Subaru BRZ Scion FR-S Autocross SOLOII SCCA WAI MIlwaukee Region Bart Hocerman Wes Dumalski Feal Whiteline Enkei Dunlop Kartboy Ballistic
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MotoIQ Autocross BRZ SCCA SOLO II Milwaukee Region Bart Hockerman Wes Dumalski

Project Autocross BRZ: Part 1 - Building a Better Cone Dodger

by Wes Dumalski 

Let’s face it, autocross is hugely popular. There is a statistic floating around that the SCCA Solo II Nationals is the largest motorsport event in North America. While I have not audited that fact, I can tell you that a LOT of people love the sport. In fact, my very first interest in automotive performance was an autocross event that I attended and competed in after being encouraged by a friend to give it a try. After that event out came the stereo and in went suspension modifications. That car was Project 200SX and the year was 1999. I have always had a penchant for the sport but after spending more time at the road course, life sideswiped me and my participation in AutoX events waned; that is, until recently.

After the Subaru BRZ and Scion FR-S were introduced, they became immediately popular on the autocross circuit and for good reason. With their balance, braking, and neutral handling, the theory was that they would be very competitive in several different autocross classes. It was time to bring autocross to MotoIQ and it was time to build a BRZ for SCCA Solo II competition. Our car is a 2013 Subaru BRZ premium in World Rally Blue and honestly, it is the first time I felt like I LIKED the WRB color! With the car chosen, we had to decide on what class to run and immediately begin to prepare the car to the maximum extent of the ruleset. With the car being a joint effort between myself and its owner, Bart Hockerman, there was no time to rest and start racing the car in stock form. Bart is a serious competitor within the sport and in order for the car to be competitive at local and national level events changes needed to be made and FAST! While we will move quickly with putting parts on the car, this series will also cover more subtle changes in setup as we do more events with the car and learn to better exploit the car's potential. 

 

Project Autocross BRZ Sommers Subaru WRB World Rally Blue

The car looked like this for less than 2 weeks! If you want to be competitive when autocrossing on a local (let alone a national) level, a stock car won't cut it. Besides, I never cared for the OEM wheels or overall stance. Oh and thankfully our car does not have the OEM rear spoiler!

The FIRST step was to closely review the ruleset for our chosen Street Touring Extreme (herein after referred to as STX) class. In a nutshell, this is a class designed to showcase a vehicle's mildly modified performance. Tires are limited to DOT rated legitimate Street tires with a minimum tread wear rating of 140 UTQG, wheels are able to be changed, suspension is fairly open but limited to using the factory mounting points, and there are some regulations regarding damper amount of adjustability. Power adders are limited to bolt on’s, catalytic converters must be retained and cannot be relocated more than 6” from the rear-most OEM cat placement. A bolt on street car is essentially what this class is designed around. For this reason, it is very appealing to many people as it makes for close competition, as well as being easier on the pocketbook than some of the more extreme classes. Make no mistake, serious thought and effort is put in to sorting out the best of the best within this class. However, the cost of entry is much less than many other classes and the amount of fun to be had is EPIC. If you are super curious as to the ruleset specifics you can find them here. 

Before we even took delivery of the car we had reached out to our good friends at Kartboy. Having used their parts with great success on our Gen 3 STi project, we knew we would want to see what they had to offer for the BRZ. They were the some of the first people to release a short shifter and they did a fantastic job with this part. The OEM shifter is nicely placed and not horrible by any stretch; however reduced throws, a shorter shifter position, and a tighter feel is always welcomed (did I just say that?). The Kartboy shifter is a complete replacement piece that reduces throws by 28.5% and is made right here in the USA, each one hand welded on the same jig. The kit also includes the proper parts for the reverse lockout mechanism. What we liked most about the shifter swap is that it can be performed completely from the inside of the car! No need to jack up the car and remove the exhaust or other baloney. Just sit inside enjoying your milk and cookies and watch Bart install the thing... err... I mean the install is very straightforward.

