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For Your Every Summer RSVP, with Code: SUMMER15
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
4.7 ★★★★★
Based on 12 reviews
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Product Reviews
★★★★★ 5
So comfortable!
These work great and very comfortable. I put these on with heel moisturizer cream at bed time. Heels were improved overnight. They are washable too!
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on March 31, 2026
★★★★★ 3
Just aren’t large enough.
This is a great idea, and I can wear socks over them and not notice they are there. I just wish they came in a larger size. When I put cream around the edges of my heels where the cracks always are, I cannot stretch the socks wide enough to clear the heel without smearing the cream onto my fingers or on the sock cuff. They do stay in place and aren't squishy at all when walking. They smell good too. The price is right. I wore them overnight and my heels were indeed much softer and smoother than before, and felt moist (tacky) where the cream had been. So they do an amazing job, but after using them six nights, they just aren’t large enough for me to put on without a hassle.
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Reviewed in the United States on April 28, 2024
★★★★★ 5
these really work
saved my poor cracking heels
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on April 12, 2026
★★★★★ 5
Works for foot psoraisis
Size: 2 pairs black L
Got these for work (service industry) to reduce issues with psoriasis and blisters while putting on 20k+ steps a day. Over time the wounds healed and I could work without so much pain. I now don't use them all the time like I used to, only when a new lesion or blister appears, too prevent a breakout. Tip: if you're not in full breakout, wear thick socks under these as a barrier to friction.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on April 28, 2026
★★★★★ 4
Work well but run small
Size: 1 pair black L
They do seem to run a bit small. I bought them for my bf but snagged them from him because I couldn’t resist! I’m about a W8/12 and they were just a little big but unlike others, I just put them on while sleeping and didn’t walk around with them. If you’re just planning on that, they did a great job at sloughing and moisturizing 😎
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on April 25, 2026
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