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Unread 12-29-2012, 07:10 PM
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Default Re: Vorshlag BRZ Project Build Thread

Project Update for December 28th, 2012: Well, we made it past the Mayan Apocalypse so I guess I can finally post up the work we've been up to for the past three months on various Subaru BRZ and Scion FR-S cars. We have done a bit with Matt's BRZ, drove it at two track days, installed various Whiteline parts and springs into multiple FT86s, and more. I worked on this update for two solid days, so it got pretty long. Let's get started.

BRZ Baseline Dyno Testing

Vorshlag isn't a "engine tuner" shop in any shape or fashion - we don't own a chassis dyno and likely never will. The only things we do to add horsepower are custom fabricated exhaust systems and LS1 V8 swaps, but we don't do any on-site engine building or tuning. So to do any power testing, we have to go to a few local shops that have chassis dynos. Back in mid-October, we took three of our shop cars to a local speed shop we use for tuning our Mustangs (True Street Motorsports) and got 2-3 baseline chassis dyno pulls on each. The BRZ was one of these cars, as was our brand new and bone stock 2013 GT (378 whp) and our headers/cold air equipped 2011 GT (424 whp).



Not only do we have dyno pulls done on our cars to see baseline stock numbers we are starting with, we do it after each power upgrade to verify results as well as sort of "regular engine health check-up". Kind of like an annual physical at your doctor, an annual dyno pull is a good test to make sure all systems are performing how they should. If you see big changes from the same tune/set of parts, it is worth investigating. You do this not only by looking at the peak dyno numbers but also checking the shape of the torque and hp curves (looking for irregular humps, drops or spikes) and also checking the air:fuel ratio (any decent shop that has a dyno will have a wide band O2 sensor reading as well).

Everything looked fine on all three cars and the baseline numbers on the BRZ were right about what we figured they would be. We have one dyno chart showing all 3 cars, and you can see the BRZ plot way down at the bottom. Hey, it is not a horsepower killer!



So there it is - the 167 whp BRZ monster dyno pull. This will be the baseline for hopefully some power improvements. Looking at the shape of the curve told us how the motor pulled through the rev range, with most of the power concentrated from 5000-7000 rpm. With the 6-spd gearbox, the ratios are pretty tight, which meant we knew that shifting at 7000 rpm was probably best, as the power fell off a cliff above 7K. When I was at a track day instructing with someone in an FT86 recently, who was shifting every gear on every lap at the 7500 rpm redline, you could feel the engine power falling off hard at the higher revs. I told him about the shape of the dyno curve above and asked him to shift at 7000 rpm instead. Lap times immediately dropped a full second and engine wear went down considerably (friction goes up with RPM nearly exponentially). Knowledge is power... in this case, literally.

From research done by looking at results from tuner shops, most bolt-on mods that add power to other cars are not showing significant gains on these FT86 cars. We have seen beautifully made, custom mandrel bent exhausts lose power on an FT86. Cold air kits that make the engines run poorly. It all boils down to the ability to add a custom tune - which is proving elusive to the various tuner shops, for now. Once the Toyota/Subaru engine management code is cracked, there could be potential gains to be had. For now we recommend concentrating on handling - tires, brakes and suspension - where we have seen SIGNIFICANT improvements with the right choice of parts.

Wheel & Tire Improvements - EVEN BIGGER!

Obviously we have been big supporters of ditching the factory FT86 17x7" wheel and 215mm all-weather Prius tires. The stock rubber is so very, very bad for performance, the OEM wheels are somewhat heavy, and all of it is too narrow for this 71" wide car (that is WIDE!). We've been preaching the evils of the factory rubber since before the car came out, and I got a lot of flak for the negative review of these skinny stock tires. But we didn't back down, and our theories proved correct - these cars respond immediately to wider tire and wheel upgrades with big grip increases.



A decent wheel and tire upgrade makes huge, HUGE gains in lateral grip on this chassis. Early on we went to a light-ish 17x9" alloy wheel on Matt's BRZ and have used two different performance street tires on them now. First was the 245/40/17 Michelin Pilot Super Sports on the 17x9" wheels, shown below. These tires fit these ET42 offset 17x9" wheels with just a little extra camber up front. No fender rolling or spacers were needed. Excellent street tire, quiet and grippy, and could even double as a good autocross or track tire.


Left: The 245/40/17 Michelin on the 17x9" wheel dwarfs the stock 215mm tire on the 17x7" wheel. Right: 245s installed.

Before his first track event, Matt decided to upgrade to some more track proven EPS (Extreme Performance Summer) tires, the Hankook R-S3, in a slightly wider 255/40/17 size. We ordered these through our TireRack account, then mounted and balanced them here at Vorshlag on the same wheels.



These 255 tires are big and actually fit the 17x9" wheels a bit better, but proved tricky fitting on the front of the car. The 10mm wider tire was touching the lower spring perch, with the large diameter OEM style springs. Just touching, but that's enough to necessitate a spacer.



We had to slip in a 5mm spacer up front to clear the strut, but o make that work we had to add longer wheel studs to the front hubs. You can read about that process below (luckily we stock and sell 65mm press in Subaru studs!). Ain't it fun modding cars? Sometimes it can snowball... one change (tires) can sometimes involve two more (spacers and wheel studs), but the results can sometimes be worth it (crazy grip!). The 5mm spacer proved to be the perfect amount of tire to strut clearance needed up front, with no rubbing on the strut or front fenders (with additional negative camber). The rear bolted on with no adjustments - we could easily get a 9.5" if not a 10" wide wheel out back (but why?).

