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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:
- 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
4.6 ★★★★★
Based on 1700 reviews
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Product Reviews
★★★★★ 5
Impressive Power and Convenience Right Out of the Box
I just got this electric milk frother, and after only a few uses I’m already impressed. It has strong, consistent power that turns milk into smooth, velvety foam in seconds — perfect for lattes, cappuccinos, or even mixing matcha. The LED display is a surprisingly premium touch, making it easy to see and switch between speeds.
The fact that it’s rechargeable is a huge plus, and the 3‑in‑1 attachments give it more versatility than most handheld frothers. The charcoal black finish looks sleek and modern, and the build feels solid so far.
Even with just a handful of uses, it’s clear this frother delivers great performance and convenience. A fantastic little upgrade to any coffee routine — definitely a 5‑star start.
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Reviewed in the United States on May 22, 2026
★★★★★ 5
Reliable favorite kitchen tool
Color: Blue
This wonderful tool may be the most used tool in our kitchen. The hardest thing about it is to remember you can push the button and it runs- you don't have to hold it!. The charge on the rechargable battery last a long time- about 1 recharge per month- and we use it daily. We use the mixer attachment most. It works great for protein powders, collagen, iced tea or lemonade mix. It cleans easily and is waterproof- just make sure the cover is over the charging port. We have used it to froth milk, whip eggs, and as I said we use it daily to mix beverages. I worried about the price, but it is a great value because we bought it in December 2024 and it is more powerful and has already lasted longer than two whimpy ones.
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Reviewed in the United States on October 28, 2025
★★★★★ 5
Quality
Color: Black
This is by far the best frother I've used. Battery life is great. Its UX is excellent. Feels nice in the hand and has great power. Also like the on/off button as opposed to haveing to hold a switch down. Looking forward to getting their s3 scale.
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Reviewed in the United States on April 11, 2026
★★★★★ 4
Overall good frother
Color: Black
Bought the Maestri and the Zulay frother to test which one is better since both had good reviews. Returned the Zulay (see Zulay review) and kept the Maestri. Been using it for a few days now and works well. Mixes chai and hot chocolate well. It has one speed that is a good speed to mix, but not so fast that it causes the drink to spill over the top as long as the cup is filled to about 80% full. Because I tend to use the tall 20 oz Contigo autoseal cups, it could benefit from offering longer attachments to reach the bottom of the cup (note: that I did not find any company that offers longer attachment arms).
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Reviewed in the United States on January 28, 2026
★★★★★ 5
LOVE this frother and the creamy results!
Color: Black
I LOVE this gadget! And I'm not a gadget person.
Since I got it a few days ago, I've switched from using my Nespresso coffee maker, which uses pods and which I really like, to using Starbucks instant coffee packets (cheaper and more environmentally friendly than pods). I put a packet of the coffee and two packets of Equal in a cup, add half and half, then use this frother to mix them. Within a few seconds -- no more than 5, if that -- I have a thick mound of creamy froth. Then I had the water to finish making the coffee. Fantastic. This thing is so easy and fun to use.
This is not the cheapest frother available. I wanted a rechargeable unit that has sufficient power to make nice, creamy froth. Also, I didn't want to spend $10 and have the thing break and have to replace it. Reviews suggest the cheaper ones are fine if you don't regularly use a frother. I never used one before and didn't really think I would use it very often. But I like it so much, I've been using it twice a day.
Also, I first saw one in use while traveling in India. Another guest at my small hotel had one, which she used to make a latte with rather than drink the rather tepid offering at the more tea-oriented hotel. That's when I decided to get one. I'll be taking it on future trips. Some come with travel containers; this one didn't.
The only learning curve was making sure the cup or pitcher for the cream is deap enough not to splash out the cream. I think I'm actually using a little less cream than I used to because the volume increases so much. I use cold cream, not heated (I used to heat it in the microwave when I was using the NesPresso.) I find I like the initial contrast with the cold cream at the top, then I stir it down into the coffee. The Starbucks coffee is excellent. I've used it for iced lattes in the past, so I knew it was good. I can hardly wait for a heat wave to make them with this frother.
I did try to beater attachment in eggs when I was making an omelet. Not worth the trouble -- first, the bowl I was using to beat the eggs was too shallow and egg got all over. Second, a fork works just as well. If I were whipping cream, I would definitely use it.
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Reviewed in the United States on March 7, 2026