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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 |
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4.5 ★★★★★
Based on 20 reviews
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Product Reviews
★★★★★ 5
6 Star Immersive Read
Format: Audiobook
5 Stars (+1 with the audio for 6 stars) immersive read.
Synopsis:
After a brush with death and the loss of her father, Silla Nordvig has fled to the Road of Bones. A perilous journey north to safety and freedom. But the Road of Bones is a dangerous place filled with man, monster, and monsters who are men alike. After a second encounter that should have killed her, Silla decided to hide in a wagon bound North. A wagon owned by the notorious Bloodaxe Crew, a band of mercenaries on their own mission. Will she make it to Kopa in the North, to freedom and safety, or will she be hunted down by what travels the Road of Bones with her?
Review:
This is an INCREDIBLE read. The book is amazing and the audio made it legendary. All hail Islay Jacobs, a single narrator that put on a full cast performance!
A fantastic Viking based Romantasy set in a world where magic users, Geldra, are despised, warriors fight monsters for honor and coin, and few are truly safe. An epic adventure, sizzling romance, hidden secrets, corrupted power (with quotas), unparalleled world building, found family, and not enough books out yet!
There are so many good twists in this story, some caught me completely off guard which is impressive. I am normally quick with plot points and while I did pick up on several, a few had my jaw on the floor. Each character was richly crafted, the story driven by their strengths, needs, desires, fears, and flaws. I can see why so much of the world has been drawn to this story. I’m late to the party, but I can’t wait to continue in this world.
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Reviewed in the United States on March 27, 2026
★★★★★ 5
Road of Bones was just what I needed!!!
Format: Kindle
⭐️⭐️⭐️⭐️.5 from me! The Road of Bones
Silla Nordvig is running for her life from the Queen’s assassin and the King’s Claws (The Klaernar) but she doesn’t know why. She and her father were attacked by warriors on the road to home where he was killed, he admitted he wasn’t her true father, but that’s about all he could say before he died in her arms. Now, Silla has joined the Bloodaxe Crew, trying to make her way north on the Road of Bones to safety.
The Road of Bones by Demi Winters is a Romantasy for those who absolutely love some romance with their fantasy. It’s Vikings and warriors at their finest. I felt the book was a little bit of a slow start, although there WAS action from the first chapter. But as soon as Silla realized she had to run for her life, the action was non stop. The plot was so well done, the story just built upon itself, and we learned more and more about Silla as her memories returned and her assassin got closer. As we discovered more about Silla, we learned more about the Bloodaxe Crew. Both Silla and the Bloodaxe Crew (each member) have such great back stories.
Silla is such a well fleshed out character. We see her as a simple kitchen maid who has little self-esteem, but longs for the freedom to be herself, and we grow with her into a woman that knows herself and is ready for just about anything. She goes through so much on her journey on the Road of Bones and we are there with her for every minute. We get to see her fall in love, and we see her when she goes through betrayal. The way she reacts internally shows just how much she grew throughout her journey.
The supporting characters, Jonas, Ilias, Hekla, and Rey were all extremely important to Silla’s story in his or her own way, and made the book all that much more rich and layered. Jonas seemed to have become enthralled with Silla, but things happen there that cause serious trauma. Hekla is a great friend to Silla and watching that relationship flourish was simply a joy, and Silla was able to come into her own as a warrior through Hekla’s tutelage (with Rey’s help). And, Rey, we can never forget about Rey…he was terrifying to Silla in the beginning, but somewhere he turns into a pillar of strength for her and I, for one, cannot wait to see what happens with that relationship.
In the end, I consider Road of Bones to be a work of art. If you are looking for a Viking Romantasy that is fun, a little dark, and absolutely heartbreaking, this should be your next read.
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Reviewed in the United States on February 12, 2026
★★★★★ 3
I'm done
Format: Kindle
I survived. I made it through the book!
This is a very slow book. Like... incredibly slow. I get that it's world building, but there also needs to be a sense that this world is worth caring about.
The good side is that the author has lovely writing. And the audio book reader is fantastic. But the story itself is paced incredibly slowly and without the depth needed to care about the characters or world. I fell asleep a few times with the beautiful reader and lovely words... telling a story I just wasn't interested in
The downside is that Silla is one of the most annoying main characters. She is weak and naive, with essentially no backstory. She's traveled all over with her father but apparently cooking and bread are her only skills. No worldliness. No experience with men or, well friends at all.
Yet on the flip side she's able to learn fighting skills in a few weeks and starts outright flirting quite detailed within a few days. So is she a naive weak maiden or a hidden temptress warrior? No idea. Not sure she knows either.
The other character backstories are also quite shallow. Like a few lines were written and that's all that needs to be said.
But...it is lovely writing.
I bought the 2nd book at the same time that I bought the first. I honestly have no desire to read the 2nd but curiosity has me wondering if it actually gets to storytelling.
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Reviewed in the United States on March 13, 2025
★★★★★ 4
Wolves in disguise, magic, and political intrigue!
Format: Audiobook
📖 The Road of Bones by Demi Winters
Rating: ⭐⭐⭐¾ (3.75/5)
This book had me at "let them think us lambs, when truly, we are wolves." The Road of Bones delivers on atmosphere and world-building, though I was initially drawn in by promises of fantasy romance with a strong female lead. What I got instead was a first book that's laying serious groundwork - heavy on political intrigue and lighter on the romance than I expected.
Silla Nordvig's journey along the thousand-mile Road of Bones is genuinely compelling. Fleeing after her father's murder with the queen's assassins on her tail, she's constantly testing her limits. The Viking-inspired setting feels fresh, and the magic system stands out as something I haven't seen before. When the Wolf tells her, "Careful, Sunshine. The sharp part bites," I couldn't help but smile at their developing dynamic.
The pacing occasionally stumbles, but the character development keeps things moving. Silla's transformation from hunted to hunter unfolds beautifully against the backdrop of political machinations. The emotional moments hit hard, especially as she discovers her own strength in a world determined to break her.
For a first book in a series, it establishes a solid foundation, though I wish the romance elements weren't quite so slow-burn. If you're looking for immediate romantic payoff, you might be disappointed, but if you enjoy watching characters and worlds unfold with patience, you'll find plenty to love here.
📦 What to Expect
✨ Epic Fantasy
💖 Slow Burn Romance
🔥 Grumpy/Sunshine Dynamic
🤯 Complex Politics & Power Struggles
💔 Deep Emotional Growth
🦴 Magical Beasts or Sentient Magic
⚔️ A Lead Who Fights for More Than Survival
📚 Book Tags
Keywords: Dark Fantasy, Magic, Romance, Political Intrigue, Found Family, Survival, War
Tropes: Grumpy/Sunshine, Enemies to Reluctant Allies, Found Family, Mentor/Protegé, Slow Burn, Power Couple
Triggers: Slavery, Violence, War Themes, Grooming (discussed), Sexual Assault (mentioned, not shown), Emotional Abuse, PTSD
🎯 Final Thoughts
If you're in it for the long haul and appreciate a fantasy that takes its time building something meaningful, The Road of Bones is worth the journey. Just know you're signing up for a series that's just beginning to show its teeth.
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Reviewed in the United States on November 8, 2025
★★★★★ 5
Good start to a series
Format: Kindle
I delayed reading the series for reasons I don’t remember. But my TBR list is huge so I thought I’d take a shot of this and I was pleasantly surprised. I didn’t think the blurb about it was anything special. But it was a very good book. It took some interesting twists and turns. I am so glad the second book is already out. Because I would not have waited patiently. Very slow burn but good storyline. 🔥🔥/5
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Reviewed in the United States on January 3, 2025