S2's Build Thread


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I started fabricating the cat-back exhaust system. The plan is to fabricate stainless steel sections for the catalytic converters (cats) that connect to the merge collectors and titanium mufflers via v-bands. My engine builder recommended an Air-Fuel Ratio (AFR) of 10.5-11 which is crazy rich and will quickly burn out any cat. I’m going to try running cats with a leaner AFR. To provide the best chance of success, I purchased G-Sport catalytic converters which are EPA compliant and support up to 850 HP each. Worst case, I’ll have to replace these sections with resonators. Time will tell.

I purchased 321 stainless steel transition cones from SPD to adapt the 3” merge collector outlets to the 4-1/2” cat ODs. I used a hydraulic press, a die, and 3-1/2” 321 stainless steel tube to fabricate transitions from 4-1/2” cat OD to the 3-1/2” down stream exhaust. Abe welded the transitions and tacked an elbow section and a flange.


Catalytic converter welded to transitions, elbow and flange are tacked; customized Vice Grip with v-band jaws

Mr. Miyagi would have found automotive fabrication great training — you know the whole Wax On, Wax Off thing. Parts come on and of the car many times and it makes sense to find ways to make that process easier. For example, I swapped all of the suspension nylocs with plain nuts for the build phase. Abe modified a Vice Grip to have v-band jaws as shown in the picture above. The cats have already been in-and-out a dozen times (times two because there are two sides) and it’s already saved a lot of time and we’re no where near done.


Left catalytic converter


Right catalytic converter

I’m going to install cutouts before the cats and I purchased several to figure out which would work best. I selected 2.5” cutouts from DPW. Although the exhaust is 3.5” there is no need to have the cutouts be that large because the exhaust will take the path of least resistance. The worst case is that some exhaust flows through mufflers and the car isn’t quite as loud. DPW provides an inlet tube and a turn-down tube, neither of which worked for my situation. No problem, I’ll make my own. The challenge was that DPW uses proprietary v-band flanges. They’re very lightweight which makes sense because they only need to support a fraction of the weight of a standard v-band. I tried for a couple of weeks to determine if they could provide standalone flanges to no avail. That left me with two options: salvage them or fabricate new ones from scratch.


Inlet tube (left), cutout valve (middle), turn-down tube (right), v-band clamps (bottom)

I went for option one which is a lot less work and requires no additional material. The first step was to cut the flanges from the tube with an abrasive cutoff wheel. Once that was done I chucked the flange in the lathe by grabbing the v-band (as opposed to the tube). Machining relatively thin-walled tube on the lathe is always a little nerve racking so I took a bunch of shallow passes with a boring bar. The flange from the turn-down tube was trickier than the one from inlet tube because the curvature of its tube projected inside the flange. This resulted in a 50% interrupted cut (i.e. cut for 180 degrees and then skip for 180 degrees ). While the sounds made me wince, everything worked fine.


Flange being bored on the lathe, the tube has already been removed


Flange cut from tube with an abrasive cutoff wheel (left) and flange with weld bead and tube removed with lathe (right)

I only purchased one cutout to ensure that everything worked. I need to purchase a second one and repeat the process twice.


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Neil, I'll have the engine tuner ask him when I get to that point... he clearly doesn't want to see cats on the engine LOL

As I’ve previously mentioned, I’m completely changing the rear 20% of the tail. The stock tail is a single pivoting piece that supports the tail lights and has an integrated “diffuser.” This approach is easy to implement, but the pivot motion interferes with the wing and exhaust and the molded diffuser is more of a parachute that anything else. Mine will have a fixed rear bumper that supports the wing, tail lights and a functional diffuser. The engine cover will hinge backwards towards the tail.

About 18 months ago I chopped the tail. Before taking a reciprocating saw to it, I spent some time thinking about how I would maintain the correct orientation once the hinge points were cut off. I welded a temporary support to the top of the rear suspension brace. It has two locating pins (borrowed from the nose) that stick through the tail to index and support it in the middle. From the underside I drilled a hole through the temporary bracket and the fiberglass - this got the X/Y coordinates perfect. I then tapped the bracket, enlarged the hole in the fiberglass and screwed the indexing pins in. By threading the indexing pins up and down I was able to get the Z axis perfect. I then added a jam nut so that it wouldn't move.

While the indexing pins locate the tail they won’t prevent it from deforming when the duck tail is removed due to a combination of the weight of the wheel arches and tension in the fiberglass which is released when the duck tail is removed. To address this, I tapped holes in the tube and installed leveling feet upside down. Since they have a ball socket I was able to get the wheel arches perfectly dialed in. I was careful about how I cut the tail so that I can use the removed piece to validate that everything is where it's supposed to be. As can be seen in the video above, the tail doesn’t deflect when the chopped section is removed.


