Doug Thorley Headers 4Runner

 In 4Runner, 4Runner Mods, 5th Gen 4Runner Mods, Off-Road Accessories, T4R Accessories

Doug Thorley Headers for 5th Gen 4Runner

Doug Thorley Headers for 5th Gen 4Runner

Doug Thorley Headers on 4Runner – 5th Gen 4Runner Headers Overview and is the Install worth it?

When it comes to power on a 5th Gen 4Runner, well there’s not much of it. But, we do have plenty of options to increase our horsepower and torque. When we think of power in a 5th Gen 4Runner, we all immediately point to the TRD Cold Air Intake or any intake for that matter.

Then, we might start looking at a 4Runner Cat-Back exhaust system. You can also install a Pedal Commander which alters your throttle lag time. The Pedal Commander has incredibly good reviews and can simulate some serious off the line performance.

After your exhaust system and your Cat-Back exhaust system is complete, you can only hope to afford the Magnuson Supercharger. The 4Runner supercharger obviously takes the cake in terms of 4Runner performance. After reading our article on the Magnuson Supercharger and a general overview on the 4Runner Supercharger, you are probably sold. In the meantime, if you are saving up some money, keep reading.

Let’s not forget about a few other options for 4Runner horsepower; headers. And, Doug Thorley headers for 5th Gen 4Runner to be exact. if you are looking for more power in your 4Runner, seriously consider grabbing a set of the Doug Thorley headers. The Doug Thorley headers are an affordable, very powerful solution for your 5th Gen 4Runner power. They pack a serious punch where your current exhaust system is lacking.

Headers combined with an aftermarket Cat-Back system and a Cold Air Intake will have your 4Runner pushing much cleaner, faster, cooler, more efficient air. All of these systems working together are sure to generate some serious power for our 5th Gen.

What are Headers?

Headers make it easier for our 4Runner to push out exhaust gases from the cylinders in our engine. Headers work by eliminating the manifolds back-pressure. Instead of sharing a common manifold, each cylinder gets its own exhaust pipe.

RWHP (Rear Wheel Horse Power) Vs. Flywheel HP (Engine Horsepower)?

Or, Engine HP vs Wheel HP. What is the difference between engine hp and rwhp? Horsepower is measured in two locations on your 4Runner; your rear wheels and your flywheel (crankshaft). Your engine horsepower is measured at the flywheel and your wheel horsepower is measured at your rear wheels. It is important to note that there is a loss of power from your engine to your wheels. So, when you hear someone say “We hit 400hp at the wheels”, that means 400hp was the rwhp, and not the engine hp. Rwhp is what really matters as that is what is pushing our 4Runner.

Doug Thorley Headers (Smog in California)?

The Doug Thorley Headers are not street legal in California. Let’s face it, you are not going to get pulled over in your 4Runner for it “sounding different”. After you install your headers, you will eventually need to have your 4Runner smogged, exactly 6 years after your 4Runner was manufactured. We have a 2014 4Runner, so we will not need to have our 4Runner smogged until 2020. So, we have about 3 years until we have to have our 4Runner smogged.

02 Sensors and Removing Catalytic Converters (Cats)?

When you install your Doug Thorley Headers, you will need to grab a tuner. A tuner; like the Diablo tuner will program your 4Runner into thinking everything is normal. Yes, things will change. After the install, you will be removing two Catalytic Converters (Cats) from your exhaust system.

Once this happens, your 4Runner will throw off some check engine lights. If you were to run your 4Runner with these check engine lights on and not fix anything, you may have problems.

If these Catalytic Converters are removed and not tuned, your 4Runner will try to fix something on its own and overcompensate here and there for airflow and oxygen. This may be seriously harmful to your 4Runner. So, it is important to get a tuner after your install your Doug Thorley Headers.

Doug Thorley Headers Need a Tuner

As we mentioned above, you will need a tuner. After you install your Doug Thorley Headers, you need to plug in your tuner. Run your 4Runner and let the computer gather it’s new data sets.

