STI Killer Improvements - Searching For Seconds, Part 1
The STI Killer goes from track junky to an R&D fixture in our quest for lower lap times and improved grip
From the December, 2011 issue of GM High-Tech Performance
By Justin Cesler
Photography by Steve Baur
It has been a little while since we've had the STI Killer in the pages of GMHTP, but it hasn't been for a lack of effort. Since our last official outing, where we bested a Subaru STI around Gainesville's 1.6-mile road course, we have been working almost day and night on the Killer, attempting to take the build to the next level with help from Baer Brakes, Weld Wheels, Toyo Tires, AntiVenom, and ProFab Performance. While the Killer was already a force to be reckoned with, we've set our sights on some much more expensive and capable cars and chasing them down around a road course requires a little more elbow grease and leg work than previously anticipated. This month, we are going to cover some of the work that we've been up to along with some of the road blocks we've experienced along the way.
If you've been following our series, you may remember the six-piston front brakes we re-appropriated from a Cadillac CTS-V. Built by Brembo for Cadillac, the six-piston front calipers and massive rotors (from a C6 Z06) worked really well on the Camaro, although they did come with some compromises. First, brake bias was off slightly and the Camaro didn't bite quite as hard as we had hoped. Secondly, the rear CTS-V brakes that we ordered wouldn't work with our C-clip rear axle, which we hoped we could solve with a set of brackets. In searching for a solution, we found Baer Brakes, a company you are no doubt familiar with, and the company's brand-new Tracker full-floater conversion system for the 10-bolt rear. Built to eliminate the factory C-clips, replace the axles with a double splined unit, reduce axial loads, and replace the factory two-piston floating calipers with massive four- or six-piston fixed units, we knew we just had to get a set for the Killer. Unfortunately, time was not on our side and Baer's production and R&D schedule pushed the Tracker just outside of our deadlines, leaving us searching for a temporary solution, until the Tracker was ready for installation.
It was at this juncture that we chose to prepare the rear end for the Tracker (or an equivalent solution) anyway, by taking it apart, dropping it off at ProFab Performance, and having Matt LaRue narrow the rear to our specifications. If we were going to have to make changes to the rear in the future and cut on it to install the Tracker system, we figured it would be wise to get all of our measurements now, along with our wheel offsets and sizes, so that we wouldn't have to go backwards in the future. Along with that, we also wanted to test fit a set of six-piston Baer rear calipers, along with the company's VeriSlide rear bracket, to see if we could get away without a full floater conversion and to make sure we had proper wheel clearance and braking power going forward.
Enter Gregory Smith and the crew at Weld Racing. Before we could even think about picking a wheel, Weld was on the case, interested in testing and producing a massive set of 18-inch RT-S S71 wheels for the Killer, which could take all the abuse and lateral loads we could throw at them, while keeping us safe on track and holding a set of sticky R-compound tires in true style. In a departure from the Weld wheels that made the company famous, the RT-S line is built upon a modular three-piece design that features a forged billet center and a cold forged rim shell that exceeds SAE J2530 wheel standards and can support loads commonly found only on the racetrack. Above that, Weld Racing offers three different "pad heights," which allow the spoke to clear even the largest of calipers, including the six-piston Baer 6S and 6P calipers we were planning to install. Technical mumbo jumbo aside, the RT-S S71 simply look fantastic and really set the STI Killer apart from other fourth-gen F-bodies we have built thus far, and that alone made them a must have item!
With wheels and brakes in hand, we needed a set of tires that could stand up to the rigors of repeated 20-minute sessions at Sebring International Raceway, take a beating at an autocross, and handle some street and dyno duty on a regular basis. Unlike a drag race application, we were also looking to stuff large 295mm front tires and massive 315s out back, which could keep us glued to the track in any condition. It didn't take long to find Toyo Tires, the company behind the famous R888 line of R-compound tires, which are "Ideal for road racing, track days and high performance driving schools." Perfect. Anyway, enough with the talk, let's see what all of this stuff can do and make sure you stop back to see what else we have in store for the STI--no--Z06 Killer in the future...
