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Ships within 48 hours · Estimated delivery Oct 1 - Oct 6
For Your Every Summer RSVP, with Code: SUMMER15
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:
- 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
4.8 ★★★★★
Based on 9 reviews
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Product Reviews
★★★★★ 5
Snagged a deal
Size: 7, Color: Redwood/Gum 10
I waited and waited to get these boots! I knew I was chancing it, but they went on sale, and I snagged them! I am a size 7, and they fit nicely with socks. a little loose, barefooted, but what psycho wears boots without socks? They are comfortable and really well-made.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on April 8, 2026
★★★★★ 4
Cute, comfortable waterproof boots (a little snug to put on)
Size: 7, Color: Velvet Tan/Gum 2
These are really cute Chelsea-style boots and feel very comfortable once they’re on. The waterproof material is great for wet weather and the sole feels sturdy with good traction. They look stylish enough to wear casually but still feel practical for rainy days.
The only downside is they can be a little difficult to put on at first because the opening is somewhat snug, but once they’re on they fit well and feel supportive. Overall they’re a great waterproof boot and I’ve enjoyed wearing them.
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Reviewed in the United States on March 17, 2026
★★★★★ 5
Surprisingly great for my wide feet and high instep!
Size: 10.5, Color: Velvet Tan/Gum 2
So thrilled I took a chance on these. Finding boots is impossible for me. I have wide feet, a super high instep, a bunion on one foot, and I wear a hard to find size (10.5). I ordered the 10.5 and 11 in these expecting I might need to size up for width (if I could even get them on). It was a struggle getting the 10.5s on the first time, and once I did they were somewhat uncomfortable on the top of my left foot. But I read that they would relax so decided to give it a go because I need waterproof boots for an upcoming trip and the 11s felt too long. After two days of light wear, they are already breaking in and I have no more discomfort. Getting them on is already easier and they are plenty wide enough and very comfortable to walk in. These are true to size. Super happy and worth a day of mild discomfort to break them in!
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Reviewed in the United States on March 7, 2026
★★★★★ 5
Comfortable, sturdy, waterproof
Size: 9.5, Color: Black/Black
Loce, love, love these boots. Have walked ten miles with no foot pain around NYC. They go with everything and and are so comfortable. As they are waterproof/resistant, they get a little warm in high temps, but perfect three-season boots.
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Reviewed in the United States on May 17, 2026
★★★★★ 5
Super cute, comfortable, practical, love that they are slip on
Size: 10.5, Color: Tobacco/Black
I have worn these 2-3 times already. The first day was a school/work day so I was on my feet 9 hours and the only issue I had was with the side of the boot rubbing against my ankle. I just make sure I wear socks high enough to cover my ankles or jeans that go into the boots now for long wear days.
Absolutely love them! They keep my feet dry in this snow( we live in Michigan). I had been looking for a pair like this for awhile now and was getting super frustrated that I couldn't find my size in any that I liked. I saw that they had these available in a 10.5 and I wear 11. I looked at the Sorel website reviews (since the amazon ones weren't super helpful on sizing) and they said that the boots ran big so I took a chance on the 10.5 fitting me. They fit perfect. I have long narrow feet but I could see where they would be tight or uncomfortable on someone with wider feet. I've been trying to find a pair for my mom now since she has boot envy.
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Reviewed in the United States on January 27, 2026
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