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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:
- 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 990 reviews
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Product Reviews
★★★★★ 4
Good enough
Color: Black
Comfortable chair. Easy to put together. Allen nuts aren't cut perfectly so sometimes hard to get the wrench in there. My biggest complaint, and I didn't even realize this until I sat down in it, the arm rests are not adjustable and they are a little short for my liking.
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Reviewed in the United States on March 17, 2026
★★★★★ 5
COMFY CHAIR GOOD SUPPORT
Color: Dark Brown
So I needed an office chair because the one that I had wasn't really helping my back any. And it just didn't have enough cushion on the chair because when you want to sit for hours at your desk you want to be comfortable. So I took a chance on buying this chair. I thought the color was good and the price was right but I was still a little nervous because it said put together. So I got it right away only took 3 days. And the directions for pretty easy there were a couple of spots that I think we're out of order because you had to kind of play around with the screws going into the holes from the arms but I think if I were to get another chair like this I would probably do it my way because it's pretty self-explanatory but I followed the directions that came with the chair. And hey I'm 65 years old and I put this chair together. It's nice it's sleek and oh my God is it comfortable!!! Right where my lower back and sciatic is I get the support and it just feels good and I know that if I have to be at my desk for 3 or 4 hours I'm going to be comfortable. I highly highly recommend getting this chair.
The only issue that I had was the driver did not leave it on my porch. I had ordered a Vizio TV a couple months ago and the driver brought it up to my porch. So I just had to go out and take two steps bring it into the house I really appreciated that.
This driver didn't even come through the gate and there is no signs of any dogs because there aren't any. So this driver just left this giant heavy box it was about 35 lb in front of the garage where it was very visible from the road. And I had a dragon to my front door it was heavy I did not like that at all. But it wasn't damaged or anything and I do love the chair. I just don't like what the driver did.
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Reviewed in the United States on November 3, 2025
★★★★★ 5
Great sturdy chair and beautiful color
Color: White
I love this chair. I bought it for my home office. It is beautiful, sturdy and very comfortable. I'm not good at all with assembling even basic things but I would say that this was relatively pretty simple for someone like me to put together. Good price and good product.
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Reviewed in the United States on April 3, 2026
★★★★★ 4
Reliable, Comfortable, and Good-Looking Chair — I Keep Coming Back to It
Color: White
This is my fourth time purchasing this Amazon Basics mid-back office chair, which says a lot about its overall value. It looks clean and modern, fits well in a home office, and is genuinely comfortable for daily use. I typically get about a year and a half out of each one, which feels reasonable given the price point and materials.
Out of the box, the chair is easy to assemble and immediately comfortable. The padding is supportive, the armrests are well positioned, and the faux leather gives it a more upscale appearance than many chairs in this category. It rolls smoothly, swivels easily, and works well for long computer sessions without causing back or shoulder fatigue.
That said, this is not a lifetime chair. After extended use, the cushioning and structure do begin to wear, and that’s usually when I replace it. Still, considering the comfort, appearance, and cost, it remains one of the best value office chairs I’ve found — which is why I keep buying it again.
Pros:
• Comfortable padding and good mid-back support
• Clean, modern appearance that looks great in an office
• Smooth rolling and stable base
• Easy assembly
• Excellent value for the price
Cons:
• Durability is moderate; expect replacement after about 1½ years
• Not designed for long-term heavy-duty use
Verdict:
If you want a comfortable, attractive, and affordable office chair that performs well for daily use, this is a strong choice. It may not last forever, but its comfort and value make it easy to recommend — and easy to repurchase.
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Reviewed in the United States on January 18, 2026
★★★★★ 5
Highly recommend
Color: Black
Very sturdy, the cushions make it super comfortable. The size and ease of movement are perfect. Assembly was super easy. A very quiet chair. Wonderful all around value.
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Reviewed in the United States on February 28, 2026