Kartboy Short Shifter Subaru BRZ Scion FR-S
 
The Kartboy SS in all of it's installed glory. Bart installed this thing so quickly I only had time to consume 2 beers (um, milks). Also notice the necessary reverse lockout bracket that is included with the kit. 

The shifter and transmission bushings from Kartboy also serve to tighten up shifter feel and afterwords everything was very crisp and direct. We maintain that by reducing the shifter throw we will have a competitive advantage over other cars in our class who take longer to shift... OK that is total nonsense but I am sure you could overhear that type of banter in the grid at an autocross event- they really are that serious about their car prep.

Kartboy Subaru BRZ Scion FR-S Trans Bushing
 
The Kartboy Transmission Bushing fills the void in the center with 85A Durometer urethane. It's like Viagra for your tranny... Wait... err... 
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Comments
stoves
stoveslink
Thursday, December 05, 2013 8:50 AM
Why so soft on the springs? A rate of 7K is only ~390lbs. FWIW, I had 525lb F/325lb R springs on my STR Miata with no rear sway bar and found the springs to be softer than I'd like (Moving to 700 F/450 R since this seems to be a winning miata setup).

I'm just speculating, but I know nothing about suspension tuning for the BRZ/FR-S.
Wes Dumalski
Wes Dumalskilink
Thursday, December 05, 2013 10:08 AM
Stoves,
We chose to run those springs as a baseline and so far are happy with the results. We did point out in the article that my preference is that for autocross where lot surface conditions can vary greatly we find it beneficial to not overspring the car and to use larger sway's for motion control.
stoves
stoveslink
Thursday, December 05, 2013 10:25 AM
I understand the reasoning better now. Miata wisdom for autox is to ditch the rear bar completely because it limits droop travel and makes it more difficult to put power down on corner exit in a car with an open diff. I'm not really sure if this reasoning applies for all cars and suspension types though.

Both of the lots I run on regionally are similar in surface so I should be alright once I find the right spring rate. I'll probably end up with 2-3 sets of springs by the time it's all over.

Good luck in the coming season, Wes.

Dusty Duster
Dusty Dusterlink
Thursday, December 05, 2013 12:06 PM
Great choice on tires. The ZIIs are great for lighter vehicles like the FRZ-BRS.
M-P
M-Plink
Thursday, December 05, 2013 12:22 PM
Also great choice of wheels. It is VERY hard to beat the RPF1 for weight, strength, and looks when you are trying to get the most bang for your buck.
Mike Kojima
Mike Kojimalink
Thursday, December 05, 2013 1:15 PM
stoves,

The Miata has a much higher motion ratio than the FR-S in the front so the actual wheel rates are more comparable.
spdracerut
spdracerutlink
Thursday, December 05, 2013 2:36 PM
@Stoves, after a quick internet search, it appears the stock spring rates are only 2.8k front, 3.2k rear. Based on my general observation, 2-2.5x the stock spring rate of a standard performance car seems to be a good range to target for a track car running on the best street tires. So the new spring rates are right around this range.
turtl631
turtl631link
Thursday, December 05, 2013 4:00 PM
Car looks good. Will be interesting to follow along with a focused build. Is the stock powerband a pain with that midrange dip?

I will be moving to MKE next summer, not a big autocrosser (more DE stuff) but it will be fun to get involved and meet some driving/building enthusiasts.
2superblus
2superbluslink
Thursday, December 05, 2013 5:28 PM
@turtl631 If you are into DE stuff hit me up when you get into Milwaukee I can introduce you to the local SCCA folks who organize them.

As for the dip in the powerband, it really isn't quite as horrible during autocross although a tune and some free flow in the exhaust system does help to severely lessen the dip.
nissannx
nissannxlink
Thursday, December 05, 2013 7:55 PM
Great article, Wes. Glad to see what you're doing.
stoves
stoveslink
Friday, December 06, 2013 8:10 AM
@Mike Kojima - I hadn't even thought of that Mike. That makes perfect sense looking at it again.
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