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'99 RS coupe for track use, Cusco diff, Carbon body panels, Custom Machining, Pic heavy...

8166 Views 61 Replies 13 Participants Last post by  TopElement
updated 9/27/21 -Cusco rear LSD install

Story:

A little backstory on what got me interested in Subaru's before I even started looking for a 2.5RS coupe.
About 10 years ago, met the guys from Renner Motorsport and started seeing all of the high quality builds they were working on. Most of them were for customers, but Peter and Ivo's (RIP) own cars were the best examples by far.
Widebody coupes, 500hp+ turbo motors, and flawless execution inside and out really got me thinking about adding a Subaru to the garage.
Since I already had a track car and fun daily drivers, I didn't want an old slow 2.5RS yet. Went to the Subaru dealer in early 2012 and ordered a STI hatchback in World Rally Blue. The STI finally arrived from Japan in April of 2012, and it was fun to drive with AWD and almost endless traction. After a few years, I started considering taking on a project of a 2.5RS coupe with a full STI drivetrain.
Why a coupe? It had to be a coupe because #1. 4 doors are stupid looking #2. Ivo had shared his opinion years ago and I agreed that only the 2 door cars are worth building.

So fast forward to 2015 and I've been looking everywhere for a 1999-2001 2.5RS coupe. Literally searching all across the country, on every car site, and even saw a clean example parked in Indianapolis and left a note on the windshield with an offer to buy it (no response from the jerk!). Plenty of ugly 4 doors for sale, some rusty 2 doors for sale, and almost zero stock coupes in good condition.

My fiance (now wife) and I were going up to San Francisco for the weekend to check out Fleet Week in October, so I searched on Craigslist SF and happened to come across a clean white '99 coupe for sale posted earlier that day! Contacted the owner so I could check out the car while I was in the area, and damned luck he was out of town that weekend. I got on the phone with the seller to arrange the sale, and as expected he had already received numerous inquires. I offered to Paypal a significant amount as a deposit, but he gave me his word he would hold it.

At this point it's mid-October 2015, and just a few weeks from getting married. My fiance (now wife) was not thrilled at me buying another car and going to get it. As us car guys do, I explained how great of an idea it was and immediately booked a one-way flight. Flew into SF and within an hour met the seller in a downtown parking lot. Gave the car a quick look inside and out, test drove around the block (and noticed a strange engine knock), and handed over $7k cash to the seller in exchange for a pink slip. That night drove back home to SoCal.

Goal for the car? Turn it into a rally beast and occasional track day fun.


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Some new equipment to help set up the car properly.

Set of Intercomp digital scales for corner balancing! Might go a little crazy weighing all my cars just to know how much they really weigh and understand F/R% weight distribution. Will weigh the trailer too, to get a baseline before modding it.
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Nice to see another track GC. 240 WHP with no lag and natural throttle response sounds nice!
You gonna share any specs on the motor? 2.5 destroked to 2.3? Do you have to stay N/A for your class?
You gonna share any specs on the motor? 2.5 destroked to 2.3? Do you have to stay N/A for your class?
Not building the car to any class, it's just a track day fun car.

I really enjoy naturally aspirated motor performance, so just seeing what can be done with a fully built flat four. Keeps weight down too, with no turbo, intercooler, wastegate, BOV, etc. off the front end.
Tom at TWE will give me final specs on the motor, but I asked for the most displacement possible with a goal of 9k rpm or higher. If the airflow is there, then 125hp/L should not be too difficult.
Nice to see another track GC. 240 WHP with no lag and natural throttle response sounds nice!
For now it's not too bad with the 2.0L motor, except the straight at Laguna Seca seems awfully long. Streets of Willow is ideal and more about handling.
Until the race motor arrives the focus is on making everything as light as possible and dialing in suspension and drivetrain. Then add 100+ hp and really have fun!