Temporary support bar welded to top of rear suspension brace; two leveling feet and two indexing pins


Right-side indexing pin (left) and leveling foot (right)


Right-side indexing pin sticking through the fiberglass

With the tail chopped, indexed and supported, I needed to stiffen the engine cover and provide a way to mount the hinges. While the final version will achieve this via carbon fiber tubes and bonded steel plates, I have a lot to figure out before then. So, I welded some right-angle to a 3/4" square steel tube and bolted it to the back edge of the engine cover.

I’ve also started finalizing the tail subframe which is made of 1” OD 0.120” wall 4130 tube. It supports the wing, transaxle oil cooler, rear bumper, tail lights, titanium exhaust, and engine cover.


Tail subframe with temporary wing and hinge mounts welded to clamping two-piece shaft collars

Rather than design and fabricate a hinge I looked for an aftermarket billet one. The majority that I found are for 60s and 70s muscle cars and I settled on 60’s era Mustang trunk hinge. I didn’t want to splurge on the billet version until I had proved things out, so I bought a stamped steel one on eBay. I’m glad that I did because I had to hack their mounting plates to get them to fit around the temporary tube bolted to the back of the engine cover. The hinges have vertical slots to facilitate adjustment so I fabricated some temporary plates with horizontal slots. I didn’t want to tack weld them to the tail subframe so I purchased several clamping two-piece shaft collars with a 1” ID and welded the plates to them. This provides a lot of adjustability and is easy to remove when I fabricate the final version.

I took the same shaft collar and slotted bracket approach to temporarily mount the wing. Once the hinge was mounted I removed the locating the pins and opened the engine cover. It was as smooth as I hoped, but it’s a two-person job because the engine cover has a lot of flex. Once I stiffen it and add air springs it will hopefully be a one-handed, OEM-like exercise.


Engine cover hinged open. The red line indicates where the fiberglass will be sectioned to clear the wheels. That part will be fixed to the rear bumper.

I need to make a big decision on which tail light I’m going to use so that I can begin to finalize the body mods, exhaust and diffuser.
How can I steal all your ideas, if I finish my build first? I love your fixed rear tail section idea, I've been planning to do the same on my car to compliment my custom diffuser, wing uprights and rear bumper. Nice progress Scott on this rolling piece of art. I'm also happy to see you fabbing in some temporary hardware while the final design evolves.


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Mason, it's a lot of work just to mock things. The biggest challenge now is to figure out how to temporarily stiffen the tail so that I can start testing some air springs.


LS engine oil inlet fittings; Daily Engineering (left) and Kurt Urbane (right)

In a previous post I replaced the oil inlet fitting that came with the Daily Engineering dry sump pan with one from Kurt Urbane. I went from colliding with the merge collector to having about 1/4” of clearance. Do’h! That’s too close.

The only solution was to shorten one of them on the lathe. The Kurt Urbane was a better starting point because the hex diameter (i.e., what you wrench on) was smaller, 0.932” rather than 1”, which provides better block clearance, and it has more threads into the block which means that it’s less likely to leak. That said the hex was taller so the first step was to turn it down from 0.366” to 0.311.” I then used a cutoff/parting tool to split the part into two pieces.

I wanted the two pieces to interlock to ensure that concentricity was maintained during welding. Machining the male side was easy to figure out, but I was confused about the female side — some things never change LOL. I’ve done basic boring operations before, but I wasn’t confident that I could achieve the tolerance that I wanted with a perfectly square inside corner. I then figured out that I could load an end mill in the tailstock and do a simple plunge cut. After some consideration I ordered an 11/16” center cutting, 4-flute, square end mill. What I didn’t think about was that its shaft size was 5/8.” The R8 collets for my mill go up to 7/8,” but the Jacob’s chuck in the lathe’s tailstock only goes to 1/2”. So I returned the end mill and purchased one with a 1/2” shank. Despite that setback the second end mill worked great and I got to use the tailstock’s DRO for the first time.


Rod (left/red) pressing part onto the live center (right) to ensure concentricity; and no it wasn’t concentric when I took the picture!

The male side involved a simple turning operation, but setting it up wasn’t as easy as I thought it would be. I could only put 0.1” in the chuck and I couldn’t get the part concentric within the jaw. After some research I figured out that I could put a live center in the tail stock and then push the part onto the live center using a long rod through the backside of the spindle. It would have been nice to leave the live center in place, but there was it was in the way of the cross slide so it had to be removed. I was able to get the part concentric, but after taking a bit of material off I realized that there was too little material for the chuck to grab.

Since the part was made of stainless steel, I lightly grabbed the threads with the chuck and only turned 0.005” (0.010” total) per pass. That worked well and there was no damage to the threads.


