Doug Thorley headers and mid pipe, Gibson cat back saga (1 Viewer)

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This post will contain spelling and grammar errors that I may or may not edit once this job is done. But for now I'm on day two (13 hours yesterday and 14 today) of a project that's been sitting in boxes in my garage for a year.

I purchased Doug Thorley long tube headers for the 03-04' gx470 with no secondary air pump tubes. I bought a Hewitt Tech SAIP module to bypass the pump and opted to remove all the associated plumbing. (More on that to follow).

I got URD mid pipes to match to my headers and a Gibson catback exhaust to finish it. My goal was for a nice V8 growl without being too loud and no drone (Time will tell).

Header removal was atrocious. I've done Jeep headers, BMW M3 headers, Audi S4 headers so this job is not foreign to me. Lexus just seemed to put every suspension component and wire loom in the way of all the header bolts. I followed the instructions and started on the passenger side. It was a nice warm up for how s***ty the driver side was going to be. Passenger side came out in about 3 hours. Driver side took about 7 hours. I had 3 nuts strip on the driver side and of 7 of the 8 manifold studs backed out.

A thin wall long neck spiral extractor for the stripped nuts off after lifting the engine gave a straight line to the bolt. Fan shoud will contact the fan and one will break so don't try to hoist the engine more that 2" without removing the fan or shroud.

I replaced the studs that backed out with M10x1.25 studs of the same length and opted for JIS stainess notched flange nuts. I'll do a dab of red loctite on the bolts as blue with burn off with the manifold heat.

Problem I discovered once the headers were ready to reinstall is the 05-09 with the exhaust tubes actually have ports in the cylinder heads, not ported from the headers. This means I'll have open ports, which is a no-go. I send the headers I got a year ago back, which is a no-go. Or, I template the gasket, cut steel blockers and weld them to the header. I opted for "C".

I used the gasket as a template (rough face towards the header). (Made that mistake once!). Once I had my piece cut, I clamped the header to my table, aligned the blockers, clamped those (to prevent warping) then tacked them down.

Once cooled, I pulled them, test fit to ensure the ports were covered, then clamped everything back up and ran beads. I'm using flux as I'm out of gas and some research said it's better on stainless, but who knows, and it's all I had. Penetration looks good and the welds look solid. I'll finish header #2 tomorrow then start reassembling.

I have a 250 amp alternator getting delivered tomorrow that will go in while there's access also. Then I'll install the air pump module and start her up. Fingers crossed.

Additional notes:
When doing this job, make sure you have a healthy selection of extensions and swivel adapters. For me the most common used was 1/2 inch. I have an impact rated 14mm tapered socket that I ground the face down on (removed the bevel from the socket to give better purchase on the nut). This is a must. I stripped 3 nuts before doing this. Also, definitely do not use 12-point sockets on the exhaust nuts, they will strip.

Removing the motor mount bolts was necessary, but I found I did not have to remove the motor mount brackets from the motor side.

I'll add more if I come across more useful tips.

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Damn Sam,
Ambitious! Sounds like you’re winning the fight however...
Good luck, let us know how it turns out and sounds!
 
Welds complete. Steel tabs coated with high-temp primer and header paint in raw aluminum. Not a terrible color match.

The passanger side went in without too much struggle. A second pair of hands would have been nice to align the gasket, but it can be done solo.

The passanger side is 90% on. I have 2 more nuts to thread on. Getting the header seated was an absolute bear! Another hour of wrestling with something that seems like it wasn't meant to fit in such a tiny space. Also, on the driver's side, it seems each header tube is place directly over the stud/nut. My guess is there isn't a lot of options. I'm absolutely not a header fabricator but if I was offering feedback, it would be align the pipe to allow access to the nut with something other than a Barbie wrench.

The last two pictures show a top down, then straight on view on 2 of the nuts. The farthest right is far worse but I cant fit a camera in there.

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I did the driver side with direct replacement and it literally took me like five days 2 to 3 hours each day. I still have the passenger side to do but it is supposedly easier. Be glad you didn’t have to deal with trying to put the pipe on for the damn air pump. I ended up using a Erwin stripped nut removal set that really worked well
 
My air pump pipes nuts zipped right off. Lucky me!

Headers are in. I'm wrestling with the mid pipes now. I do need to correct my earlier post though - I forgot that I actually went with the Doug Thorley mid pipes too. Not the URD versions.

I may need to clock the flange on the driver's side mid pipe. Out of the box it's hitting the driveline. There's a bit of twisting I can do to see if I can squeeze enough room out of it, but I'm thinking I'll be cutting the flange off, clocking it then rewelding. I'm stopping for a beer and to regroup.
 
