Doug Thorley header install

After 220k miles on my 07 V8, I decided to bite the bullet and buy DT short headers since they are now CARB legal. Really the only options for replacements in CA are OEM or DT. On one hand, you get brand new cats but manifolds that will crack again or you have to re-use your old cats and get good manifolds. I opted for DT manifolds and am hoping my cats aren't on their way out.

Anyway, some takeaways from the project are as follows:

- Ensure you have a second or third car in case things go sideways with the install. I had to rent a car for 2 weeks so I could still get to work and drop my daughter off at daycare. This added just under $500 to the cost
- Removing the old manifolds doesn't take long, maybe an hour per side. To get the passenger side manifold out, you will NEED to raise the motor. Luckily only 2 bolts hold the motor to the frame so this didn't take much more time. I didn't have to lift the motor on the driver side but I did have to undo the steering shaft and front driveshaft from the diff to work in this area.
- My truck has been a California truck its whole life so I had zero issues with seized hardware. YMMV WILDLY especially if you are in the rust belt. I still opted to buy aftermarket locking nuts to replace all of the OEM ones as they are one time use. Kept the studs as they were.
- Making jigs out of your old manifold/cat assembly is a waste of time. Instructions call to remove both OEM manifolds, prep the cats (cut them off the OEM manifold), re-install everything with the DT headers and tighten almost every bolt and nut, mark the headers where to weld, tack both sides really good then remove and fully weld. I would have saved a lot of time not making jigs. Mainly because I could not get the DT headers fit up in the jig once prepped.
- Don't buy cheap stainless steel MIG flux core wire off Amazon. I knew MIG welding would be faster to attach the DT headers to the OEM cat but if I knew how much of a mess it would make, I would have gone straight to TIG welding. And I don't know what I would have done if I didn't have a TIG welder as MIG welding stainless requires a different shielding gas mix than the standard 75/25 Argon/CO2 I had on hand.
- Instructions don't say this but the header slips INTO the cat then gets welded. The header doesn't get welded to the outside of the cat, it will impede flow.
- Not all DT headers may be created equal. After welding the cat on the driver side, I decided to test fit and this is where I found out the EGR tube flange is 3/8" further away from the OEM tube. I could not bend the EGR tube on the engine far enough to get the connection made. I thought I would see what DT had to say about it since it should be covered under their workmanship warranty. They said I could cut the cat off and send the header back to them for fit check but I didn't have time to do this, I was renting a car! I ended up making a custom 1/4" stainless spacer, new custom gaskets and longer bolts (not studs) to be able to bolt it up.
- Installing the rear most manifold nut on the driver side will test all of the patience you have. Since I had 3/8" less room to install the nut on that stud (EGR flange too close), I opted to remove the stud and replace it with a bolt (not ideal) but it's sealed up. There was no possible way to get a nut tightened in that small of an area and even tightening a bolt in that area was difficult and was only reachable to tighten from underneath the truck with a flex head ratcheting wrench (3 clicks at a time)
- Buy all new exhaust gaskets prior to install
- Once installed and you are ready to torque everything, you won't be able to fit a socket on more than half of the manifold nuts, only a combination wrench. Good-n-tight will have to suffice for these.

Important tools-

Torque wrench
Breaker bar and a good socket for removing the OEM manifold nuts, they are tight
Lots of 3/8" extensions, wobbler extensions preferred
External Torx socket set for swapping EGR studs to the DT headers or removing OEM manifold studs
TIG or MIG welder capable of welding stainless
Universal joints for 3/8" ratchets
Flex head ratcheting 14mm combo wrench
Long 14mm combo wrench
Reg ratcheting 14mm combo wrench
Grinder with cut off and flapper wheels

All that being said, it may have been cheaper to have someone else install them but I am a control freak and must do things myself so here we are Definitely not a job for most people, I would say. But to get rid of the cold start tick, it has been totally worth it.

 

1. Jesus that seems like a difficult installation

2. Any noticeable power gains?

 

Yeah it was not a fun one. Big v8 in a small mid size vehicle doesn’t leave much room for everything. As for power, it definitely feels like it has more than before with the pluses of being smoother and quieter at full throttle. My stock manifolds made a bunch of noise at full throttle from the manifold cracks.

 

Great insight! I have a set of those short tubes on the way for my '08. I'm impressed the removal only took you about an hour. I've been going back and forth with my mech trying to decide between welding directly to the cat or welding flanges to both ends and mating that way. Idea being that if the cats go bad down the road, we can weld flanges to the new cats and just pop them in rather than removing the whole manifold.

How many hours do you think the job took you start to finish? Book calls for 14.5...
Do you happen to have any pictures of one of the manifold + cat welded pre-install?

 

Flanges wouldn't be a bad idea for serviceability later. I couldn't even say how long it took start to finish, I was so fed up with the job by the time I was finished lol. Best pic I got with the cat and header TIG welded together with stainless rod, might be interesting to try and fit flanges in there, not too much room between the O2 sensor and cat itself