1 Having big, beefy six-piston...
1 Having big, beefy six-piston CTS-V calipers up front made for some exciting deceleration in the Killer, although we left the racetrack feeling like we could upgrade the entire braking system and gain even more of an advantage over our competition while giving us room to grow and add a proper rear brake caliper in the future.
2 Enter the Baer Monoblock...
2 Enter the Baer Monoblock 6S six-piston caliper, which is built from a single piece of forged aluminum for maximum stiffness and minimum weight. While obviously gorgeous, the real magic of the Baer 6S is internal and makes it the perfect caliper for a dual duty street/race car like ours while providing increased pad fitment and consistent deceleration.
3 Besides the front calipers,...
3 Besides the front calipers, Baer also offers two unique rear solutions, including the Tracker full floating conversion (left) and the VeriSlide bracket (right), both of which we were interested in testing for this article...
3b ...Unfortunately, the...
3b ...Unfortunately, the Tracker wasn’t quite ready in time for our install, so we tried the VeriSlide instead, which needed a little tweaking to work properly on our application. More on that in a minute…
4 The stock rear brakes work...
4 The stock rear brakes work well, especially with upgraded pads (like those EBC YellowStuff pads), but they left a lot to be desired in terms of overall performance and looks. Here, Greg Lovell of AntiVenom is removing the caliper and rotor from the STi Killer’s 10-bolt rear.
5 With the caliper and rotor...
5 With the caliper and rotor out of the way, Greg pulled the stock axle out of the rear by removing the rear cover and the C-clips before loosening the four bolts that hold the rear backing plate to the factory axle tube. To install the Tracker, you would have to cut the rear and weld a new axle end in place, while the Baer VeriSlide unit only requires a new backing plate.
6 Once we had the backing...
6 Once we had the backing plate removed, Greg dropped the entire rear out of the car and we hauled the housing down the street to our friends at ProFab Performance. Matt LaRue is a master welder and fabricator and was our first choice for cutting and welding our 10-bolt into a shorter unit.
7 Measure twice, cut once....
7 Measure twice, cut once. Here, Matt is making the second cut into our axle tubes, cutting a 2.25-inch section out of the tubes to pull the rear mounting points inward, effectively narrowing the rear 4.5-inches total, which will both decrease our overall length (obviously) and allow us to run a rear wheel with a lot of dish to give the Killer a new and improved look.
8 Matt likes to bevel the...
8 Matt likes to bevel the end of the tube prior to welding on it, which allows the bead to nicely fill in the bevel, making for a strong and leak free weld. Good, clean metal is also essential to a nice weld and Matt took his time to make it right.
9 Of course, you can’t just...
9 Of course, you can’t just eyeball the angle and weld everything back together. Because the end of the axle tube houses the axle bearing, seal and the backing plate flange, it must be perfectly square to the rest of the rear or else you will have major problems. ProFab has an in-house rear end alignment tool, which slides through the rear and bolts down in the center housing.
10 With the bar in place,...
10 With the bar in place, Matt slid the old housing end in place and aligned it using the tool, his eye and several levels, angle finders and rulers. Remember, this has to be spot on for everything to work correctly, so make sure you find a qualified fabricator to pull it off or take your time measuring and double checking everything before laying down a set of tacks and stitch welds.
11a Instead of the stock...
11a Instead of the stock backing plate, Baer sent us a brand-new backing plate unit, which was equipped with the VeriSlide mechanism...
11b ...The VeriSlide (right)...
11b ...The VeriSlide (right) allows the caliper bracket to move with the rotor and axle, as they slide in and out under load. If you tried to run a fixed caliper with a C-clip axle, you could encounter “pad knockback” an issue where the rotor/axle actually pushes the pads back into the caliper, leading to a soft pedal.
12a A shorter housing also...
12a A shorter housing also means you need shorter axles, and for our project, we ordered a set from Moser, who had them made up and shipped out almost before we got off the phone with the tech department...
12b ...Narrowed 2.25-inches...
12b ...Narrowed 2.25-inches per side and equipped with 28-spline ends, these custom axles were a direct plug and play for our narrowed rear and fit perfectly without any issue.
13 Up front, we removed the...
13 Up front, we removed the CTS-V front brake calipers and installed Baer’s fourth-gen specific bracket and bolted everything down to the spindle. This design allows the 6S caliper to bolt on without any additional modification or cutting, which makes it truly a bolt-on affair.
