU and Harness Kits 550-604NHP ECU AND HARNESS, MPFI, NTK Looking for a plug and play alternative for your stock or built late model factory EFI engine? How about a replacement ECU for your older Holley C950? Holley has you covered. HP EFI ECU and harness kits are designed to be used with popular factory EFI engines as an alternative to the factory ECU and harness or as a replacement for your C950 ECU. The HP allows you to accurately control the fuel and ignition of your engine

HP ECU AND HARNESS, MPFI, NTK
 
Looking for a plug and play alternative for your stock or built late model factory EFI engine? How about a replacement ECU for your older Holley C950? Holley has you covered. HP EFI ECU and harness kits are designed to be used with popular factory EFI engines as an alternative to the factory ECU and harness or as a replacement for your C950 ECU. The HP allows you to accurately control the fuel and ignition of your engine along with additional controls for nitrous, boost or water meth.

Features:

  • Optional 5.7” full-color touchscreen LCD allows easy on-the-fly tuning, data-logging or can be used as an easy to see graphical gauge panel
  • Eight sequentially driven 8:2 peak and hold injector drivers, capable of driving up to 16 low or high impedance injectors as a standard feature. Multiple staged injector strategies
  • Eight channel Distributorless Ignition (DIS)outputs capable of directly driving “Smart” ignition coils or Holley DIS coils. Will drive 2 wire coils with the addition of PN 554-112 high current coil driver module
  • Integrated single channel wide band oxygen sensor control. Works with NTK or Bosch sensors
  • Internal data-logging standard with a huge 2GB of memory
  • 4 Stage progressive nitrous control
  • Turbo boost control
  • Integrated water/methanol injection control
  • Self-tuning fuel table strategy greatly simplifies tuning process
  • Individual cylinder fuel and spark control allows you to unlock your engine’s potential
  • Works with 4, 6, 8 cylinder engines
  • Unique lb/hr based fueling strategy greatly simplifies and commonizes tuning
  • Advanced idle, closed loop, and enrichment strategies allow for very stable operation
  • ECU is fully potted and can be mounted in the engine compartment or interior
  • Sealed automotive and marine grade connectors
  • Allows for use of common OEM sensors as well as customer sensor calibration input
  • Ignition Plug and Play with GM HEI, Ford TFI, magnetic and hall effect trigger, and other ignition systems. New Plug and Play applications in process. Custom settings can be configured to allow many other applications
  • 1-5 Bar MAP sensor capability
  • Two channel knock control sensor Inputs for both one or two wire knock sensors
  • Dedicated fuel and oil pressure inputs
  • Controls both stepper and PWM Idle Air Control (IAC) motors
  • Speed density, Alpha-N, or combination fueling strategies
  • 4 Programmable high or low Pulse Width Modulated (PWM) outputs and 4 fully configurable inputs can be configured for use
  • 4 Stage nitrous oxide control
  • Fully featured nitrous control eliminates the need for a separate nitrous controller device
  • Can be configured “Wet” or “Dry” with closed loop feedback
  • Progressive control based on time, RPM, or boost, requires part # 554-111
  • Lean or rich safety cutoff
  • Full timing retard/control configurability per stage based on RPM or time
  • Integrated Water/Methanol injection control
  • Uses Holley Water/Meth solenoids specially designed and calibrated for use with this EFI system to allow the user to enter Water/Meth flow as a percentage of fuel injector flow for Water/Meth tuning precision unmatched in the industry

Application

  • Universal

Specs

Brand Holley EFI
Emission Code 3
Ignition Type Coil - (No Timing Control)
  Ford TFI
  GM HEI Small Cap
  Holley Dual Sync Distributor
Injector Connector Jetronic / Minitimer (Bosch)
Product Type HP EFI Kit
Part Number 550-604N
Shipping Notes
  • Free Standard Shipping on $100+ Orders to the USA.
  • Except Preorder products are shipped in 48 hours.
  • Delivery to the USA:
  1. Standard Shipping : 3-10 business days
  • If time is of the essence, please consider selecting expedited delivery for faster service.
Exchange/Return Notes
  • We offer a 30-day return/exchange service after receiving.
  • Final sale items are not eligible for returns or exchanges.
  • To process your return/exchange, please contact us at [email protected]
  • Please click here for more details>>> Return & Exchange Policy
SKU: 77262188315

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Cora Jane
Lexington, US
★★★★★ 3
Not long lasting for a chewer!
Size: Medium
These are massive! I have a golden retriever puppy and she chewed through the yellow ring very quickly. They keys are much more durable.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on March 25, 2026
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Pudgy
Houston, US
★★★★★ 5
Size small. Perfect for little guys
Size: X-Small
These are my pups favorite chewy. He’s 4 months 5lbs. I was having issues with chew toys being too big. I got the small. They are perfect!
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Reviewed in the United States on April 7, 2026
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Jennifer L Johnson
New York, US
★★★★★ 5
Great for puppies- have purchased several times
Size: X-Small
I have purchased this toy for a couple of the puppies in my life and they always love it. It’s not noisy, it’s made for puppies to chew (so it’s not too hard), and it’s fun for them to carry around with the different keys and key ring. A little pricey, but it always lasts a very long time- longer than they are a puppy!
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Reviewed in the United States on June 15, 2025
E
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Everyday Essentials Reviewer
Port Orchard, US
★★★★★ 5
Safe and Entertaining Chew Toy
Size: Medium
My dog absolutely loves this toy! She gets hours of chewing time out of it, and I feel so much better knowing the keys are made of a material that’s gentle on her teeth. Unlike harder toys that can chip teeth, this one is durable yet safe, and it keeps her happily entertained. Definitely a great choice for any dog that loves to chew.
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Reviewed in the United States on August 20, 2025
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Milarah
Belleville, US
★★★★★ 5
Best money spent on a safe puppy chew toy
Size: X-Small, Size: X-Small
One of the best chew toys you can buy for your puppy! This kept him occupied for quite a while and it is one of his favorites.
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Reviewed in the United States on April 24, 2026

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