Doug Thorley Headers 4Runner

 In 5th Gen Mods, Accessories, Off-Road

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 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, we all immediately point to the Magnuson SC or TRD Cold Air Intake.

Then, we might start looking at a 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 supercharger obviously takes the cake in terms of performance. After reading our article on the Magnuson Supercharger and a general overview on the 4R 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 horsepower; headers. Doug Thorley headers to be exact. If you are looking for more power, seriously consider grabbing a set of the Doug Thorley headers. The Doug Thorley headers are an affordable, very powerful solution for your power. They pack a serious punch where your current exhaust system is lacking.

Buy a set of these headers:

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

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 4Runner smogged, exactly 6 years after your manufacture date. We have a 2014 4R, so we will not need to have our 4R smogged until 2020.

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

If these Catalytic Converters are removed and not tuned, your ECU 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 DT 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 tuner gather it’s new data sets.

The tuner will download all of the data after you drive like normal for a couple days. 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 ECU will then pull that data back into the computer and then no more check engine lights.

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 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, 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.

Love the 4Runner Lifestyle?


Join the 5th Gen 4Runner community and get access to new gear, specials, free stickers, free decals, step by step installs and much more. Get access to manufacturer discounts, sales, coupon codes and so much more.



Recommended Posts
Showing 19 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

        Yeah, we are pushing to showcase every mod possible for the 5th Gen and some. Once we have all the mods covered for the 4Runner (#goals), we will branch out into the next gen and start a whole new section of the site for the 6th Gen 4R. Hopefully, by the time the 6th Gen 4R 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.

  • Tyler Blomdahl

    Do these headers fit on a 2017? And do you have a link? I wasn’t able to find them for 2017 on DT site. Thanks for all the extensive write-ups!

  • Blake

    What tuner are y’all talking about. I can’t find one that supports the 2013 and up 4Runners.

  • MotoJB

    Why does Diablo Sport not even mention the Toyota on their site? What did I (or you) miss since posting this? Thanks.

    • Brenan - Trail4R

      Good question.
      That is who DT initially recommended for a tuner. But, you are right. I will reach out to DT or you can and see what they say.

  • scott popma

    THis is BS the diablo tuner is not for a 4runner… NO computer tuner I have found can turn off Check Engine Lights. If you are eliminating Cats, you need simulators.

    • Brenan - Trail4R

      Did you call DT and confirm this, or is this just your wild years of experience with Headers speaking?

  • Scott

    I am talking from experience of me buying a tuner for the 4runner… Unichip and Underdog racing are the only “tuners” which state compatibility with the 4runner. Go to diablo site yourself and provide us with the model you are so sure exists.

    • Brenan - Trail4R

      Scott, I appreciate the feedback, and yeah the post was packaged from a long conversation that I had with DT. You just came across like a dick, so I had to as well. No, I have not installed the headers yet. I didn’t have any reason to NOT believe what DT was telling me at the time. Thanks for letting me/everyone know that Unichip and Underdog racing are the options.

  • scott popma

    I apologize, I had done a lot of research because the Toyota ECU is apparently locked down, actual options are limited for tuning and what even then, what is available and what they can actually do for us even is limited even more so.
    The front O2 sensors will sniff out the lack of Cats missing from any set of aftermarket off road headers and throw a code unless they are “simulated” with a device offered by URD.
    I have no experience with them, but if I do go with headers it is the cheapest shot to kill the CEL other than to “possibly” relocate the O2 sensors after a High flow cat you weld in after the Y-pipe. Even with that I am not sure if it would throw a CEL. I’ll let you know how the Y-pipe and Unichip work out.

  • cali

    Any updates on installing the Doug Thorley headers? Thinking about installing them myself, just waiting to hear about your experience with them

    • Brenan - Trail4R

      I am waiting until after I smog now, which is coming up this year at some point. I waited a little too long on that one.

Leave a Comment

Start typing and press Enter to search

Roof Racks for 5th Gen 4RunnerHusky 4Runner Floor Mats Close