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Discussion Starter · #1 ·
Doug Thorley THY-289Y-C, Tri-Y, installed and fired up. Off to the muffler shop next week.

As a reminder and as I mentioned in my Header Fails post, the starting point Car Info is:

- 1965 GT FB, orig. 289 4V and T10 4 speed still in car, original style suspension, manual steering, added factory AC.
- Original 2 owner car, I’m owner #2 for last 27 years, 67K on the car when I got it, I have the original Window Sticker.
- Original exhaust system (minus resonators).
- New motor mounts, even though what was on was in good shape and I had done the bolt through trick to keep them from separating or sagging.
- Export Brace and Monte Carlo Bar have been car since about 75K.
- Replacing due to DS exhaust manifold cracking all the way through between #6 & 7 on way back from road trip from Nor-Cal to Minnesota and back in June. Had some Flowmaster long tubes in a box so decided it was time to put them on and replace original mufflers since one was developing a hole.

Fail #1 Flowmaster part #814211, full long tube.

Fail #2 Doug’s part #D690YS, Tri-Y.

See Header Fail post for more details on those.
https://forums.vintage-mustang.com/...ils-flowmaster-doug-s-headers-really-fit.html

SUCCESS with Doug Thorley part # THY-289Y-C, Tri-Y Ceramic Coated. Made in the USA.
1964-1968 Ford Mustang 260-302W Long Tube Tri-Y Headers

Note: Requires use of Hi-Po Z-Bar. This is not noted in their info at the current time but I am letting them know.

Looks to be a very well-made set of headers, good welds, etc. Thickest tubes of all 14 Gauge, 3/8” Flange, 1 1/2” Primary tubes, 2 1/2” Collectors. Actual good quality useable gaskets for both at the heads and collectors included. Lifetime warranty on headers, 1 year on coating.

Passenger side fit super easy. Lots of clearance from starter, looks like there should not be any starter heat issues. Collector location is exactly where it should be.

Driver side took a little more work to install but still the easiest of the 3 sets I tried. The motor mount heat shield and motor mount bracket to shack tower were the hardest parts to get past.

Do’s when installing: (note: I used a 4-post lift for the installation, don’t hate me, gift from my late Father)
- Loosen the motor mounts to raise the engine as close to 2” as you can. Watch your fan, you may need to remove it to not hit the shroud.
- I removed the nut on the bottom stud of the motor mount that attaches it to the motor mount bracket on the shock tower.
- Loosen the tranny mount bolts too. Otherwise you are stressing that mount when raising the engine.
- I used a bottle jack and a 2x6 under the oil pan to gently, slowly raise engine. Got the MM stud about even with the top of the hole it goes in on the shock tower MM bracket, maybe even slightly above.

I did the DS first:
- Kept the nut barely on the PS MM stud to help the engine rotate a little clockwise to create more shock tower clearance on the DS.
- Had to remove the MM to Shock Tower bracket from the shock tower (required removing the oil filter to get bolts out)
- The motor mount heat shield could be removed to make installation easier but that could be a pain to get back in after the header is in. You could just bend it down a little then back up later.
- The tightest clearance on the DS was at the bellhousing (pic). Might be an issue for T5 and AOD swaps, call and ask them.

PS went in very easy, nothing special. Both MM stud bolts off when raising to install PS. I’m wondering if the engine even needs to be raised for the PS to be installed.

Z-Bar Notes:
- Standard Z-bar will interfere with secondary tube. The Hi-Po Z-Bar is required. The Doug Thorley info does not note that at the moment but it will be added now that I let them know.

Clutch fork spring note:
I relocated the forward mounting point of the clutch fork return spring from the factory slot in the shock tower to a bracket that I made that mounts to the lower inner bolt of the 3 that hold the MM bracket to the shock tower. That helps the spring not rest against the secondary tube and also clear my Opentracker rod-end clutch linkage.

- All the flange bolts were easy to get to and I could get a 7/16 box end on all the bolts (using Stage 8 locking bolts).
- Spark plugs all easy to get to. I was even able to use my big old Craftsman 1/2" drive ratchet on all but #4. For #4 I was able to get the spark plug socket with a hex end on it and finished it off with a box end on the end of the socket.
- All of my straight plug wires cleared except #4 was a little close so I put some heat shield sleeve in it. It’s kind of a fat boot on my wires.

Again, I like the quality of these. Little things like the 3-bolt flange on the collector being set with a bolt at the top to help with ground clearance, surfacing of the mating face of the collector and reducer very clean and flat, actual good quality usable gaskets.

I didn’t measure it to double check but when I asked about ground clearance was told they are only 3/4" below the frame rail. They are nice and high.

I would buy these again in a minute.

For you guys that have modified engines they also make headers for:
- 1966-78 Shorties
- 1967-70 5.0 and Coyote Swap Tri-Y
- 1967-70 351 swap
- 1964-66 351 swap
- Maybe some other applications too?

For you DIY guys they also make DIY kits in steel and stainless. The way it was described to me was the kits include even more parts then you need. This kit is made to help out with various aftermarket heads.

Of course, I can only speak for the THY-289Y-C, Tri-Y that I put on my basically stock ’65.

Any question call and talk to them, they are very helpful. 1-800-347-8664

I talked to Mike Johnson, sales manager. He was a big help, and a 5th generation Marine.

