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Jeep Headers for Wrangler and CJ


 Advantages of Thorley Jeep Headers

Jeep HeadersWhat are Tri-Y headers and how do they work?
We frequently get calls asking us to explain the theories behind the Tri-Y headers, but it just can't be done properly over the phone. To make things easier, this information will give you a basic idea of the key elements of Tri-Y design theory.

Why are headers so important?

It takes energy to push disorganized exhaust gases out through a vehicle's stock manifolds. Headers don't make horsepower they simply relieve the engine from the task of shoving exhaust out through stock manifolds. Installing properly designed headers frees up the energy previously wasted pushing out exhaust, and allows it to be used in propelling the vehicle. This increase in efficiency brought on by the installation of headers can be thought of as free horsepower.

Jeep HeadersWhat's the idea behind Tri-Y's?

It all begins with firing order. While you are shopping for a Jeep header... for familiarity's sake, we'll use the Chrysler / GM firing order on an 8cyl engine: 1, 8, 4, 3, 6, 5, 7, 2. Principle is the same. If you were to lay the cylinders out so that the first four cylinders in the firing order were on top of the second four, and then connect each cylinder on the upper row to its counterpart on the lower row, you'd have something that looks like the diagram to the right.

You've just connected, or paired, the cylinders that fire 180 distributor degrees apart from one another. Check this out on a distributor and you'll see that #1 is directly across from #6, #8 is directly across from #5, and so on. If you could pair your header tubes like this, you would have theoretically ideal headers. One pair of cylinders would fire every 180 degrees of distributor rotation. The high-pressure pulses from each paired set of tubes would be allowed one complete crankshaft revolution's worth of time to smooth out before its partner cylinder fired. The pulses would be organized so they could proceed out the tailpipe in an orderly fashion.

Jeep HeadersSo what does all this have to do with the Tri-Y design?
Let's go back to our first four over second four firing order stack and see how close we can get to pairing the cylinders 180 degrees apart without having to cross over or under the engine. Cylinders 1, 3, 5, and 7 are on the driver's side of the engine. Cylinders 2, 4, 6, and 8 are on the passenger's side of the engine. Let's do the driver's side first by referencing the diagram to the right.

Jeep HeadersIf we blend the gases from #1 with those from #5, and blend the gases from #3 with #7, we get the paired cylinders much closer to being 180 degrees opposite one another than if we just dumped all the exhaust gases together and let them fight their way out of the collector as a four-tube header does. Now check out the driver's side on the left.

That's all there is to it. Relatively simple, very effective and applicable to V6, straight 6 and 4cyl engines as well.

So why aren't all headers Tri-Y's?

Mainly because they're very labor intensive to manufacture and most companies are looking to produce a cheap header over a true performance header. This is also why Thorley takes the time to make every header they produce, 50-state SMOG legal. Each header comes with CARB certification papers and sticker. Very few headers on the market do this which makes their headers illegal in most places.

Why are most Doug Thorley designs Tri-Y's?

Doug Thorley Headers firmly believes that where possible, the Tri-Y design is the way to Make It Go! We hope this article eliminates some of the mystery surrounding the Tri-Y designs, why they build them, and why we sell them!

Header construction. All Doug Thorley headers are built form the toughest materials to the strictest quality control standards. 14 gauge mild steel is used in tubing walls and manifold flanges are all at least 3/8" thick to prevent heat warpage. All headers also come with a nickel-chrome finish. Your header will have a shiny chrome finish at installation and Thorley's rust protection ensures it will look like a million bucks longer than your vehicle's body will last.


jeep headersThe Doug Thorley Cat-Back Exhaust System juices-up your Jeep with free-flowing power. It utilizes custom CNC mandrel-bent 16-gauge aluminized steel tubing to eliminate restrictions and backpressure. The mandrel bending provides a full diameter tube thru all bend so there are no choke-points in the system... unline the factory exhaust which has a bunch of bend that squish the tube diameter way down.

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Bolts directly to stock mounting positions at the catalytic converter without any modifications required. Doug Thorley Exhaust Systems employ factory-style hangers for straightforward mounting. Exit pipes are capped-off by a great looking chrome exhaust tip.

The system also includes a high-performance Thorley muffler. Your Doug Thorley Cat-back Exhaust carries a Lifetime Warranty for the original owner!

Your Jeep came with ample horsepower and torque for the average grocery-getter driver. Doug Thorley Exhausts have never been much for average, though. Thorley's decades-long mission has been to make stock exhausts look inferior. This is where Doug Thorley Exhausts come in for your Jeep. Using 16-gauge aluminized steel tubing, custom CNC mandrel bending, and a free-flowing muffler, a Thorley Exhaust adds instant punch at the pedal. It provides loads of low-end pulling torque, too.




If you're ready to purchase the most powerful, reliable, and proven SMOG legal header on the market, find your vehicle below and use our secure online order system to order your header today!

All Cat-Back, and some Thorley header kits may drop-ship direct from Thorley (Summit Industries)!


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Jeep Headers

The Thorley 634Y is used in all 6 cyl Jeep applications.