See you at the track. Taking the GT3 to Thermal Club in November, otherwise just using the Suby around SoCal tracks because of the terrible run-off areas that will destroy cars!
Well Subiefest autocross got cancelled because the event got moved last minute. Sucks but at least not missing out on 90 seconds of driving!

Pushing ahead anyway to put the car together and back on the track with cooler weather. Ordering Hoosier R7's and a new set of RPF1's for road course use. The Advans will be used to transport and store the car, and I'll try the Hoosier A7's at Laguna Seca to see how they last.

Cusco LSD with ring gear installed. A little tricky to hold the diff case without damaging it while torquing the bolts. Used rubber faced soft jaws on the bench vise.


Heated up the side bearing carriers to ~250 F, while the outer races were frozen for a couple of hours. With a little oil on the parts the races went in smoothly with some light taps and didn't have to use the press.


Then worked on grinding down the "nubs" inside the diff carrier. Never understood why this was necessary and now I know! Since the body of the Cusco LSD is larger than the puny open diff it can't move to the right so much when being installed, so clearance is needed on the left to put the diff in and rotate into position.



Cusco LSD for the R160 in its new home replacing the open diff on a 1999 2.5RS.
Checked tooth contact pattern again, this time with white paint. Spot on with no changes in shims.
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Nicely done! Going from open to torsen rear LSD was like magic on mine.
Subie is almost back in one piece to drive on track. Hoping to get on track over the winter.

For now, enjoying the GT3 on track. Off the production line it's ready for track days!

Love seeing you motivated to keep the cars going. Even as you have more modern faster cars to play with. I am the same.
Just checking in here. Finally got the 2.5RS on the ground with new Cusco LSD and axles. Been nearly 2 years that it's been on stands.
Need to fab and install roll cage and get a new windshield installed to get it back on the track. Carbon doors and dash in process to shave ~120lbs.

For now been busy doing this on the weekends:
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Nearly a year without updates. Subiefest is coming up again in July, so crunch time to put the car together and go for a gold trophy in the track competition!

Busy lately building up my new Bronco, outfitting the race trailer, and getting the GT3 ready for track season starting at Laguna Seca.

2.5RS needs at least a windshield and Cusco LSD break-in to be ready for action.
you ever go to buttonwillow?
Yeah, but don't think it's worth the 150 mile drive for me. Waiting for their new track to open up.

Streets of Willow, Fontana before it closed, and Laguna Seca are mostly where I drive.
Buttoning up the car and getting some fresh fluids in. Prepping for an autox test session to dial in the setup before Subiefest.

Making sure everything is torqued and alignment is good with new rear suspension adjustability.


Swapping out 17mm road course RSB for 20mm autox RSB.



Custom machined adapters to fit 17mm RSB in 22mm bushings.
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Brand new body panels from Subaru to reproduce in lightweight full carbon versions...

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Brand new body panels from Subaru to reproduce in lightweight full carbon versions...
Interesting …..
are you gonna be doing the molds and carbon layup?
Interesting ….. are you gonna be doing the molds and carbon layup?
That is correct! Carbon hood, doors, and trunk.
Roof will probably come from Marsh Composites, since I haven't been able to source a brand new non-sunroof roof panel.
And the goodies keep rolling in!
Whiteline 22mm front anti-roll bar.

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Coming in at 2,241 lbs with carbon doors, but OEM hood, roof, and trunk! Little over 1/4 tank here.
For sure under 2,200 lbs with a little more work. Lighter than a Miata but with AWD. :)

Even 50% cross weights (still 50% with me in the race seat.) Definitely need to work on that 58% front weight distribution though.

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That is correct! Carbon hood, doors, and trunk.
Roof will probably come from Marsh Composites, since I haven't been able to source a brand new non-sunroof roof panel.
Have you looked into Seibon Carbon doors? They sell carbon fiber doors for the coupe. I think they sell the trunk too. Question I have regarding the doors, I'm assuming you're not worrying about there not being a crash bar in the door bc your car is caged? Also are you using door cards or is it bare?

Would you consider selling carbon doors or other parts that you make?
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