Feels good to be off the Header Merry-Go-Round.
I likely do some replies to my own post to be able to post lots of pics.

Hope this helps you all.
 

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Discussion Starter · #2 · (Edited)
Some more pics.
My original non-Hi-Po Z-Bar on left, Hi-Po Z-Bar(minus the pin and block I knocked out for using Opentracker rod-end clutch linkage on right.
I also centered the engine while the MM stud bolt nuts were still loose.
Don't forget to re-tighten your tranny mount bolts too.
 

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Discussion Starter · #3 ·
One more pic of the bellhousing clearance.
 

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Awesome. I had a feeling those would fit as I have them on my '68 (289, small block C6).
I kept my mouth shut on your other post because I know you have a manual trans.

Thorley didn't know the 289Y's fit on my application...... so your detail about the hipo z-bar
will also be news to them I'm sure.

Doug's Headers and Doug Thorley DO have a business connection.
Doug and wife Betty sold the original 50's version of the company (Headers by Doug) and got
divorced and the new owner Micky then called it Doug Thorley Headers.
Micky's health went downhill and he asked Betty to come back and help him run the company.
Doug came back onboard to do R&D. Eventually there was another falling out between Doug &
Betty and Doug left to do his own startup..... under the "Doug's Headers" name.
Nowadays, Doug's Headers is owned by Pertronix and Doug Thorley is owned by Summit Industries
in Corona CA. (no connection to Summit Racing) Summit Ind also owns Jardine Headers.
 

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Discussion Starter · #8 ·
One more installation detail.
I removed the DS valve cover to help on that side. Vintage cast aluminum Cal-Custom valve cover. The DS is a little of a more vertical up and over move, so getting the lip of the VC on that side out of the way helped.
 

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Awesome. I had a feeling those would fit as I have them on my '68 (289, small block C6).
I kept my mouth shut on your other post because I know you have a manual trans.

Thorley didn't know the 289Y's fit on my application...... so your detail about the hipo z-bar
will also be news to them I'm sure.

Doug's Headers and Doug Thorley DO have a business connection.
Doug and wife Betty sold the original 50's version of the company (Headers by Doug) and got
divorced and the new owner Micky then called it Doug Thorley Headers.
Micky's health went downhill and he asked Betty to come back and help him run the company.
Doug came back onboard to do R&D. Eventually there was another falling out between Doug &
Betty and Doug left to do his own startup..... under the "Doug's Headers" name.
Nowadays, Doug's Headers is owned by Pertronix and Doug Thorley is owned by Summit Industries
in Corona CA. (no connection to Summit Racing) Summit Ind also owns Jardine Headers.
Holy bed hoppers batman! That's confusing!!
 

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Great pics 1965GTFB and great write up, we should ALL report our successes like this. Wow there's just not much margin for error is there? There should be a sticky with header examples like this that fit so perfectly, such a battle finding the right ones. Have you run it? Does the header ever hit the BH?

Another big question: in some of your pics the headers look like they tuck PERFECTLY up almost completely above the subframe rails, is that for real? Then one pic it looks like the flange drops WAY below the frame? Illusion? Is this about the best ground clearance we're gonna find?
 

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Discussion Starter · #13 ·
Thanks for the great write up. Looking at them, it appears they'll work with GT40P heads great.
I would call and check with them first. I don't know enough about GT40P heads to know.

I just called yesterday to let them know about the Hi-Po Z-Bar requirement and they have already updated that info on the web-site. That's a responsive manufacturer/vendor.
 
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Discussion Starter · #14 ·
Great pics 1965GTFB and great write up, we should ALL report our successes like this. Wow there's just not much margin for error is there? There should be a sticky with header examples like this that fit so perfectly, such a battle finding the right ones. Have you run it? Does the header ever hit the BH?

Another big question: in some of your pics the headers look like they tuck PERFECTLY up almost completely above the subframe rails, is that for real? Then one pic it looks like the flange drops WAY below the frame? Illusion? Is this about the best ground clearance we're gonna find?
I did run it. I didn't stick my head under there (would want ear muffs to do that), but I don't think they are hitting the BH for a several reasons. 1st-the block, BH & tranny should all be moving together since they are pretty solidly bolted to each other, so that gap wouldn't change, 2nd-the gap is probably a little bigger than the pic makes it look, 3rd-when it was running and revved I didn't hear any funny noises.

They do tuck up pretty tight. The pic I took from the side probably doesn't do them justice. You can see by sighting across to the other sub-frame that I actually took it from too low of an angle. If I had taken it with the 2 sub-frames planed into each other they would show even less hanging down. When I called Doug Thorley and asked how low I got an immediate answer of 3/4" below the frame rail.
Here is a pic from my floor cleaning that gives another angle to help see how high/low they are.
 

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I would call and check with them first. I don't know enough about GT40P heads to know.

I just called yesterday to let them know about the Hi-Po Z-Bar requirement and they have already updated that info on the web-site. That's a responsive manufacturer/vendor.

The plug angle on the GT40P head is more perpendicular. Pretty much what I observed on my car with the MAC headers as long as you can get a deep socket on the rear tube of each cylinder on the driver's side you should be fine. Most headers the tube rolls right over the rear bolt which is the place where the plug lies.

My MAC's we're designed to fit the P head and while not perfect it's doable. I believe from looking at your pictures these would be a better option.
 
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