SKU: 63849965826

Adjustable Billet By-Pass Regulator-3/8 NPT - 12-879

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Description

Adjustable Billet By-Pass Regulator-3/8 NPT - 12-879Overview: Holley Billet Fuel Pressure Regulators are part of a complete line of fuel system products from Holley. They are precision machined from 6061 T6 billet aluminum for strength and durability. These regulators are adjustable from 4 65 psi and will handle both carbureted and EFI applications. A second pressure spring is included allowing you to increase the fuel pressure range up to 65 psi for EFI systems. They are offered with two port sizes, 3

Overview:

Holley Billet Fuel Pressure Regulators are part of a complete line of fuel system products from Holley. They are precision machined from 6061-T6 billet aluminum for strength and durability. These regulators are adjustable from 4-65 psi and will handle both carbureted and EFI applications. A second pressure spring is included allowing you to increase the fuel pressure range up to 65 psi for EFI systems. They are offered with two port sizes, 3/8" NPT or 6AN to adapt to your new or existing fuel lines. So, if you are currently running a carbureted system but plan to upgrade to EFI in the future, these regulators will have you covered either way.

Features:

  • Adjustable from 4-65 psi for precise fuel pressure adjustments
  • Constructed of billet aluminum with a black anodized base and a clear anodized top for good looks
  • Used in systems with a return line back to the tank
  • (1) 3/8” NPT Inlet; (1) 3/8” NPT Outlet; and (1) 3/8” NPT Return Port
  • Includes fitting for manifold reference
  • Includes an 1/8 NPT gauge port
  • Boost Reference - 1:1
  • The 4-15 psi carbureted spring comes installed in the regulator
  • Compatible with diesel fuel and E85

Application:

Year Make Model Submodel Engine Size
Universal

Specs:

Brand Holley
Color Black
Emission Code 5
Fuel System EFI/Carb
Fuel Type Gasoline
Inlet Size 3/8 inch NPT
Material Aluminum
Outlet Size 3/8 inch NPT
Product Type Fuel Pressure Regulator
Return Size 3/8 inch NPT
Style Bypass
Warranty Limited 90 Day
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SKU: 63849965826

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Jason Bolton
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★★★★★ 5
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Great book! It is helpful as I work towards my Masters of Science in Applied Artificial Intelligence
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Reviewed in the United States on December 20, 2025
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This is a solid book for understanding the art and science of working with LLMs and other generative AI models. I always struggled with getting the output I was looking for, and wasn't sure how best to "ask" the models for what I wanted. This book did a great job of laying out the strategies and practical guidance to craft the prompts. There were a lot of tips and tricks, but the overall understanding and framework around prompt engineering has been super useful.
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Reviewed in the United States on June 25, 2024
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Matt B
Waukegan, US
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A must read!
Format: Paperback
Hands down, the best book on prompt engineering and implementing LLMs. Really enjoyed Michael and James deep dive. Whether you're technical or not, this book is foundational to a deeper understanding in how to properly explore and implement LLMs.
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Reviewed in the United States on June 25, 2024
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SR
Battle Creek, US
★★★★★ 4
Helpful for GPT/LangChain framework
Format: Paperback
I applaud the authors for putting forth a comprehensive introduction in a rapidly evolving space. I absorbed a lot, helpful as I was developing a prototype — using open source methods. And that’s where I was disappointed. The LLM and examples are highly adapted to OpenAI’s GPT-x and the bulky LangChain framework, something not obvious until you dig in to the book. Sure, this may be where newbie demand was when the authors began writing. But as the open source models and OpenAI alternatives gain speed (e.g. Llama 3.1, Groq, etc.) this book may quickly need an updated and expanded version to stay relevant.
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Reviewed in the United States on August 7, 2024
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K. Wain
Pawtucket, US
★★★★★ 3
Good concepts, but uneven depth
Format: Paperback
Some helpful prompt frameworks, but parts felt repetitive and a few sections stayed too high-level for advanced users. Beginners will likely benefit more than experienced practitioners. If you’re new to prompt engineering it’s a decent starting point; if you’re already building structured prompts daily, it may feel light.
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Reviewed in the United States on January 17, 2026

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