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Unread 01-09-2015, 11:45 AM
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Default Re: Vorshlag Budget TT Build: Project DANGER ZONE

Project Update for January 9th, 2015: The first stage of "initial race prep" for this project is getting down to the wire with the NASA race debut only ONE week away! Let's get caught up on the work we've been knocking on Project DANGER ZONE, our TTC class prepped 1992 Corvette. I had intended this to be a quick update, showing the initial stages of race prep, but I started writing and somehow this post spiraled out of control. It now includes some aero/drag reduction theory, the History of Iron and Steel, a good bit on roll cage tubing and design, some tire analysis, and other random tidbits of tech. If you get bored easily just skip down to the pictures and enjoy.

Safety First, Kids!

There are many Safety Upgrades we want to add to (or repair on) this Corvette during the 2015 season, which are the same for virtually any dedicated road race build. Unfortunately we were pressed for time and won't get them all done before the first race. The Safety list includes: a full roll cage, racing seat install, 6-point racing harness, window nets, full fire extinguisher system, secondary 2.5 pound fire bottle, tow hooks at both ends, tie-down hooks at both ends (for towing), replace the broken windshield, replace the rear hatch glass with Lexan or Plexiglass, and more. That's a lot of parts and work on the "Punch List", but as far as what's "required" for NASA Time Trial, that is much less. We also have some repairs and performance upgrades to tackle, too. We got almost nothing done over the holidays (short weeks, busy on customer cars) so let's see what we can get done in two weeks.

Windshield + Small Aero Improvements

This repair is really a safety upgrade, because you cannot race with a busted windshield. Before I bought the car from Matteucci he had warned me about this problem - it had a lot of big cracks on the passenger side and chunk missing where the OEM rear view mirror attached, with the cracks propagating into the driver's view. The upper right corner of the windshield trim and weatherstrip took a hit when a former owner (ie: The Crackhead) drove it through a barbed wire fence. Matteucci literally found a crack pipe (maybe a meth pipe) in the car after he bought it. So yea, now you understand part of why this was a $3000 running and driving car purchase.

Nasty, broken windshield and trashed weatherstripping has to be replaced

We discussed delaying the windshield replacement because when you install a roll cage it is ALWAYS easier (and often required) to get the front windshield out of the way to access and weld tubes along the front of the cage. In some cars with a fixed rear glass window, that is often removed as well. The cages we built in the two cars below required the windshield to be out. At left is an SCTA legal cage for 200+ mph use on the salt flats, which has more of a "Funny Car" drag racing cage (built per the rules). To weld in the the front tubing gussets requires windshield access. The one at right is a NASA ST3 legal Mustang the the dimple-die gussets and front corner tubes need windshield access - as does a proper paint job on any cage.

We knew we wanted a roll cage in DANGER ZONE (to reduce the "zone of danger"), but with only 2 weeks of time build available after the short holiday weeks between Christmas and New years, and many other items that needed attention, meant only building a 4-point roll bar for this first race. Which meant the windshield didn't need to come out. But it was so cracked that it would never pass tech, so it had to be replaced. And when we go back and finish the full cage, out it will come again!

We called our buddies at Titan Auto Glass and they extracted the old and busted and installed the new hotness. There are normally several windshield choices for most cars, varying in price, but for 24 year old Corvettes there was one - and it was a tick pricy at $260 installed. But hey, can't race with a busted windshield. Going to Lexan is an option but there are more downsides (more costly, harder to install, easily scratched, difficult to use wipers with them, more easily nicked by rocks or tire klag) than upsides (slight weight savings). A two layer, laminated, glass OEM style windshield is preferred by many racers when they have a choice.

The OEM windshield surround rubber weather stripping was a total mess (above right). Matteucci had cut away the bits around the A-pillars when he gutted the interior and the top bit was destroyed by the barbed wire. The crackhead former owner had filled in the missing chunk in the rubber seal with SHOE GOO, and that had to be chiseled away (thanks Titan!).

I wasn't about to put this mangled mess of rubber seals back on, but we needed the top bit of rubber to seal the targa roof panel smoothly along the top of the windshield and I also wanted the seals back in place along the edge of the windshield at the A-pillar. This should help smooth the airflow in a high payoff "Green Zone" of potential drag reduction - the edges of the windshield. Read this NASA Speed News article called "Getting Into The Zones" (page 60) written by aero guru Neil Roberts (also read his ThinkFAST Engineering blog for more great articles!) and that will make more sense.