14 The two-piece slotted...
14 The two-piece slotted Baer rotor drops on next, making sure to install each rotor on the correct side. While the two-piece design is slightly more expensive up front, it becomes cheaper over the life of the car, since replacement rotors are cheaper than replacing the entire unit. Add to that the lighter weight of a two-piece rotor compared to a one-piece and the fact that the disc usually runs cooler and can expand independently of the hat and you have a recipe for success.
15 Time for the crowning...
15 Time for the crowning jewel, the Weld RT-S S71 three-pieced forged aluminum wheel. A true three-piece welded design, the Weld RT-S S71 features a forged billet center and a cold forged rim shell for maximum strength, function, and style. Weld Racing offers these wheels in any size from 15x4.5 to a massive 20x18, although we chose to equip the STi Killer with a set of 18x10 (front) and 18x11-inch rears, with massive lips and pad heights to accommodate large front and rear brakes.
16 We wanted to get pretty...
16 We wanted to get pretty aggressive with the fitment and Weld Racing was on board for anything we could dream up. Here, you can see a massive 18x10-inch front wheel, which features 7.1-inches of backspacing (41mm offset) and a high pad spoke design to easily clear big brakes like the CTS-V six-piston (shown) and the Baer 6S. If you’re running a smaller brake package, you can use a medium or low pad design to sit the spokes up flatter and increase the wheels lip and appearance.
17 Head on, you can see the...
17 Head on, you can see the Weld RT-S tucks perfectly under the stock Camaro front fender and fits flush to the outer edge of the bumper, door, and wheel opening. The import boys would call this “hellaflush,” but we just call it awesome. Remember, a 10-inch-wide wheel is actually 11-inches wide and with a 295-series Toyo R888 up front, this is a lot of meat that will work perfectly with our massive 1-inch BMR front sway bar.
18 Out back, the huge 18x11-inch...
18 Out back, the huge 18x11-inch Weld RT-S fit in perfectly with the 2.25-inch narrowed rear end and show off the Baer 6P rear caliper and massive two-piece rear rotor. To say Weld did an incredible job with this wheel design would be a massive understatement, it is just perfect for the Killer and its overall attitude, demeanor, and race styling.
19 The payoff for our narrowed...
19 The payoff for our narrowed rear is tucking a set of 315/30/18 Toyo R888 tires and mounting them to a wheel with a serious amount of rear dish and lateral stability. If you’re interested in this exact setup for your car, you know who to call and they can get you going with no problems. Just be aware, you’re going to have to answer a lot of questions everywhere you go, but we think it is worthwhile!
20 Excuse the dew and dirt;...
20 Excuse the dew and dirt; we took this photo first thing in the morning after an all-nighter to get the car to Sebring International Raceway, which you can read about elsewhere in this issue. With the full Baer Brakes six-piston setup stuffed with Hawk DTC-70 pads, Weld Racing RT-S wheels wrapped in Toyo tires, and a newly narrowed rear, the Killer was ready for a full day of racing.
21 After two full days on...
21 After two full days on track, we brought the Killer home to tear everything down to see how everything looked. Unfortunately, as part of the R&D process, the left rear VeriSlide backing plate and 6P caliper suffered some damage, an issue that we are currently investigating with Baer (better us than you, right?). It didn’t keep us from racing, but we needed to tweak the combination a little further to get things perfect...
22 Which meant we dropped...
22 Which meant we dropped the stock brakes back on the rear for our trip to Gainesville Raceway, allowing us to further test the new wheel and tire combination, along with the braking ability of the front 6S caliper. While not the optimal setup, we did see a 1.5-second reduction in lap times (1.05.2 vs. 1.06.7), which proved that all of the effort was worthwhile.
23 With the Baer six-piston...
23 With the Baer six-piston brakes up front and the stock rears, we still experienced some bias issues, which we hope to figure out in the future. Unfortunately, this type of issue is just something that happens when developing a car and has to be taken into consideration with each new modification. We attempted a series of brake tests to see how the new front binders performed in an all out 60-to-0 test, but ABS problems kept us from getting any useful data...for now!
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