Just wanted to update this thread with some findings.

This project took more time than expected due to some fitment issues associated with using 03-04 headers, my schedule, and what as best I can tell was a poorly clocked mid-pipe flange of the Doug Thorley mid-pipes.

I have been through several evolutions with this set up and have done a fair amount of parts swapping. To give context, I'll lay out the set ups I went through since I started this thread.

First I ran the Doug Thorley long tube headers, Doug Thorley catless mid pipes and a Gibson exhaust. This is designed to be a bolt up system. I had to cut one flange on the driver side mid pipe, turn it about 20* and weld it back on. Not a huge deal but took time and killed the bolt on alure. I didn't want to run with no cats, so I welded a freeflow cat into the post mid pipe section before the muffler. This system was WAY too loud. It droned on the freeway. Performance was terrible until about 4.5k rmps. It had to go.

Next change was adding a small resonator after the cat. This made barely any difference but I felt a slight increase in low end torque, leading me to believe an expansion chamber would help.

I toyed around with the idea of getting a different muffler, then decided to measure the piping of the factory mid pipes with cats. There are several reducers in the pipe and the flattened out section of pipe. I measured the circumference of the flattened section and found it to be the same diameter as the Doug Thorley mid pipe tubing. I'd read that the flattened section is actually an outter sleeve, but as best I can tell without cutting it open, it isn't. Based on the cells in the secondary cats, they seemed to be in great condition, looked to flow well compared to the free flow cat I installed and obviously took less abuse that the primary cats. They seemed like they would provide the expansion chamber I needed.


I reinstalled the factory mid pipes and the sound is just what I was lookimg for. Throaty at WOT but mellow at idle. The low end torque is significantly improved over the previous set up.

My final thoughts are the headers are worth the hassle. The factory mid pipes are well designed and replacing the factory muffler with a free flowing muffler would probably be just fine for a nice sound and much better performance. I did this mainly for fuel economy and ground clearance. I'll know more about the fuel in a few tanks.
 
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I appreciate the write up. Indeed the DT longtubes are not an easy install and I too had to cut and weld the flange on my driver's side OEM mid pipe flange to get everything to "bolt up". I've been doing my exhaust in stages so my system header back back is OEM. The next step for me was going to be the DT midpipe and the rest of the exhaust OEM but now reading your post I'm second guessing that. At first glance that 2-1 collector area on my OEM mid pipe looks like it belongs on a Corolla which almost makes me thing I'm not using the full potential of the headers. I also dont want my truck to sound like a NASCAR. The one thing I noticed in your photos is the size of your (2005+) 2-1 collector. Yours looks larger than my (2003-2004). Do you have that measurement of yours at the flange by chance? I'd like to measure mine to compare. Any advise would be great. Thanks in advance!
 
Sorry - I don't have the measurement. I'd grab it for you but I'm on the east coast for training for another 10 weeks.
Remind me early March and I'll get you a number.
 
Sorry - I don't have the measurement. I'd grab it for you but I'm on the east coast for training for another 10 weeks.
Remind me early March and I'll get you a number.
hey dude! its march!

:D


im getting ready to do this myself...but im completely looking for that annoying, overly loud v8 sound. :)
 
hey dude! its march!

:D


im getting ready to do this myself...but im completely looking for that annoying, overly loud v8 sound. :)
Due to covid, I got extended down here. I'm not heading home until the end of the month. Good memory though!
 
I appreciate the write up. Indeed the DT longtubes are not an easy install and I too had to cut and weld the flange on my driver's side OEM mid pipe flange to get everything to "bolt up". I've been doing my exhaust in stages so my system header back back is OEM. The next step for me was going to be the DT midpipe and the rest of the exhaust OEM but now reading your post I'm second guessing that. At first glance that 2-1 collector area on my OEM mid pipe looks like it belongs on a Corolla which almost makes me thing I'm not using the full potential of the headers. I also dont want my truck to sound like a NASCAR. The one thing I noticed in your photos is the size of your (2005+) 2-1 collector. Yours looks larger than my (2003-2004). Do you have that measurement of yours at the flange by chance? I'd like to measure mine to compare. Any advise would be great. Thanks in advance!
What's your opinion of the sound with the long tube headers, followed by the OEM midpipe and muffler? That's the route I'm thinking of taking.
 
Due to covid, I got extended down here. I'm not heading home until the end of the month. Good memory though!
Sorry to hear about your extension Brother, dang.. There goes some valuable wheeling time!

