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

8134 Views 61 Replies 13 Participants Last post by  TopElement
updated 9/27/21 -Cusco rear LSD install


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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Finally another update

Picking up the story towards the end of 2018.

After taking home a trophy at Subiefest for "Fastest NA-AWD", the car sat in the warehouse for several months.
Speedventures does a yearly summer event at Laguna Seca, so I quickly signed up for June 2019. In order to really get ready for track action, a few parts were ordered.

-Wilwood 6 piston front brake kit with 2-piece rotors
-Wilwood 4 piston rear brake kit with 2-piece rotors
-Whiteline front and rear end link set
-Whiteline roll center adjusting tie rods and ball joints
-Whiteline rear sway bar mounts for 22mm bar
-WRX 17mm rear sway bar
-Whiteline front strut tower bar
-Cusco rear strut tower bar
-Injen cold air intake
-PST carbon fiber driveshaft
-Inferno Fab headers and J pipe
-Delicious Tuning "Spork" ECU programmer
-(2) Griffin radiators
-(3) Setrab coolers for oil, power steering, misc

Also dusted off the TIG welder and fabricated chromoly rear suspension links with heavy duty rod ends, and spindle-mounted aluminum front brake ducts.

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Some pics from the track event at Laguna Seca.

As these things go, ran out of time before the event to install all of the parts. Installing a custom radiator, and plumbing/installing an oil cooler properly were going to require quite a few hours of fab work so they didn’t get done. The Injen intake didn’t fit easily, so it went to the end of the line. The headers were low priority along with the straight-piped mid section, so didn’t get installed. Lastly the “Spork” tuner requires a Bluetooth laptop and downloading ECU data, sending to Delicious Tuning, then uploading a tune. No time for that, and didn’t want to risk a bricked ECU just days before an event.

Loaded the car into the enclosed trailer on Saturday morning, along with several bins of supplies, tool chest, generator, air compressor, and pit setup. Hit the road from LA and headed to Laguna Seca.

Six hours later arrived at the track in time to drop off the trailer and head to the Hyatt Regency just a few miles from the track. The hotel was glad to offer oversize parking for truck and trailer after the event, so that’s a definite plus.

Overall the car did great on track. Didn’t even get to bed the brake pads until just before my first session, by driving around the perimeter road. The Wilwood PolyMatrix compound H race-only pads had zero fade all day. The caliper temp strips didn’t even register on the low scale, so I may need to use a lower temp range. Was able to brake later than anybody in my run groups, so while most (if not all) the cars had a horsepower advantage, passes on the inside of turns weren't too difficult.
Oil temps were getting to 250º after about 4 laps, and stayed there for the rest of the ~10 laps per session. Definitely need to get a cooler on there.
The Advan A052’s worked great in the 75º weather, and never got greasy pushing hard every 20 minute session. Outside edges looked fine with 2.5 degrees of front camber, although the inside grooves did get a bit feathered. No chunking due to the track focused design.

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Just getting back to these forums. Man do they look different, and not at all for the better!

Haven't posted since a very disappointing Subiefest AutoX event in 2019. Showed up early and prepared with my pit equipment and autocross Hoosiers, only to encounter a very cramped pit area where I couldn't even put up the canopy and the track surface was extremely dirty with loose asphalt/gravel that had the tires spinning and sliding around the entire course. Way too short of a lap too, under 30 seconds for most. Had to be in by 8am, but our group didn't run until the afternoon so we just baked in the SoCal sun all day.
Even with the tires sliding on gravel going into each braking zone, and understeering due to me using a poor choice of tire for the conditions, managed to barely pull out a win for the NA category. Not too far off from overall fastest time either. Lesson learned on tire choice, although the organizer could also plan ahead and clean up the course.

Leading up to the event I found a small coolant leak, which turned out to be from the water pump. So took care of new water pump and timing belt. Also had time after the Laguna Seca event to install the intake and headers, and get the Hoosiers mounted on an extra set of RPF1's. Almost forgot to switch out the race pads for autocross pads, so got that done the day before but got too lazy to bleed the lines.

New headers have much better clearance around the oil filter. Very high quality work by Inferno Fab, and better sound than the Borla.

Intake wrapped with DEI gold foil, and still more engine bay clean-up to do.

Not the right choice for loose surfaces!

Rolling up to the event early, to get the car out of the trailer and hopefully be towards the front of the staging line for a good pit spot.

A lot of effort for this little thing!

Need to find the rest of the pictures and video from the event.
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Picked up a new toy, and will probably use this one to tow the track car to local events.

2020 Raptor. Already have Cobb stage 1 and transmission control reflash. So much quicker than my STi, and don't have to worry about dips or driveways!

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Small update.

One of the upgrades for this year to improve traction and make sure all 4 tires are pulling through turns.