A smooth, new set of weather stripping should help aid the transition from the edge of the windshield (sides and top), reducing drag. We are looking to reduce drag in ALL of the Green areas (again, read Neil's article) on this car, and do so legally. We cannot run NASA events with the windows up, so the door window openings have to stay. We have tried to read the rules to say otherwise, but rule 7.2 of the NASA TT rules is pretty clear:

7.2 Front driver and passenger side fixed/Lexan windows are specifically not permitted unless they are factory installed during the manufacturing of the vehicle. Both front side windows must otherwise be in the down position while on track."

Running the windows UP would be a decrease in drag but it is not allowed in virtually any form of road racing, for safety reasons (easier extraction after a crash). Some drag racing classes and high speed events like Bonneville do allow for side windows, so the silver Subaru we're building the cage for above is getting a full Lexan window package (4 side windows + front and rear windscreens).

Why Terry Needs A Roll Cage

There isn't any additional safety requirements in NASA Time Trial groups than what is called for in HPDE run groups: a Snell SA2010 rated helmet and OEM seat belt, plus a roll bar for convertibles. There isn't supposed to be wheel to wheel contact in TT, but we are running for times and competing for contingency prizes, and many TT racers take it pretty seriously. I won six sets of Hoosier race tires racing in NASA TT3 class in 2014, and these were BIG tires that cost $1710 a set, so there is some decent swag on the line. When you are chasing a TT win you often push the limits and do stupid stuff...

Crap like this

My personal safety record, for the amount of laps I've driven on track, was pretty damned good up until 2014. In 27 years of running on road courses I only had a couple of "offs" that were worth mentioning. I de-beaded a couple of tires in a high speed off at TWS in the late 1980s that curled my hair a bit. A number of times I've had a quick "off and on" that bent a splitter or packed a grill with grass, sure. The stock brake pads came apart and I left Turn 7 at ECR at 90+ mph in 2013 in a stock '13 Mustang. But by far my most memorable off-track experience happened in 2014 (shown above).

After the crash I began wearing a HANS device and fire suit to complement the FIA halo seat, 6-poiont harnesses and roll bar in our TT3 Mustang

I briefly mentioned this in my first post, but it was a pretty spooky incident and I figured it might explain my "overkill" safety requirements for this TT build. After losing brakes at at Road Atlanta at a Global Time Attack event in May 2014, I went off the end of Turn 10A at 150mph, through the gravel trap, and took a big vertical hit coming out of a trap. I got hurt but the car barely took a scratch (splitter came off, was repaired and reinstalled and back on track 2 weeks later, but not with me driving). Even though I had a proper FIA halo seat, good harnesses, and a good roll bar, I wasn't wearing a HANS device. We think this might be why I fractured a vertebrae in my back and broke a rib. After this incident I was in a lot of pain, wearing a back brace for 2 months, and not racing.

Having gone through the crash scenario many times and analyzing frame-by-frame pictures of the crash since, the injury seems to come down to too much "arching" of my back in the impact that broke these bones. A properly worn HANS device would have likely prevented this injury. The "off" happened because I ran out of brake pads, and had been ignoring measured brake caliper temp data of 490°F+ for months. I'm not going to make those series of mistakes again, and I also vowed in 2014 to start racing with better personal safety gear. I was setting a bad example and I needed to do better.

So obviously, after this back-breaking scare I'm taking my safety on track a lot more seriously. I've starting using a HANS device (still haven't picked my favorite model after trying 4 different brands - and I'm about to try the brand new Schroth HANS design, since we are a dealer) and an FIA 3-layer driving suit in all TT events. I am also wearing my harnesses TIGHTER and keeping a much closer eye on things like brake fluid temps and brake pad material depth, so this scenario of failures never happens again.

Roll Cage Is Safety More Than Performance

The steel frame structure of the C4 Corvette. This is a 1984 model

After the personal safety gear, the next most important safety aspect of any race car is the roll cage. This structure is helpful to make the chassis more rigid, sure, but it is there mostly to prevent bodily injury in many types of crashes and "offs". These include single car off track frontal collisions with a barrier (somewhat common), a roll-over crash (very rare), or any car-to-car contact (more common). While a roll cage wouldn't have helped me in my gravel trap "jump" incident at all, there are other types of crashes where it could save your life - and do so more effectively than the basic 4-point roll bars we have used in my last 3 personal race car builds. I own a shop that builds roll cages and haven't had one in my own cars in 6 years... that's crazy.

