First post- we'll start with my prediction for the STU class at Nationals this year. Out of the people I know that will be competing in the class at Nats that's my pick. Pro driver Bryan Heitkotter bought Brian Peter's 350Z which won the class last year, Lane Borg in his usually prepped to the gills yellow '04 C5, Lugod in the OS Giken USA Red FRC, and Jeff Stuart in a 350Z which I don't know much about. He won a 55-deep C-Street class last year so I can't see him doing worse than 4th.
As for where I think I will end up? My goal is to bag a trophy. Last one available would be fine... I have my doubts about how possible that may be but we will see. First step is to bag a contested trophy at a Tour this year. I "won" A-Street in my Solstice GXP last year at the Atlanta Match Tour but... I was the only one there. Four other tours attended in my autocross career with competition but no hardware. It is a fun car though, I still drive it to work most days, and it was great to learn the ropes with.
Ok, now for the car this blog is supposed to be about. Well, maybe I should start with some more background, why am I building an STU Corvette? Easy! Why wouldn't you build an STU Corvette? But really, my first real autocross car is/was (I still have it) a Solstice GXP I bought 3 months out of school. I wanted something turbo, RWD, manual, and sporty. Didn't consider much class competitiveness or practicality. Found one without A/C and I thought, cool, less work to remove the A/C when I am turning it into a crazy fast racecar! Eventually learned about National level SCCA autocross, got hooked, got destroyed but Junior Johnson in a C5Z06 in A-Street at the Wilmington Tour, drove 7 hours back home in a cramped uncomfortable hot loud car and decided enough of that. I knew I didn't want to keep running the Solstice in the beginning of 2014 so I hadn't been doing any work to it and saved up some dough to buy a new competition car. I wanted to run an ST class I knew, since I like modifying cars but don't have room for a trailer/tow vehicle or even a tire trailer and I'm also too lazy to swap tires at events. Something that I could take to track days would be fun too. They classed the C5 and 350Z into STU at the beginning of 2014 and that immediately caught my eye. A Focus ST or Fiesta ST in STX also would have been interesting but I wasn't sure of how competitive they would be. Someone should try a FiST in STX though, it's very narrow and can make a TON of torque. That 1.6l Ecoboost is a heck of an engine. I ran some thrust curves and estimated how much weight you could drop from a C5 in ST trim, compared it to the reigning top dog GR WRX STi and the 350Z, and was pleased with the outcome. Easy to see how the STAC classed the car in STU since the 2nd gear thrust curve is so much lower than an STi and it is something like 2-3" wider than a Z, but I think the C5 has a lot of untapped potential along with an extremely healthy performance aftermarket. Easy to find Delrin bushings for control arms, huge selection of quality long tube headers, easy to find and fit wide wheels, engine responds well to tuning, lots of choices for fancy dampers, etc. The Corvette forums used parts for sale area is also a treasure trove of killer deals so I could build up a nearly fully prepped car with much less headache and capital outlay than some other platforms. I also like GM sports cars and LS1 engines so it was an easy choice. Let's find one with A/C this time too.
August 2014, I've been spending quite a bit of time searching Autotrader and craigslist for suitable candidates. Found some that look good but didn't quite have the money yet or they were far away, but then one pops up on craigslist in Shelby, NC. A '99 FRC with 59k miles, few options, pretty much bone stock. Turned out to be a pretty old guy that was having a hard time getting into the car anymore since it was low and didn't drive it much. He was super anal about cleaning it and never took it out in the rain. I told him I'd take good care of it, didn't want to go too much into all the cone marks and track slag it would be collecting shortly... Picture below is the car right after I got it.
I picked it up on a Thursday or something and there was an autocross at zMax in Concord the following Saturday. It still had Michelin run-flats on it with date codes from 2004 on the front and 2008 on the rear... yeesh. Needless to say they didn't work very well. I don't think I learned anything about driving it. Nowhere to go but up from there though. The North Carolina Autocross Championships were coming up in 2 months or so and I wanted to have a good showing in STU. First step was to ditch those awful run-flats. Enter ebay and the autocross forums, and I was able to grab a set of 4 18x10.5" C5Z06 rear wheels and 4 275-35-18 BFG Rivals with decent life left in them, all for a very reasonable dollar amount. Car looked pretty good on them too, and the difference in grip and steering feel from those run-flats was simply astounding.
Picture above is from a drive I took in the NC mountain back roads with some buddies. The M5 was having a hard time keeping up...
I did a couple events on the stock suspension with just the wheels/tires and it worked okay but the amount of grip was overwhelming the soft shocks and small anti-roll bars. Enter the forums and ebay along with some guys from Charlotte with an SSR C5Z06, and I grabbed some C6Z06 shocks and C5 Z06 rear sway bar and leaf springs. I also ordered Sam Strano's famous 33mm front sway bar to top it off. I wasn't too impressed with the C6Z06 shocks but the front sway bar definitely made a good improvement. I think the stock C5 Z51 FSB is 25.4mm diameter so going to 33mm was a huge change in front roll rate- before the bar the car would take what felt like multiple seconds to take a set in a corner, and after it was much more planted everywhere. Stock bar vs Strano bar:
Better view of how much beefier the Strano bar is:
The big bar really highlighted to me how soft the bushings are in this car though, since now the weight was transferred nearly instantaneously through the bar once you turn the wheel, but then you could feel all the rubber deflecting, and then the car would turn in. Coming from the Solstice with higher ride frequencies, quicker steering rack, and stiffer bushings, the turn-in response of the C5 is disappointing. Most of that can be addressed under ST class rules though so I am not that worried. I also played around with lowering the car around this time, and for one event at zMax I went too far in the rear and even on that smooth surface the car was bottoming out and losing traction abruptly multiple times on the course. Learned my lesson there as I slowed down significantly. Quick tip: aftermarket Corvette websites sell rear lowering kits but you can order 6 or 6.5" long 1/2" Grade 8 bolts and Nylocs from Mcmaster for much cheaper than those lowering kits. Plus you can get bolts with a finer thread pitch for more precise adjustments. A pain when making big changes but could be nice when corner-weighting the car.
6" bolts seem like the right way to go for stock rear spring rates to avoid bottoming out all over the place. I think the photo below is from when I was running it too low in the rear. I had it set at zero rake under static conditions so on throttle it was very low in the rear. It made sense to me that you want the rear low if you are struggling for grip, since there is less weight transfer off the inside tire, but it was too much.
That's good for now. Check back in next time for how the 2014 North Carolina Autocross Championships went.
