SKU: 5270546285

Holley HP EFI ECU and Harness Kits 550-604

Sale price$1237.47 Regular price$1374.97
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  • CAN

Ships within 48 hours · Estimated delivery Jul 16 - Jul 21

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Description

Holley HP EFI ECU and Harness Kits 550-604MPFI HP ECU AND HARNESS KIT 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

MPFI HP ECU AND HARNESS KIT

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 550-604
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: 5270546285

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4.9 ★★★★★
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Coffee and Cats
Draper, US
★★★★★ 5
Love the fit!
Love the fit and feel of this tank. Feels casual yet classic. I wish it came in more color/print options. A red stripe or a green stripe would awesome! I am 5'1" and 165 (large chest) and a large fit perfect!
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Reviewed in the United States on May 1, 2026
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Rawrr
Battle Creek, US
★★★★★ 3
Love the print, but didn't like the style...
Size: Small, Color: Dark Camel Leopard
I'm 5'5 114lbs 34B and got the "camel" leopard print in size small. I think it's technically a cute shirt and it fits okay, I guess, but the style and color ended up looking terrible on me! For reference, the size small measures 21 inches long (from the center of the front collar to the bottom), and about 18 inches wide. I find the style really unflattering on me. The color seemed like it would be flattering for most skin tones, but it ended up making my yellowish skin tone (I'm half asian) look sickly. Also note that this shirt is made of rayon, which is sensitive to heat, so if you get it (and you like it) you should keep it out of hot water and avoid putting it in the dryer if you don't want it to shrink. As for the fit, I usually wear size small unless I want my shirt to fit oversized or flowy etc, so I got this in small. It fits loose enough to be comfortable, but this type of collar is so unflattering on me (I could deal if it was either higher or lower) and the curved hem and in-between length just doesn't suit my body type. LOL, apparently, the fact that it has a cool print still doesn't change the fact that the "muscle" tee style looks terrible on me. It might suit someone else though. The fabric is stretchy and soft, but it's not clingy or see thru (might be in other colors though). The armholes also don't gape at all (doesn't show any of my bra). I ended up having to return it.
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Reviewed in the United States on June 23, 2022
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Trizian Lacson - Canoza
Massapequa, US
★★★★★ 5
Comfy
Very comfortable clothes and it fits me just quite right.
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Reviewed in the United States on June 11, 2026
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Meagan Hendrix
Fort Morgan, US
★★★★★ 5
Perfect Summer Tank!
Size: X-Large, Color: Black
I recently added the Amazon Essentials Relaxed Fit Sleeveless T-Shirt to my everyday wardrobe, and I’ve been pleasantly surprised by how versatile and comfortable it is. Fit & Comfort: True to its name, the relaxed fit is roomy without looking baggy. It’s ideal for casual wear, working out, or layering under jackets and cardigans. The sleeveless cut offers great freedom of movement, and the armholes are well-designed—not too tight and not too loose. It’s flattering on different body types and long enough to cover the waistband comfortably. Fabric Quality: The cotton blend is soft, breathable, and holds up well in the wash. It’s not too thin or see-through, which I appreciate. It also doesn’t cling, making it perfect for hot days or light workouts. Style & Versatility: The design is simple but stylish—easy to pair with leggings, shorts, or jeans. Available in multiple colors, so it’s easy to stock up for mix-and-match options. Price Point: Great value for the price. It's budget-friendly without feeling cheap, and it performs just as well as more expensive basics from other brands. Minor Cons: Some lighter colors may show sweat slightly more. If you prefer a more fitted look, you may want to size down. Final Verdict: The Amazon Essentials Relaxed Fit Sleeveless T-Shirt is a solid everyday staple—comfortable, affordable, and stylish in a low-key way. Whether you're lounging, running errands, or hitting the gym, this tee gets the job done.
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Reviewed in the United States on June 12, 2025
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Rebecca Madureira
Draper, US
★★★★★ 5
Nice
Size: Large, Color: Forest Green
These are really nice very soft and a great value for the price! Runs true to size Only issue for me would be the armpits are a bit large. But the colors are beautiful also
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Reviewed in the United States on March 4, 2026

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