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

8029 Views 60 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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As mentioned in first post, the engine was knocking when first acquired. Of course this was the world famous rod knock of the EJ251 motor.
Car made the drive from San Francisco to LA just fine, although with knocking at revs over about 3k rpm. Maybe a little head gasket leak as well, since slight overheating happened at slow speeds in traffic.

Drove the car like this a few times around town, and knock got louder and rougher. Finally after about a one hour drive, it refused to start and engine seemed to have seized after cooling down.

Around Christmas of 2015, picked up a 2.0 n/a motor from Japan and replaced the original motor.

Machined a couple of aluminum plates to match the intake manifold bolt pattern, and used them to lift the engine and keep it balanced.

Some noise from the transmission in neutral, and would go away with clutch depressed. So since the transmission was out, replaced main shaft bearings, replaced absurdly heavy OEM flywheel with ACT Streetlite, and new Exedy organic disc with OEM style pressure plate.

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2.0 engine running well and transmission working smoothly, it was time to get the car out for some fun in the dirt. Signed up for a RallyX at Glen Helen, and got out there with everything stock.
Just like any OEM parts not intended for high performance, the all-season street tires were slow to respond to quick direction changes and did not grip very well in loose dirt. However the handling of the car was very neutral, and liftoff oversteer could be induced as well as a little oversteer under power with a zero toe rear alignment.

For better performance next time in the dirt, I ordered up a set of Team Dynamics rally wheels and DMack gravel rally tires. Massive difference in the dirt, and could now push hard with more grip and more puncture resistance.

Hitting the trails at Hungry Valley. At this point I recalled my buddy Ivo telling me years ago that he tried rally with the Subie and it beats up the car, so stick to road racing.

Some trail action in Gorman. Never seen another car, only some quads and dirtbikes.
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After driving the car stock at a few events, and old slow stock cars not really being fun street drivers, it was time to get rid of any parts that don't make it faster, more reliable, or better performing.

Ordered a pair of pro racing Sparco Ergo seats in different sizes for driver and co-driver, and a pair of OMP 3" 6-point harnesses.

To properly install the seats, I designed side-mount seat brackets and had them fabricated from 1/8" 4130 steel, waterjet cut, and powder coated. They are adjustable for front/back, up/down, and tilt. Lighter than Sparco steel mounts, and narrower to save space.

Since mounting seats to adapter brackets/sliders and bolting those to the stock seat rails on the chassis results in seats that are higher than they should be, and is also a half-ass way of doing things, the sheetmetal chassis rails were removed. Drilled out all of the spot welds, and ground the leftover nubs smooth.
Measured for seat location to determine where new mountings points would be. The drivers seat is placed for optimum driving position, which is determined by steering wheel and pedal position. It's a lot of work to move wheel and pedals back, for not much gain. The co-driver seat should go as far back and down as possible, so it was installed with the back almost touching the rear seat hump in the chassis.
I fabricated 1/8" steel plates to match the shape of the floor and side sills, and TIG welded them in. (Tip- tack weld in place, and grind away underbody coating to reduce smoke and fire!)

Once the mounting points were in place, square steel tubes were welded in. Quite tricky to grind the ends to match the mounting points, and get them level and parallel to properly install the seat.
I machined steel bushings for the harness mounting points, and welded them into the tubes.

Seats with harnesses finally installed. Takes a little driving to find the best seat position, especially tilt. Still missing shoulder harness bar.
Many people don't realize that the OEM setup actually has the driver seat offset from the steering wheel, it's stupid. The new setup has the driver seat centered with the steering wheel.

To round out the interior work, the dash was removed in order to take out all heating and cooling components, resulting in a pretty good weight saving. Sparco racing wheel was installed.

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With the cockpit better suited for high performance driving duties now, it was time to improve suspension and drivetrain for better handling and response.

First up was the easy stuff. Machined a couple of aluminum bushing inserts for the differential mount. This got rid of diff slop under power/decel.

Pic to follow

Then the T bar mounts. These are big squishy bushings that allow the T bar to move around, which allows the diff to move around. All of this causes drivetrain torque fluctuations, which doesn't help traction or make for a precise driving experience.
I designed lightweight solid mounts, and had them machined from 7075 aluminum and gold anodized. Pressed out the original squishy bushings, and put in the solid pieces. (Had about 20 of them made, so extras if you want them)

Next post will be pic heavy, showing stock squishy rubber bushings on the suspension replaced with spherical bearings.
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It's looking good. Btw I'd recommend using a different image hosting service like Imgur as Photobucket images have a huge water mark on them and are pixelated
yea whats with photobucket now? cant see anything in these pics
I designed lightweight solid mounts, and had them machined from 7075 aluminum and gold anodized. Pressed out the original squishy bushings, and put in the solid pieces. (Had about 20 of them made, so extras if you want them)

yea whats with photobucket now? cant see anything in these pics
Yeah, working on this. Photobucket really screwed everyone over. Should be fixed soon...
A few pictures for now of how the front control arm bushings are replaced with spherical bearings.
Remove squishy rubber bushings. Measure bushings and control arm. Find suitable spherical bearings and machine parts to make everything go together.
Started with a bar of 17-4 stainless steel for the control arm sleeve, and a slug of 7075 aluminum for the housing to hold the spherical bearing.