Corvette roll cages are tricky. All Corvette chassis generations (C1-C7) have a strong metal frame (steel frames through the C5, with aluminum frames for C6 Z06 and all C7s) with a composite body attached to it. Adding a roll cage to these cars has some extra challenges, since you need to cut away fiberglass to access the metal frames, but its nothing we haven't done before.

As I spoke about above, TIME is not on our side for this first NASA event, so we had to cut back on the roll cage plans for the maiden voyage. We could have bought a second-hand 4-point roll bar but it would never fit as tight to the roof structure in this gutted car (they are usually made for full interior cars).

Frame differences on the 1984-1991 (left) and 1992-1996 (right) C4 Corvettes

Quick sidebar: the C4 Corvette had major changes to the suspension (1989) and even to the frame (1992), along with major changes to the drivetrain (1989 for ZF and 1992 for LT1), front crossmember, and transmission tunnel over the 13 year long model run. The two "body shop spec" images above show the changes to the frame at the 1992 model year, and we've noticed a lot of other differences to the interior fiberglass structure.

Last year we caged and safety prepped a 1987 Corvette convertible (shown above) and after looking at pictures of both that and our 1992, it had a lot of structural differences at the tunnel, firewall, and rear bulkhead (behind the front seats), not to mention the dash, body, and other obvious differences. The frame was also different in some key areas. We are using the NASA CCR for cage design specifications on our car, but the black 87 used a mix of NASA, WRL, Lemons and ChumpCar series cage rules.

A Brief History of Iron and Steel

OK, this is a big tangent. It might not be boring to a racer - unless you are a metallurgical engineer. Modern race car roll cages are made from steel tubing (aluminum is not allowed) and picking the right alloy and type of tubing for the job involves both a rule book (General Competition Rules or GCR/CCR) and some engineering knowledge. There are generally TWO accepted types of tubing allowed for roll cages in SCCA and NASA: 4130 Alloy steel and 1018/1020 Low Carbon (aka: Mild steel) Steel DOM tubing.

Working as a Mechanical Engineer at a foundry in my first job out of college exposed me to a lot of practical metallurgical design and lots of different steel alloys. I also took a welding class at college, where we talked a lot about steel and iron and the changes welding can do to metal's molecular structures. That's where I learned that steel is the best metal on planet earth, and in many ways unique among all metals.

Iron is is, by mass, the most common element on Earth, forming much of Earth's outer and inner core (same scenario in almost any rocky planet). It is also the fourth most common element in the Earth's crust, which means it is relatively easy for humans to get at and mine. The production of iron by humans began sometime around 2000 BC and was so significant it began what is now called the Iron Age - when iron replaced bronze in implements and weapons. This shift occurred because iron, when alloyed with a bit of carbon, is harder, more durable, and holds a sharper edge than bronze. For nearly four thousand years, until replaced by steel after ~1870, iron formed the material basis of human civilization in Europe, Asia, and Africa. Iron has shaped human history for the past four thousand years, and it's use accelerated technological growth.

Natural "iron ore" has a lot of oxygen in it, so it is smelted at high temperatures to extract a more pure mass of iron. Carbon naturally gets mixed in at these high temperatures (along with 2-3 other elements) which means cast iron has a relatively high proportion of carbon (3-4.5%). This makes cast iron hard and brittle; it is liable to crack or shatter under a heavy blow, and it cannot be forged.

Blacksmiths learned to work iron - after heating it in a furnace at high temps they removed a pasty mass and hammered it on an anvil to drive out the cinders and slag and to compact the metallic particles. This Wrought iron (“wrought” means “worked” or hammered) contained generally from 0.02 to 0.08% percent of carbon (absorbed from the charcoal), just enough to make the metal both tough and malleable. Wrought iron was the most commonly produced metal through most of the Iron Age.

Steel alloys have a little bit of carbon in them (0.2 to 1.5%), enough to make them harder than wrought iron, but not so much as to make it as brittle as cast iron.

continued below

Last edited by Fair!; 01-09-2015 at 03:33 PM.
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