Notice how we did NOT go to 18" wheels on the BRZ for his track tire? This was no accident. The FT86 chassis is light and nimble, and the stock brake rotors are relatively small in diameter. The only performance reason to increase wheel diameter is to clear larger rotor sizes, period. Everything else is done for STYLE. Big ballin' wheels look cool and cool cars are fast - or that's at least what we've been taught. If you can turn off that instinct and go with what is actually better for handling, you will stay with 17" wheels on these cars. As you can see below, even with +30mm more tire width (that is huge!) and +1" of wheel width, the 17x9" combo is very similar in weight to the 18x8" combo shown (and this 17" wheel isn't particularly light).


Compare the weights of a somewhat heavy 18x8" wheel and 225mm tire to a light-ish 17x9" wheel and 255mm tire.

Technically the FT86 could even use 16" wheels and still clear the stock brakes with ease, but then your tire choices shrink to almost nothing. This stems from a problem of tire size availability in smaller diameters. The tire manufacturers have catered their offerings to the car manufacturers' ever larger wheel diameter fascination, and now to get any decent widths in performance tires you have to go to 17". Well 17" diameter tires tend to top out at 255mm (some 17" tires go to 265mm) width, so if you want wider you have to go up to 18". Each step up in wheel diameter shortens the sidewall height (bad for ride and handling), ups the weight (bad), and ups the cost (bad). It just becomes a whole big bag of bad, so if you are chasing ever wider tires you end up in 18" wheels - but on big heavy cars you have to do that. We feel that the 255mm tire fits the lighter weight and overall performance of this car very nicely, so 17" wheels will work the best. For a street-only "fun" set of wheels... sure, go crazy 18", but just know that it will be heavier, ride worse, and tires will cost more than a similar 17" wheel set-up would.


This BRZ on the 17x9" wheels and 255/40/17 R-S3 Hankook tires is 71" wide, and the big track width is great.

Better Brakes for the BRZ?

Matt's car has also had some brake system upgrades to get it ready for the track. We left the rotors and calipers alone, because we wanted to see how well the car could do on track with just upgraded pads, lines and fluid. And the results are that it does VERY well with those upgrades alone. Incredible braking performance, no noticeable fade, and no need for more brake torque. So a "Big Brake Kit" (BBK) upgrade is not on the short list for mods, or even the long term wish list, until the car gains a lot more horsepower.



We took a gamble and went with a pad brand that several racers recommended - Carbotech. The XP12 compound were used up front and XP8 in the rear. This seemed like the best "track pad" for the size brakes the car had, according to Carbotech. And they were right - it was spot on perfect. They did recommend the XP10 compound for the front as well, but it wasn't available in time for the first event. Sure, they dust and make lots of noise, but we didn't want a compromised dual-purpose pad. These are used for track events only and after tracking with them twice, we think they were the right choice (and they still look great!). We swap back to the OEM pads and rotors for street and autocross use, which are quiet, work better cold and make a lot less dust.



While the pads were going in, we had custom stainless braided Teflon lined brake flex lines built to order. These are made by a friend of ours using high quality BrakeQuip brand parts, and all ends are crimped on a DOT numbered machine, for the best possible quality and street legality. We made them exactly like the OEM brake lines, with all of the goofy Subaru style banjos and FT86 specific ends and brackets, unlike the lower cost brake line kits we've seen popping up for the "FT86" chassis. Most of those are somewhat generic Subaru WRX kits, with many of the brackets missing and none of the locating tabs.



This makes our Vorshlag FT86 brake line kit cost nearly fifty or more dollars than the other braided brake hose kits out there, but our lines actually fit the FT86 exactly like the original Subaru lines. The lines attach to the struts just like the stock ones, and aren't held in place with a zip-tie. The ends are clocked properly and point in the right directions, for a kink-free installation. Our motto is Do It Right The First Time. The details are too numerous to go over here - check out the product page linked here to see the differences in our lines vs cheaper ones. Our kit will never be the cheapest out there, not by a long shot. Making the lines to fit and function exactly like stock lines is harder and costs more. These are DOT approved stainless braided lines, so they don't have the expansion/flex of the stock rubber lines. Better brake feel and the utmost in safety.

We also flushed the old factory brake fluid out and went with a full bleed using Motul RBF600. The much higher boiling point of the Motul brake fluid means less chance of boiling on track and going all to mush. We didn't do this on my 2013 GT for the October NASA event and I lost the pedal about halfway through my first sessions and drove right off the track! Huge mistake - never skimp on proper brake fluid for any car you take on track. At the bare minimum the brake fluid should be replaced with high quality, high boiling point DOT4 fluid.

Does the car need brake ducting? Surprisingly it didn't. After I took several hot laps in the car, abusing the brakes like I tend to do, Matt's BRZ with these pads/lines/fluid made lap after lap topping 1.4-1.5g under braking. Hey, at least that's what the AIM Solo data shows, and we were out-braking all sorts of cars. I was amazed that I couldn't overheat the brakes, but maybe I could on a hot Texas day taking a full 20 minute session of abuse. I could overheat the 255mm tires before the brakes would fade, so who knows? If we see the brakes fading with more suspension mods and lower lap times, we will come back and look at adding brake ducting to the front. But for now it seemed fine without it - a rare thing in modern sports cars.

(continued below)

Last edited by Fair!; 01-02-2013 at 08:08 PM.
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