Anyways.. Glad you're happy with your mod, good stuff! If you had to do this project again, what would you do different? I'm thinking bout giving it a go myself..
 
Sorry to hear about your extension Brother, dang.. There goes some valuable wheeling time!

Anyways.. Glad you're happy with your mod, good stuff! If you had to do this project again, what would you do different? I'm thinking bout giving it a go myself..

I'd definitely skip the catless mid pipes. The GX was just absolutely gutless until about 5-6k rpms, which is not where you want your power in this type of rig.

I'm not sure the short tube/cat headers with a catless mid pipe wouldn't be a better choice to build some low rpm torque. Hard to say... I'm planning to ad an intake and see if it lets the engine breathe any better. Normally I wouldn't bother with an intake, but with the headers, I'm thinking it might be an improvement.
 
I'd definitely skip the catless mid pipes. The GX was just absolutely gutless until about 5-6k rpms, which is not where you want your power in this type of rig.

I'm not sure the short tube/cat headers with a catless mid pipe wouldn't be a better choice to build some low rpm torque. Hard to say... I'm planning to ad an intake and see if it lets the engine breathe any better. Normally I wouldn't bother with an intake, but with the headers, I'm thinking it might be an improvement.

Almost a year later....how's it all holding up?

Would you do it all over again or go about it differently? Did you ever do a free flow exhaust?

Any "seat of the pants" performance improvements or just improved sound?

Any measured fuel economy savings?

Thx!
 
Things are holding up just fine. I'm not sure how long ago it was, but I ended up reinstalling the factory mid-pipe to have the OE cats to provide some resistance to the exhaust flow. I just recently had the time to source some universal 2.5" cats and weld them into the URD mid-pipe. I replaced my exhaust gaskets, which seems to have cleaned up an exhaust leak I had.

This current setup seems to sound the best and offer the best performance upgrade.

I didn't discuss it much, but you can see a cat back exhaust pictured in my original 2020 post. That's the magnaflow overland system. It's been on the GX since I originally started this process.

It's nice and has a decent rumble, but the quieter the better for me. I'm not looking for an American V8 sound, so I'd appreciate if it was a bit quieter. But it gets the factory duffle bag of a muffler out from under the truck and saves weight, which was a huge factor for me.

Regarding fuel economy, there's no way my set up would give a decent point of reference. I'm on 35's, I run 4.56 gears, I have front and rear steel bumpers, a fridge, drawers, armor, ECT so my MPG is atrocious, but not unexpected. That said, if you have the same set up and want to install headers, I average in the low 13's.


And before anyone points it out, I know the heat shield should be between the cat and the body. I had to install them this way for the clocking of the 02 sensor body.

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Hey - apologies if this is a stupid question, but trying to better understand how an exhaust setup like this works. @ArBrnSnpr i think you’ve got the long tube headers, yeah?

Doug Thorley headers are likely my “big budget project” this year.

Looking at the short tube so I can cover my ass for emissions compliance more easily.

Thinking about parts from front to back:
- headers (dt short tubes)
- cats welded to headers
- y pipe to rear of cats (looking at urd)
- cat-back exhaust (looking into magnaflow overland)

Aside from gaskets and stuff, this covers parts, yeah? Totally new to exhaust setups.
 
Doing the same, short tubes but will be keeping the stock exhaust because it’s pleasantly quiet.

If you want a budget ‘overland’ exhaust, just move the tailpipe. The marketing of the notion that you need a special exhaust for overlanding is a tad absurd.
 
I have the DT LT's, and the rest of my exhaust is 100% stock. There is almost no difference in sound than stock, and way more power. Since I'm nearing 40 and my GX is my daily, I really don't have an interest in it being any louder. The LT's gave it a really nice power upgrade, definitely "feels" like 30 or so more HP. Gas mileage is pretty much unchanged from stock.

A better sound upgrade is a cold air intake, which is nearly silent at light throttle, but provides a really nice growl at higher levels of throttle (I have one and really enjoy the sound).
 
I have the DT LT's, and the rest of my exhaust is 100% stock. There is almost no difference in sound than stock, and way more power. Since I'm nearing 40 and my GX is my daily, I really don't have an interest in it being any louder. The LT's gave it a really nice power upgrade, definitely "feels" like 30 or so more HP. Gas mileage is pretty much unchanged from stock.

A better sound upgrade is a cold air intake, which is nearly silent at light throttle, but provides a really nice growl at higher levels of throttle (I have one and really enjoy the sound).

Still running all original cats (i.e. no cat deletes)?
 
Just the two secondary cats in the Y pipe. The two primary cats have to come off to fit the LT headers.
 
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