S197 @4o6racing Build Thread Profile - S197 Mustangs

[67GTA]

Way past due for an update here! After having the entire winter to work on upgrades, my typical procrastination held true. The overarching goal of the offseason upgrades was taking weight out of the car, while simultaneously upgrading the brakes.

With rear calipers getting harder (and more expensive) to source, I set out to find an alternative solution. The floating style caliper required for the solid rear axle greatly limits options. Further matching the hydraulic volume of the stock caliper narrowed the choices even further. Ultimately landed on a 2-piston Wilwood GM Metric caliper. Brake pad options are plentiful, and these calipers have been race proven for 35+ years. With lots of help from @DipstickMotorsports and @LIGISTX, the rapid prototype process was launched.



The arc length of the pads weren’t perfect with the GT500 rear rotor that I was running, so decided to make the switch to the OE size Girodisc rotor. A 2nd prototype bracket was printed and test-fit, and with a few final tweaks, the file was sent off for milling. A donor rear end was sourced, swapped with a Torsen T2R and 3.73 gears. Net weight savings from OE calipers/GT500 Girodisc to new setup: 15 lbs







To complete the brake upgrades, the front kit that’s been on my list for years was on a killer Black Friday deal. Net weight savings - 9.6 lbs.



The final piece to the weight loss plan was carbon fiber doors from Chicane 23. The door glass was left in after cage install, mostly because I tow the car on an open trailer. With the car staying in a garage at the track now, the weight penalty was no longer worth keeping the glass for the occasional trip back to Montana. Net weight savings: 98 lbs!!!

Removing the Steeda jack rails added another 15 lbs of reduction, bringing the offseason total to 138 lbs, which brought the car back to optimized for the TT3 power/weight ratio. A few delays with parts and a busy work schedule had me miss the first 2 rounds of the NASA season, but the wait would be worth it!

 

[67GTA]

First shakedown and competition event with the new changes was mid May. Round 3 for NASA Utah, so starting out my season in the hole to the other TT3 competitors. Outer loop was the configuration for the weekend. I must admit, the first send down that long straight into T1 brake zone was a bit scary, hoping that our homegrown rear brake setup was up for the task! The setup performed flawlessly. In fact, so well that I was over-slowing every corner while relearning deeper brake points.

After a couple sessions, the wear pattern on the new rears was exactly what I’d hoped for:



Friday test sessions were my first experience on Nankang CRS. I chose these as my test day, fun lap tires for this season because of their heat resistance and long life. The deep tread seemed a bit squirmy for the first couple heat cycles, which checks out with what I’ve heard on these. As tread depth comes off, I expect the tire will get faster. Very happy with the choice, and lapped within 1 second of last fall’s PB on A7’s.

Saturday morning’s Time Trial session was the first time out on the new Hoosier A8’s. First heat cycle was that legacy purple-crack magic, where the tires feel like Velcro on the track. The result - smashed last fall’s PB by 3.2 seconds!! 2:05.9 was good for P2 in class, and was feeling really good about being in striking distance of the leaders.

I only ran 1 session on Sunday morning before hitting the long road home, and couldn’t quite match Saturday’s pace. 2:07.1 and P3 in class. The drop-off had me wondering if that characteristic carried over from the A7’s, where the first 3 HC’s are money and then quickly decline from there.

The car was running great, but still fighting random misfire codes and was still running hot on CHT and coolant temps. Need to diagnose a few things before next round, but otherwise optimistic about the improved pace from last fall.

 

[67GTA]

In an effort to track down the random misfires, I decided to change to a new set of injectors and also replace spark plugs. The #8 plug was the first major clue to the issue. The threads were rusted all the way to the conical seat. Ugh.



With only a few days until next event and a pretty grim outlook on underlying issues, the clear choice was to send it, see what happens and collect as many points possible.