And a shot I found online from Subiefest last year, on the way to a fastest lap for the N/A class. This year the car has more power, more traction, less weight. :)
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So little time these days for the 2.5RS. With Subiefest on again for this year, the car needs to be put back together with numerous lightweight parts.

Instead of working on the track car, been having fun driving the new toy in the canyons and revving to 9k!

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Slow going on this! Between enjoying my other cars, raising two little kids, and getting the RSTI to the paint shop for new bodywork and a full color change, so little time for the track car.

Current state, which needs to change ASAP by the time Subiefest comes around. Original dash and doors not going back on, along with some other goodies if time allows...
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Too many parts laying around that are no longer needed and going to post them up for sale.

If anyone needs a '99 2.5RS dash, sunroof assembly, or other interior parts in the LA area let me know. Stock hood available soon too.

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Do you happen to have the drivers side window switch cover plate?
Do you happen to have the drivers side window switch cover plate?
I think so. Might have a spare in beige.
Subiefest is fast approaching for this year! Going through some old pics that had not been posted.

Preparing in 2019, with the RSTI in the background getting ready to go to the paint shop:

New set of tires just for this event. They've now been used a total of less than 2 miles!

Back on the trailer ready to go home.
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Still very little progress on the track car and running out of time!

Some of the attention has been on the RSTI, and maybe it needs its own build thread.

Nardo Grey complete repaint coming along by the body shop:

Base coat, still needs clear. Will be a lot of work to put it back together flawlessly!
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Might have to update the title after this! Engine build plans are being finalized with Tom at TWE for a naturally aspirated motor build with a goal of 240awhp+. :) 12:1 compression, 9,000 rpms, and more.
Still a few months before engine can be shipped and installed, but aiming to try it out at Laguna Seca in '22.

For now, added an enclosed trailer to the mix. Will build it out with tool storage and pit equipment. So much better than using an open trailer!

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Bringing the RSTI home after a complete paint job, in the new trailer.

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Went to install Cusco rear camber plates this morning, only to discover they don't match the bolt pattern of the rear shock towers! Not sure why I bought these a couple of years ago thinking they would fit. ISC camber plates have now been ordered.

Really need to correct the camber curve on the rear, as the camber goes positive with a little body roll and it's not ideal for outside tire grip.

Was ready to machine new spring top mounts to fit under the camber plates because the Teins have squishy bushings attaching the damper to the top mount and a thick rubber washer between the spring and upper perch. Terrible for precision damping control with the rubber doing most of the work on initial bump and rebound.

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Also finally replaced OEM heavy bumper beams with brand new JDM lightweight versions I've had in boxes for years. Installed aluminum threaded inserts in place of all plastic clip mounts. I do this on as many locations as possible to avoid having to deal with plastic fasteners again.

USDM front beam- 36lbs
JDM front beam- 7.6 lbs
USDM rear beam- 30.6 lbs
JDM rear beam- 4.7 lbs

53 easy pounds removed! And from the ends of the car where they most affect steering response.

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Realized a week ago that the Cusco camber plates don't fit, so ISC rear camber plates were ordered and have now arrived.

They match up to the shock towers, but now the upper spring mounts don't work with the Tein suspension! ISC mounts are for 2.5" ID springs, and the Teins are 2.75". So I'll be machining stainless steel upper spring mounts.

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A little bit of machining over the weekend. Made stainless steel upper spring mounts and spacers to fit under the rear ISC camber plates and into the spherical bearing.

Starting with this:

Some lathe work to produce the bumpstop surface and seat for the spring top:

Taper on top to make it look nicer and shave some weight:

Finished parts. A little heavier than I would like, but much stronger than aluminum and will not corrode

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Now the ISC rear camber plates work with the Tein coilovers!

Assembled and ready to add some rear camber for better contact patch. There is now zero rubber in the rear coilover to improve precision versus the original rubber spring seat and rubber bushings holding the damper shaft to the original upper mount.

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Was able to get some more work in yesterday to prepare for several upcoming events.

Have had this Cusco diff sitting in a box for quite some time, and finally opened it up to adjust it before installation.

Really don't feel like pulling the diff out again to make any changes, so hoping the initial setup works well enough for anything from Subiefest autocross wins to Laguna Seca track weekends.
Went with 8 of 12 springs for lower initial torque, and arranged the plates for 60% lockup. Left it at 1.5 way settings, though it can be set to 2 way action. For the N/A power levels it should be fine, and a turbo car with double the torque might need more lockup.

Carefully reassembled and applied a light coating of Cusco LSD oil to everything so nothing is dry on the first drive.

Opened up the diff housing, which may be the first time in its 140k mile life on the car. No visible metal particles, and gears show very little wear. Checked the ring gear tooth wear pattern before removal, and the contact is nice at about 2/3 of the height of the tooth but a little more towards the toe of the teeth than I would like. Will leave it as is though, because pinion shimming is a pain and it has been fine this long from the factory.
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