Your 4Runner will then download the data to the new tuner you just plugged in. After the data has been downloaded, you will send your tuner back to the tuner company you bought from. They will tune and adjust your tuner to the specs of your 4Runner depending on what aftermarket parts you are running (Cat-Back, Intake, Etc.).

The tuner company will send you back your tuner and you can plug it in. The 4Runner will then pull that data back into the computer and your 4Runner will act like everything is the same. Everything except you will have a brand new set of Doug Thorley Headers and you are pushing another 20hp+!!

Installing the Doug Thorley Headers

Doug Thorley Headers for 5th Gen 4Runner

Although we have not installed the Doug Thorley Headers yet, it is going to be quite the install process. For a projected time, I am thinking it will be along the same lines of the 4Runner Stage 2 Icon Suspension Install. This install took around 8 hours. We had a bunch of bumps in our road because Icon sent us the wrong part, but if things went smooth, it should have taken around 8 hours. For the Doug Thorley Headers, I am projecting a similar time.

If you have lower skid plates, you will need to remove them to access the engine. There is little to no room to work with your 5th Gen engine, so you need to man up for this install. If you have a diff breather install on your 5th Gen, you may have to rework your lines as well. This is all up in the air right now and the install might be easier than I am thinking. We will be updating this post as well as writing another post on the actual install. As always, we will keep you posted

Additional Doug Thorley Header Information

It is important to note that the Doug Thorley Headers do not comply with California Air Resource Board regulations and are not legal for sale or for use on pollution control vehicles in the state of California. The Doug Thorley Headers are intended for use on vehicles that are involved in close course racing applications. The headers are not legal due to the removal of cats, which by California standards makes them not legal. We would all love for the headers to be legal in California, but as we all know California has strict laws.

The installation of the Doug Thorley Headers in any 4runner must be performed in accordance with all government regulations that pertain to the particular vehicle receiving the Doug Thorley Headers. Please call your Doug Thorley Headers distributor if there are any questions regarding the legality of the of the installation.


Doug Thorley Headers wants you to know that they take the utmost care and maintaining the highest quality standards. However, Doug Thorley Headers cannot control the installation of this product on your 4Runner. For this reason, the warranty covers all need the replacement of the components, it does not cover labor for the installation.

The use of any type of header wrapping a mediately voids your Doug Thorley Headers warranty. Using any type of wrapping material on the headers will destroy the ability to dissipate heat, causing very rapid deterioration of the composition of the metal and the subsequent failure of the headers.

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Showing 6 comments
  • Mitch

    Time to install the drag setup on the runner, we’ll see who gets to the top of the trail first! She is no longer a runner, she is a sprinter!

    • Brenan - Trail4R

      Right. Installing the DT Headers would be a substantial increase in power. That combined with an intake and exhaust would be awesome.

    • Protrd

      This is why I love this site. Informative info WITH PICTURES. Come here almost daily to see what I need to do to my rig next! Forever loyal to

      • Brenan - Trail4R

        Yo, thanks for comments man. Yeah, we are pushing to showcase every mod possible for the 5th Gen 4Runner and some. Once we have all the mods covered for the 4Runner, we will branch out into the next generation of 4Runner and start a whole new section of the site for the 6th Gen 4Runner. Hopefully, by the time the 6th Gen 4Runner is around, we will have the 5th Gen covered in detail.

  • Michael Weaver

    I did all these installs on my Mustang. Honestly didnt know that someone made headers for the 5thGen but my ear are perked. Who is the go to Tuner after install? Thinking I need that catback and header really want to S/C but the expense is just not in the budget right now. Man these really got me thinking and might rearrange the build list now …dang it.

    • Brenan - Trail4R

      Yeah, these headers are going to be sick! We will be installing them sometime late December. I just need to find a weekend for the install. After talking with Doug Thorley, they recommended the Diablo Tuner. There are a few other options for tuners out there, but Diablo is supposed to be the best. Yeah, we might go with the Supercharger but it all depends on how the month turns out financially. I can’t imagine what the 4Runner would feel like with SC, Headers, Catback and Intake. WOW.

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