Female (left) and male (right) pieces ready to weld


Daily Engineering fitting (left) and Shortened Kurt Urbane fitting (right)

I’m going to have to pull the engine and remove the headers to see if it all works. I think that I might need to modify a socket to clear the block and perhaps grind the block a bit. Time will tell.


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Titanium pie cuts before deburring and surface conditioning and 3D-printed tube clamp

I’m going to run an x-pipe under the transaxle. Since I’m primarily interested in smoothing and reducing the magnitude of the exhaust, as opposed to maximizing HP, I went for what would fit best. The x-pipe is composed of pie cuts sourced from 3.5” OD 0.047” wall Grade 1 titanium tube. They were cut at a 9.5-degree angle on a horizontal bandsaw using the tube clamp that I designed and 3D printed in a previous post. The edges were touched up on a belt sander, the inside edges were where deburred and the exterior face was brushed with a tube sander running a conditioning belt.


Pie cuts tack welded to form the left and right sides of the x-pipe. The sharpie lines on the table indicate the target spacing of the exhaust tips. Note that the pipes have a 3.5” OD and the tips have a 4.0” OD.

The pie cuts were tacked into curved symmetrical left and right pipes. A scrap straight section (not pictured above) was tacked to both ends of each pipe to prevent the end pie cuts from deforming during welding. After welding, the two pipes were scalloped on the bandsaw and tack welded to form an “X.” They won’t be permanently welded together until the rest of the exhaust is in place. That’s a total of 22 pie cuts and 20 welds spanning 78” just for the two pipes!

Pie cuts welded, but the left and right pipes are just tacked

I decided to try heat coloring the scraps from the scallop cuts with a MAP torch. Titanium goes from yellow, to purple, to dark blue to light blue as it’s heated. I cleaned the one on the left with acetone. For the right one, I removed all of the weld oxidation with a surface conditioning before cleaning it with acetone. It looks significantly more blue in person. I’m going to experiment some more. That said, I’m not sure that the cool colors that can be achieved will remain after the car has been run hard a couple of times.

That looks sweet and a lot of fun Scott! And a lot of welding...! How did you guys keep it so clean and free of alpha case when welding?


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How did you guys keep it so clean and free of alpha case when welding?
Abe's a pro so he was able to achieve the results without any special equipment. Edges were deburred, a tube polisher with a surface conditioning belt was used to clean clean the surface, acetone was used to degrease, clean gloves were used, pure argon with a healthy flow was used to back purge and care was taken to ensure that the bead was completely shielded by the cup until it cooled. The low amount of alpha case is due to shielding. While he's used a parts-per-million (PPM) oxygen analyzer at other job to insure a proper shield, he doesn't have one in his shop. Instead he just runs more gas than he normally would. To ensure that the hot bead is always under the cup he closes the doors to prevent an errant breeze, he's careful with torch angle and he only does 10-12 dabs before stopping. At which point he flips his helmet up while keeping the cup over the bead with the gas running for another 15-20 seconds after which he rotates the tube and repeats the process. Given his experience level and that this isn't an aerospace part, he doesn't use a thermometer to determine when the bead is cooled. An excess of argon wastes a little gas and takes a few more seconds per cycle. Too little and you get alpha case.

So in summary, standard TIG welding practices, gas at a higher pressure that what you'd use for steel or aluminum and the patience to keep the cup over the bead until it cools.
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I had figured out how to mount the C7 tail lights and Kevin had sorted out how to fit them into the body. So it’s time to just do it, right? Nope… Brian mentioned the 2020-2021 Toyota Supra tail lights which weren’t out when I settled on the C7 lights. They are more modern, exotic and make the C7 lights look cheap.


The outer top corner has a big radius which isn’t even close to fitting the body. I’ll need to recontour the top corner of the body from the middle of the rear wheel well to the edge of the tail light. There is also a pretty big front-to-back curve which is OK because I’m going to stretch the back of the car 5-6” to make room for the mufflers and a proper diffuser. It will be a lot of work, but worth it in the end.


Note the gap between the top left of the tail light and the body.


The side of the lens will be buried inside of the body

I couldn’t find a wiring diagram or harness part number online so I went to a Toyota dealer. The parts guy couldn’t figure it out either and he asked the techs. To determine the part number for the harness they need a VIN. To get a wiring diagram the car must be connected to their computers! WTF happened to the Right-to-Repair Bill?

It doesn’t look like I’m going to be able to get a sub harness, a pigtail or figure out what the connector is so I’m going to solder wires to the pins and fill the socket with potting epoxy. The first step was to figure out the wiring without letting the smoke out:
  • Big Pin: Ground
  • Small Top Pin: Brake/Turn Light (12V)
  • Small Middle Pin: Running Lights (12V)
  • Small Bottom Pin: Doesn’t appear to do anything, it might be diagnostic related.
The lights look great when lit as seen in the video below.

Kevin did some initial sketches. I need to figure out which direction I want to go…

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