SKU: 44499070246

Holley HP EFI ECU & Harness Kit (HO550-601)

Sale price$2636.55 Regular price$2929.50
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Description

Holley HP EFI ECU & Harness Kit (HO550-601)HO550 601 HP EFI ECU WITH HARNESS Suit GM TPI & Holley Stealth Ram Part Number: HO550 601 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

HO550-601 - HP EFI ECU WITH HARNESS

Suit GM TPI & Holley Stealth Ram

Part Number: HO550-601

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.
NEW V2 SOFTWARE FEATURES:
"Quick Start" ignition and fueling strategy for LS x Engines
Data Logger. Scalable axes, Smoothing, Multiple graph view ability, Pre-defined notes fields and many more
Strip Chart Real-Time Data Viewer
Integrated Boost Control - Boost vs Time, Boost vs Gear (Time or RPM), Boost vs RPM, Boost vs Speed, Launch control. Boost launch builder, Over-boost safeties, Boost scramble
Traction Control - Power reduction via timing, nitrous percentage or boost (Requires Davis Technologies Holley Module)
“Quick Start” fueling for all engines
Option for VE based fueling strategy
Fuel Map and Learn Function Smoothing
Configurable User Password Protection
Fully Configurable lap top Gauge Panel
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
Plug and Play control of factory GM 24x and 58x LSx engines
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 24x and 58x LSx engines, 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/Meth

Shipping Notes
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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]
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SKU: 44499070246

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4.3 ★★★★★
Based on 26 reviews
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Verified Purchase
Liz Newman
Lexington, US
★★★★★ 5
Comfortable and cool. Does not ride up.
Color: 01-multicolour (4-pack), Size: Medium
Extremely comfortable. Stays cool. Ample coverage. Quality material. They do not creep up. I ordered a medium which I generally take a size small. I have reordered and will reorder again to add more colors to my collection.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on May 18, 2026
J
Verified Purchase
Janola
Bozeman, US
★★★★★ 5
Great Value for Cool Thigh Protection
Color: 02-multicolour (4-pack), Size: XX-Large
For the price, I'm not sure there are better women's boxer shortlettes anywhere. I've tried more expensive brands, and for quality and cooling, these are right up there. I have other bamboo viscose undies that still get gross when I get sweaty in the summer, but these, with the large mesh panel, really help wick away a lot of that moisture, keeping you feeling dryer and cooler. I find that the leg openings are comfortable and don't roll up! and the waist band doesn't dig, nor does it roll down. These do not provide any compression, and I wasn't looking for any. I just wanted some cooling, thigh protecting women's boxers that wouldn't break the bank. These are them! Bonus- I've washed them and put them in the dryer (following their instructions), and they haven't shrunk; they look about the same and are nice and soft.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on July 28, 2025
R
Verified Purchase
Reviewer
Waukegan, US
★★★★★ 4
Great for the entire family but expensive
So far so good. The brand of boxers we had been buying changed their style and construction so we needed to find an alternative. These have held up well so far to multiple weeks of frequent washing and wearing from the entire family. We did size up from the usual 6/M we normally buy and ordered large to prevent the legs from rolling up which worked out great. Our daughter likes the length and how soft the fabric is for wearing under skirts and gym shorts and liners stay put without moving or leaking as another reviewer mentioned. Our son says they are comfortable and fit well being just supportive enough without being constrictive. We all agree that there seems to be not enough fabric in the back as they tend to be much tighter across the backside than the front and that also causes the waist band to ride lower in the back than the front. These have better seam placement than some brands we tried with no seam across the lady bits and no seam down the middle of the back side so they are more much comfortable but the cost is also much higher and that is why we're only giving it 4 stars. These will stay in the rotation until we find something cheaper that both us and the kids like.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on January 24, 2026
B
Verified Purchase
Brittany
Lake Worth, US
★★★★★ 5
Pregnant lady review! Soft, comfortable, cool.
Color: 03-multicolour (4-pack), Size: Large
So soft, comfortable and cool. I'm pregnant and I've gained weight in my legs. I love wearing dresses but my thighs were rubbing together too much. These are perfect to wear under dresses. I also wear them under my bibs at work and it keeps me from getting overheated but I don't have to worry about whether or not my underwear show since they just look like shorts. I wish these came in maternity. I just keep them below my belly. I'll be buying more for sure.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on April 8, 2026
J
Verified Purchase
Janessa L.
Louisville, US
★★★★★ 5
I want to live in these
Color: 01-multicolour (4-pack), Size: Medium
I bought 4 different sets of new underwear. Unfortunately these came last. It’s unfortunate, because if they had come first I would have cancelled all my other orders or returned them and ordered more of these. I never want to wear anything else ever again; these are the comfiest undies I’ve ever owned, I want to live in them. I can wear them under pretty much anything except leggings or very tight pants (but let’s be honest, I don’t wear those anyway.) They are incredibly soft and breathable, they wash well, don’t roll, keep my thighs from rubbing, are comfy to sleep in, and the colors were true to the photo. Just a heads up, they are on the thin side and just a bit see through in the rear. I’m 5’5” 140lbs and the mediums fit perfectly, they go about mid-thigh.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on July 30, 2025

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