3.6L Boxster GT Racer
 

Been sharing a bit of my GT class Boxster build over the last few months. After a year and a half in the BSR I decided to make a jump to GT class power/weight racing. Considered selling the BSR and trying to get a cup or build a 911 car, but the Boxster platform has been so much fun to drive.

Sold off the motor, 5 speed transmissions, Pss9's, all the wheels and started to buy parts for the upgrade.

Basic parts I collected for the project:
Got a 3.6L M96 motor that had an IMS failure at 49k miles.
Picked up a G86.20 Boxster S 6-speed trans that was built for a GA car with steel synchs and short 3-6 gears.
Got a set of 4 front Sachs double adjust cup shocks.
Also acquired a Pectel ECU and Motec CDL dash.

Last day on track as a BSR

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Ready to come apart

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Some of the goods

failed ims shaft 3.6L M96 motor
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Rebuilt the motor with some new Carillo rods, fresh rings, a repaired IMS shaft and L&N bearing, slight clean-up on the heads, fresh valve job, removed the P/S pump, all secondary air injection, removed the A/C and heater, installed an under drive pulley, flipped the intake, installed the "motorsports" air/oil separator and a few other little things.

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Expecting to get 315-330rwhp out of the car with 91 octane, a bit more on race gas. Will likely limit the car in the 305-315 range to keep the car weight down between 2750-2850lbs. When running the car uncorked, it could potentially be at 345 and 2650.

The box has had steel synchs and the Albins short 3-6 gears installed. I added a G50 diff with GT parts and changed out the stub axels. Also added a transmission cooler provisions to use my existing system. To use the 6-speed box in an early Boxster, I had to get some new trans mounts, some Boxster S rear uprights, and some Boxster S axles.

gear chart - http://californiamotorsports.net/996%20Boxster%20S%20986%20short%203rd-6th%20gears.pdf



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In between the two will be a new AASCO flywheel and Tilton 7.25" twin disc metallic clutch unit.

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For suspension duties, I chose 4 996 GT3 cup fronts in the form of Sachs double adjusts. These can typically be had from old team spares or take-offs from people upgrading their cup cars. They are going to be quite a step up from my old Pss9's and not break the bank.

Quite a bit of modification needed to be made to the shock bodies intended for the rear of the car. The piggyback reservoir had to be moved down on the body and we added some threads further down the shaft. This will help us get the desired ride height and droop travel needed. All four were just rebuilt after the modifications. They will control the Eibach main and tender springs. Spring rates are going to need some testing.
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In the front, I'm also going to be using 996 cup uprights. The 996TT/997S calipers bolt right up. I can use a 997S rotor with a little bit of spacing adjustment.

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Also removed all of the GT3 "street" control arms with the rubber bushings and replaced them with the RSS pieces. Also used their height adjustable rear toe arms.

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to keep up with some of the big boys, the Boxster is going to need some proper rubber. We have a great tire contingency program with Yokohama available with free slicks available. That was actually one of the deciding factors on converting the car for GT racing initially. To be competitive, I figure I will need either 240 or 250 fronts and 280 rears. Fitting these under stock Boxster steel is quite difficult.

I ended up getting myself two set of 18x9 and 18x10.5 wheels from Jongbloed. They were real quick and easy to work with. I had them all hard anodized and I think they look pretty sharp on the car. I mounted up some used 240/280's for fitment and found out there was a need for some bodywork.

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off to the body shop...

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now ready for some flairs

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Evan has ben spending some time working these used 996 flairs into something usable on a Boxster. I think they are coming along pretty nicely, but still a little ways to go. Eventually he'll create some molds off of these so we can duplicate fresh ones in the future.

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Also got the front brakes together. The new cup uprights had a wider caliper bolt spacing. Outfitted them with 996tt/997s calipers and some Pagids. The fitment required making some shims for the rotor to center in the caliper.

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Removed the power brakes and ready for dual masters.

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We put together an exhaust quickly for the 92 db limit at Laguna Seca next weekend. We used a total of four Flowmasters hushpower mufflers.

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Then handed the car over to Neel at APEX for some of his tuning magic on the Pectel ECU. We ran it on race fuel and power kept creeping up along with timing advance. We ran out of fuel with the stock injectors and had to move up to the 3.8L 997S units. Then the power really kept coming until we called it good at 335rwhp. The plan was to restrict down to about 310 and that was done using the drive by wire throttle. It actually closes to about 60% throttle to keep the power down in the higher RPM's. So we have a great GT racing motor with 300+rwhp through the entire shift range and it is tuned very conservatively.

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electric power steering is ready to go. Dual master cylinders are in and ready to go.
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MK1 GT3 bumper got painted, stainless screens, and an MK2 cup spoiler.

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finished tidying up our custom wiring harness.

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Then I could finish up installing the rest of the interior. Starting to look like the old cockpit I remember!

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ready for some suspension set-up now!
Just need to finish up on the rear wing, install the lexan windshield, change the oil, and give everything one last look before we head out to the track for the weekend.

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Evan finished up the wing mounting today, 996RSR size.

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Car debut was this past weekend at Lagune Seca with POC.

First practice, we wanted to see if we could pass sound and try to adjust the brake balance. Just needed a few clicks to the front and I haven't touched it since. After the balance was in check we activated the ABS for back-up.

Second session we were able to mix it up a bit with the class leaders, build a bit of confidence. The car is quite a bit quicker than the BSR or any other car I've driven regularly so it took a couple sessions to really settle in.

Third session I went ahead on put on our first set of new tires on the car, Yokohama 250/650's in front and 280/680's in rear in the Medium(002) compound. What a difference, dropped a few seconds and started to run top times in the class as well as the following session when I got down to last years class pole qual times. I was absolutely thrilled that the car ran all day, and getting some great times out of it without any adjustment other than brake bias set-up.

Next morning the weather had cooled down and we started dropping more time. Down to an astonishing 1:33:9! My goal when the car was developed was to be 1:34's, and we got there in just a handful of sessions. I was able to back it up with another 1:33:9 in qualifying and was 4th overall behind a few 3.8L & 4.0L cup cars.

The race was pretty much the same story, finishing fourth overall and first in class. Feeling great after hundreds of hours in the car and nine months off track paid off with a win and two FREE Yoko slicks as a prize.

Third day on track I was able to drop to a best of 1:33:695 in qualifying. I lost a spot at the start, and another later on going too deep into T2, but got them back for a second win of the weekend. Four FREE yoko slicks, woohoo!

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corkscrew drive by in GT Boxster on Vimeo

my girly car does shoot flames now! That's about 3 feet through four mufflers...

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the qualifying flyer!! Much cleaner lap and driving than the race

LS Qual lap in GT Boxster - YouTube

...and here it is!! The Sunday GT3 class race video from inside the HRG GT3 Boxster.

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just a few more shots from the weekend. Yes, I'm thoroughly obsessed and pleased with the car...

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VERY nice! Great write up. Nice pictures. Outstanding race car!!

Amazing work. Good for you :cheers:

I love your car Eric, and always look forward to updates (and some of those parts becoming available for sale ;) ).

The GT3 control arms that you removed, are they by any chance available for sale now?

Truly a great read. I can only imagine the perma grin you had running her around Laguna. That is a kick ass track on my bike, I can only imagine it in your car. Thank you for the write up and most of all...the pictures!

Very nice. Can you post up where you purchased your front bumper and lip from? Cost? Thank you

I'm constantly amazed at the talents, skills, and ingenuity of the members on this board!


Thank you for posting.

Have a GREAT long weekend everyone.

Thanks! but the control arms made their way on to the girlfriends car already ;)

Ohh yeah! I was seen screaming and hugging people many times when I get out of the car haha. Such a blast to drive the car, and Laguna Seca just has that special feel to it. Getting home this week and comparing the lap times to all the pro series was fun too!