Squishy bushing that kills precise steering and smooth suspension articulation.

Remove nut and pull off bushing.

Always use high quality materials. "Aerospace grade" materials used for car parts is BS. Material is what it is, and you use it wherever.

Drilled for a tight slip fit onto the control arm, now machining the outside of the stainless steel sleeve.

Finishing the shoulder on the sleeve, which supports the inner portion of the bearing.

Test fitting a 1" ID spherical bearing. Precision machining, for a clearance of just .0005" aka slop free.

Sleeve counterbored to fit the expanded portion of control arm pin, and test fit.

Sleeve with bearing, installed on control arm. Next is making all of this fit the OEM aluminum mount that bolts to the chassis.
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Now making the housing to hold the spherical bushing in the OEM mount.

Make tools to remove stock old bushings.

Machine the mount so it's actually round. It was not round to start with, and the manufacturer probably just presses the original bushing in and allows it to distort to fit.
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Pictures should be fixed.
Machining the bearing housing. Goal is to make it a snug slip fit into the OEM mount, and for the bearing to be a snug slip fit as well. Holding tolerances of +/-.001"

Finished housings, ready to have bearings pressed in.

Heating up the housing so it expands enough to accept the bearing housing. You get one chance on the press to get in straight, otherwise it cools quickly and parts get stuck.

Mount with spherical bearing vs. OEM squishy bushing.
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With spherical bearings taken care of on the front control arms, steering became much more precise. Still slow with the OEM rack, but quicker response to inputs and more feedback. A little more noise into the cabin, but probably due mostly to lack of carpet and insulation.

Next thing thing tackled somewhere in 2017 was to get rid of the awful bushings in the rear trailing arms. The large rubber bushings allow slight changes to wheelbase under power and braking, and don't allow smooth articulation because they have to twist.

Old bushing

Bushing pressed out and bore given a little cleaning

Machined housing for spherical bearings from 7075 aluminum

Machined bearing inserts from 17-4 stainless steel

All the parts ready to go together

Ready to install the arm back in the car
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By the end of 2017, the car was just a toy that only comes out of storage 2-4 times a year and gets trailered to events.

Pictures from a RallyX event at Glen Helen. Unfortunately no action shots, but I'll try to find some video footage.

At Gorman, where the yearly rally is held on powerline access roads. This video is actually from 2016 before race seats were installed.
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With my daughter being born towards the end of 2017, the car sat in the warehouse until mid 2018 when I could get back to working on it.

Subiefest 2018 was announced, and there was going to be an autocross. So why not switch to a tarmac setup?

Since quality coilover options are now limited for this older platform, I settled for Tein Flex Z. Also ordered a couple sets of RPF1's in 17x7.5, and Advan's newest AO52 tires in a small 215/45/17 to keep rotating mass to a minimum. (I think RPF1's are quite ugly, especially in high offsets, but it's a strong and light quality wheel)

Expecting to trailer this car around for a few years to different events, I ordered a factory build of a 2018 Ford F350 and it arrived after about 3 months. Crew cab and long bed with 4wd off road package. 450hp and 935 ft-lb of torque is more than enough to take the little Suby anywhere. :)

Always need to test! So got out to California Speedway for a few autocross runs to scrub in the tires, and figure out alignment settings a couple weeks before Subiefest.

Loaded up for Subiefest 2018. Only a few miles from my house, but an old Subaru with track mods gets a little attention from cops, and don't need to risk any punctures.

Finally got out on the course in the afternoon, after being required to roll in at 7am and wait in the sun all day without a good schedule. Handling was decent, considering the only change from dirt to tarmac was coilovers and tires.
A lot of roll in the turns, so the inside tires weren't doing much for lap times.

Mission accomplished! 1st place in class, 3rd overall in a group of about 76 cars. Was within tenths of a second of the RSTI ahead and the winning BRZ. A field full of STI's with double or triple the power, and really wide tires, but that wasn't much benefit on the smallish autocross layout with dirty asphalt.
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Hello everyone,,
It's looking good. Btw I'd recommend using a different image hosting service like Imgur as Photobucket images have a huge water mark on them and are pixelated
Hello everyone,,
It's looking good. Btw I'd recommend using a different image hosting service like Imgur as Photobucket images have a huge water mark on them and are pixelated

All the pics should be fixed, and look ok to me.
I can see the pictures just fine
I can see the pictures just fine
Photobucket has limits on how much data you can use over a period of time. Once past that you get nasty looking pictures with huge watermarks. Might be a daily thing.
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