Round 4 was East configuration, which is the tightest, most technical of the options. With no practice on Friday, I decided to turn multiple laps in the first competitive session on Saturday and see how the A8’s would respond over multiple laps. First flyer was just a bit off my PB from last season, so I was pleasantly surprised when the 2nd flyer improved by a lot - down to a 1:41.93, almost 2 sec. improvement from last fall!! With temps creeping up, I opted to keep rolling for a 3rd flyer, which the lap timer had me in the green again. Right up until the final 2 turns when the coolant cap let go and pushed water out the hood vents and all over the windshield. Far too familiar with this situation, and all but confirmed my worst fear that the engine would have to come out. Again. My time held up for a 2nd place finish for the day.

Already committed to the weekend, I opted to hang around and run 1 last session on Sunday morning to get the points. Car ran great for the only flyer I dared, coming within 3 hundredths of the previous day and good for P1!! 1st win with NASA Utah - bittersweet knowing the work that lied between that day and next round.

 

[67GTA]

With a 6 week break until the next event, the window was tight for getting the car back to Montana, parts lined up and getting the engine swapped. The 2-post lift made the job much more manageable, especially fighting 100*+ heat.



Tear down confirmed the issue - cracked cylinder wall on #8. Not just similar to the last cracked block - EXACTLY the same spot. I guess my previous theory of a compromised intake gasket on that runner is ruled out, since this intake was installed with utmost caution and there’s no issue with the sealing. So the issue must be that specific piston, as it’s the common denominator between the 2 engines.



And here’s the cylinder from the last block for reference:




Not willing to try for a 3rd time (insanity), I made the decision to replace the shortblock with an OE Ford Gen 3 shortblock. This was the route I wanted to go back in 2021 during the first rebuild, but covid era shipping had it unavailable when I needed it.

While everything was apart, I took the opportunity to swap out the clutch slave cylinder to the newer Dark Horse part. Dimensions are the same as the GT500, but it’s built with a more robust bearing rated for higher RPMs. I also shimmed the slave out by and additional 4mm based on measurements taken for the air gap. The measurements confirmed the Kohr spacer is too short for the GT500/HyperSingle combo, and likely the reason I’ve had a couple CSC failures. All needed parts showed up on time, and everything was back together just in time to make the trip back to Utah.

First session Friday would be focused on a break-in cycle to seat the rings. 70% throttle with short shifts, and long decel’s using engine braking. Drove the full 25 minute session and temps were all good. Decided for second session to open it up a bit. Very first hot lap, top end of the straight I heard the worst noise you would ever want to hear at this moment in time. Noticed a quick burst of sparks out the drivers side window and quickly shut it down and headed for off track, fully expecting an oily mess. The track workers confirmed there were no fluids dropping, so I tried starting the engine to see if it would turn over. It fired right up, oil pressure was great, no crazy sounds?? I opted to drive it back in, and shortly after pulling back onto the track the noise was back. It sounded like it was coming from the LF suspension, but steering felt fine. LONGEST 3 MILES of my life!! Jumped out of the car in the paddock - and wouldn’t you know the damn splitter support rods on the front let go!! Never had an issue with these - but they just had to let go on the first WOT pull of a new engine - that’s CRUEL!! Quick trip to Home Depot, and disaster averted.



Ambient temps were well over 100* by afternoon, so not overly surprised the coolant temps were in the high range. Spent the evening making sure I didn’t have an air pocket trapped in the cooling system. Also ran the Crank Relearn process as I forgot to do it after the first fire-up, and the car threw a few random misfire codes in the afternoon.

The rest of the weekend went great. No more misfire codes, temps stayed manageable and everything performed perfectly. My best time on Saturday was a 2:06.7, about 8 tenths off my PB, but pretty happy considering the heat. That held up for P2 on the day. Sunday started off even better. Using the previous knowledge that the A8’s are good for more than 1 lap, I took advantage of leading the field out for the session. Open track, mechanically sound and pushed for a 2:05.21 on the 2nd flyer lap, beating my PB BY 7 tenths! Two things that would never happen with A7’s: PB on a 2nd flying lap AND on the 9th heat cycle of the tire. Huge improvement in my opinion. Finished the day P1 for the second win of the season.

Here’s Sundays lap: