eric523

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.

The class choices I have in local GT racing is a power to weight ratio of 11.51 lbs per horsepower for GT4, or 9.01 lbs per horsepower for GT3. The dyno tuning will ultimately decide the final class with adjustment of weight, but I'm thinking GT3 is the leading option. Faster car all around, why not go as fast as we can and chase down some cup cars. The front runners in the GT3 class regularly qualify and finish ahead of 996 and even a few 997 cups.

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



Ready to come apart



Some of the goods

failed ims shaft 3.6L M96 motor






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.









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.

eric523

I purchased the gearbox from a RL member a few months back. I had already gotten an estimate to build the exact box from California Motorsports and definitely saved myself a few pennies.

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...th%20gears.pdf







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

eric523

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 be completed with Eibach main and tender springs. Spring rates are going to be an interested trial period.





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.



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.

eric523

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.











off to the body shop...









now ready for some flairs





Project has taken more time and money than expected(when don't they?) I'll keep updated as it progresses a little more over the next month. Might be an interesting path for other Boxster track cars to follow in the future!

jdistefa

Eric, going to run the new Rennline rear subframe strut bar?

What are you doing with your Gt3 control arms?

Helluva project, subscribed

eric523

I hadn't seen the Rennline bar before you mentioned it. We may consider using something to stiffen up the rear as needed, but we would most likely make up something ourselves.

GT3 control arms went onto my girlfriends car already...

Thanks, this was supposed to be simple motor/trans swap...ohh well, should be fun when completed.

J richard

Doh! I was thinking simple engine swap too! Looks killer have any target on lap times?

eric523

Yeah, project creep has set in...

On the short list of things to do still is:
Install Pectel ECU, new harness, and tune
Install new Motec CDL dash and harness
Install wireless network and harness
Install electric power steering system
Install carbon doors
Fabricate and install flat floor and splitter
Fabricate and install new roof
Fabricate and install rear wing
Fabricate and install new airbox
Flair rear fenders and repaint
Install dual brake masters and upgrade ABS system
Install polycarbonate windshield and side windows(along with new roof)
Fabricate and install new headers and exhaust system, and a 103db system, and a 90db system...

Target lap times will be 1:24 at WSIR, 1:34 at Laguna, 1:44 at AAA speedway. They'll get there, we'll just have to see how long it takes.

Ohh, and I already acquired a broken 997 3.8L motor for the next class upgrade a year or two down the road.

Brinkley

Eric,
I can't wait for more pictures and info. You are doing a lot of the things I have done with my Boxster S since 2005.

3.6L unfortunately It hasn't been cracked open for the high-end rods etc.
Motec M800, Custom wiring loom, Motec Dash with data.
Moton 15 way double adjustable remote reservoirs shocks.
Eibach springs of various rates.
Guards Transmission LSD.
LWFL.
Same wheel widths front and rear with Hoosier slicks.
Weight reduced to the lower end of what you are describing (2450 w/o driver full wet).
Rear fenders flared but not to your degree.
Double side air scoops re-routed to custom airbox.
Lexan windscreen.

Can't wait to see how you approach the air intake and airbox on your creation. You showed some half-shafts, what have you done here? Something doesn't look stock there. Am I wrong?

More pics when you can.

Brinkley

kcpaz

What are you doing for rear flares? Custom? Front fender flares turned around?

eric523

Thanks, I'll keep the thread updated up to and after the car gets to stretch its legs on track. I actually came across your car and a video at the end of last year when considering the 3.6L with a stand alone ECU. I originally had an M800 unit but sold it off for a Pectel to stay more consistent with some customer cars that are running the Pectel.

We're still considering a couple options on the airbox. The dual side intakes have been discussed but we were a bit worried about the resulting engine compartment temps. Any advise or data you would care to share? I've also seen them in the rear trunk, a large box on one side... I'll let you know how it goes.

The half shafts are stock Boxster S. We put them together with some GKN motorsports "aero" cv boots, and the CV's have been machined a bit just to get a bit of extra cooling.

eric523

We're working on some modified 996GT3R flares from Getty right now. I'm trying to keep the car looking like an early 996 cup or GT3R era car. The cup bumper looks a little dated but hopefully it keeps me from chasing the latest aero, front fenders, headlights combo etc. Trying to stay "baby cupish"

I believe you used the AIR flares on yours? I considered them, but already had these others laying around the shop. Figured I'd give them a try.

kcpaz

Yeah, I used the AIR flares... and then put a BUNCH of work into them to make them work and look nice and make the rear bumper removable. Still contemplating having molds made off of the quarter panels and rear bumper but I'll probably wait until I'm done with all of the aero mods. Still have side skirts to do.

eric523

Nice. I don't think I'm going to continue the flare to the rear bumper or change the GT3 style side skirts I have. Hopefully it saves a bit of work and I still get the bulge I'm looking for. I can easily fit the 280 Yokohama's right now but we're trying to make room for the possibility of a 320 slick if I decide to go bigger with the next motor. I'll post up a few pictures soon, we're working on them today.

If you had the molds done and were producing some, I would have certainly been interested.

kcpaz

I'll keep that in mind. The plan is to have the ability to remake all of the custom parts in carbon fiber. I've got roughly 80-100lbs I need to lose from the car