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Exhaust› Headers, Manifolds and Components

Doug Thorley

4:1 Headers w/ Y-Pipes, 1-3/4" Primary, 2-1/2" Collector

$1,540.00 $1,530.00 Save $10.00

SKU: THY-340-C

Out of Stock
Special Order
Ships in 4–6 weeks
Free Shipping over $200
$100 Minimum Order
30 Days Return
INSTALL DIFFICULTY
DIY PRO SHOP

Moderate — 2–4 hours

Overview

The Doug Thorley THY-340-C is a set of V8 headers designed for performance enhancement. Constructed from 14-gauge steel tubing with 3/8-inch thick flanges, these headers are coated ceramic inside and out for durability and heat resistance.
Show original supplier description
The Doug Thorley THY-340-C headers and Y-pipes are engineered to enhance the performance of select V8 models. Specifically designed for the 5.3L V8 engine found in the 2006-2009 Chevrolet Impala SS, 2005-2009 Chevrolet Monte Carlo SS, 2005-2008 Pontiac Grand Prix GXP, and 2007-2009 Buick Lacrosse, these headers aim to extract more power. Constructed from robust 14-gauge steel, these headers feature a 4:1 design with 1-3/4" primary tubes and a 2-1/2" collector. They are finished with a silver ceramic coating, which helps to reduce under-hood temperatures and provides environmental protection. The kit includes bolts, and the Y-pipe has a 2-1/2" inlet that connects to a 3" outlet, requiring welding for installation. The product is 100% American-made and includes a limited lifetime warranty. Installation notes specify that the Y-pipe outlet must be welded to the exhaust inlet. Crucially, these headers are NOT legal for street use on pollution-controlled vehicles and CANNOT be shipped to California due to emissions regulations.
Vehicle Symptoms
  • Loss of engine power at high RPM
  • Check engine light on after exhaust work
  • Poor fuel economy during acceleration
  • Rough idle or hesitation
  • Exhaust smell inside cabin
Relevant Conversations
  • V8 headers vs stock manifold power gain
  • Doug Thorley THY-340-C installation guide
  • Best headers for my V8 truck
  • Symptoms of restricted exhaust on V8
  • How to improve V8 exhaust flow
  • Headers causing check engine light fix
  • Ceramic coated headers vs stainless steel
  • V8 headers installation time and difficulty
  • Doug Thorley headers review forum
  • Exhaust upgrade for more horsepower

Product descriptions are provided by our supplier partners and may not always be perfectly accurate. Not sure this fits? or call (760) 282-4645 and we’ll verify before you order.

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Specifications

BrandDoug Thorley
Part NumberTHY-340-C
CategoryExhaust
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Built for enthusiasts. Every order is backed by our 30 day return window on eligible items. Unused and uninstalled products may be returned with approved RMA and no restocking fees when received in new condition. Orders placed through the MOTORMIA app with a complete build qualify for our Fitment Guarantee — free return shipping if the part doesn’t fit your exact setup. The guarantee covers fit only; installation must follow manufacturer instructions, and we recommend a qualified shop for parts marked Difficulty 4–5.

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Shipping

Orders are processed in 1–3 business days. In stock parts ship promptly from our partner network. Special-order items either aren’t currently stocked or are built to your spec — expect 4–6 weeks. If a part goes on backorder while your order is in the queue, we’ll reach out and work through discounted alternatives together.

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