Impreza 2.5rs (GC6/GM6) Owners - Can You Provide Feedback?

[FinanceGuy]

I'm considering buying a GC/M with an EJ25 (phase 2) power plant. It would be used for solo I and solo II. I just wanted to get some input from current owners to know what your experience has been with the car. Things like (but not limited to):

Stock vs modified?
NA vs boost?
Handling?
Things you must do to it before taking it to the track?
Optimal tire diameters?
Small mods that yield big results?
Common problems/concerns
Reliability (issues?)

Thanks for your input everyone!

[JoeT]

Mike Aversa is the king of GC

His record of setting FTD (Fastest Time of the Day) regardless of venue in Solo 2 (Autoslalom).

His setup: (setting FTD, before he added boost)
EJ25 NA
Headers
No Cat
Exhaust
Cams (Yoshio)

Suspension
Hot Bits (exactly like the ones for sale on this forum by KerryL)
Front spring rate: 9Kg
Rear Spring Rate: 9Kg
Camber: -3 degrees front
Camber: -2.5 degrees rear
0 Toe all around
1" lower than stock height

Car lightened as much as possible.

Tires:
You can use V710, Hoosier A6, or Toyo's, but for mike, it didn't matter what tires he used, he seemed to win.. LOL, note: Use the smallest wheel and tire combo with widest rim that will fit.

No real reliability issues for Solo 2

For Solo 1
Typical Subaru:

Add a catch can with recirculating oil pump
Spun bearing are the most common issue with the Flat 4


Special Note:
Regardless of what discipline you want to do, the biggest car mod with the maximum gain is suspension.

Go buy KerryL's hot bits and change the spring rates, and bolt them right onto your car and you'll be amazed.

[FinanceGuy]

Thanks Joe! Very informative.

Hopefully Mike shares his 2 cents as well.

[JoeT]

Mike is rarely on the board, but can be found at almost all racing events. We collectively all helped in sharing information to end up with that configuration.

Send him a PM, he's 101RS on this board.

[FinanceGuy]

Thanks Joe.

For the wheels, I was thinking something along the lines of Watanabe 15x8-8.5 and perhaps 15x10 rears (Google image search has good pics).

I'd keep the stock rotor diameter, but swap them for cross drilled.

Thoughts?

[STeveD]

Cross drilling is usually not the best way to reduce brake temperatures. GC brakes are already rather small, and you don't generally want to compromise on potential pad contact area. Depending on the pad compound you choose for Solo1, you may end up cracking the rotors rather easily.

Better to use ducting if you find your brakes are overheating in Solo 1. For SoloII, this won't be a problem.

[BryceD]

I didn't have any issues with brakes overheating this season. Blank front and rear OE rotors.

[Robin]

15x8? 15x9? 15x10? does those even exist for subaru?

i had a 1999 Impreza RS for 11.5 years.... Kerry's f/s ad is my old coilovers.... had those for 5 years.

My setup was total stock engine and had welded in 4pt rollbar. my main mods were 2002 wrx rear sway bar 20mm, master brake cylinder brace, front/rear strut bars , hp+ brake pads for street / autox (99-01RS have identical pads to 2002wrx) and Porterfield R4 race pads for track

For rotors, i always bought a new set every spring for the track.... the other set was simply for steet/winter use.

wheels
I had 15x7 45mm offset
- 1 set of team dynamic pro race 1 wheel
- 1 set of kosei k1 race wheel

both sets were 13lbs.

tire size was 225-50-15, The autox was great V710 race tires and track Toyo RA1.

Camber, with coilovers and extra set of camber bolts, i ran -3.3 front and -2.7 rear.

For brakes, if you do a lot of track, i'd suggest to get some brake ducts..... even with all the track/autox/tsd rallies, i changed the front wheel bearings twice over the years. pretty easy to do....

[Sir-knight]

if anything exists wider than 15x7 in subaru bolt patten, the problem then becomes how wide can you go before you start rubbing. Even 15x7s are hard to find, and wider than that you're looking at very expensive custom order volks or completely custom wheels.

I have a set of 15x7 that I can be persuaded to part with if you are looking, as my GD seems to like 16s better.

[alf]

www.realwheel.net, that's what I have in a 16x9. The 16" are about 10lbs. You can get them in a 15", from 15x8 to 15x18. when the car wheel don't fit anymore, get a truck wheel...

Get some real wheel;)

PS suspension modification not included...

[FinanceGuy]

15x10 would be pushing it, but it's been done!

http://www.rs25.com/forums/f5/133169-tiny-wheels-tires-n-advantage-3.html

Anyways, I just wanted to know what tire/rim combinations people have been running and having good results with.

Also, has anyone here boosted the stock engine or done a JDM swap?

[JoeT]

My legacy has a boosted EJ25 SOHC similar to the 2001 2.5RS. Custom cams, custom pistons, Autronic ECU custom injectors etc. etc. etc.

Not worth the effort, just get a swap, and put in forged pistons. There have been quite a few with JDM swaps, in particular the Version 7 or Version 8 with forged internals. They work very well.

[FinanceGuy]

Thanks Joe!

[FinanceGuy]

Here's a nice GC8 build:

http://blog.ameereehal.com/2011/08/1998-subaru-impreza-25rs-coupe/

[STeveD]

Okay, Solo1 track preparation and theory.... Off the top of my head:

#1: You have a Macpherson strut car that loses camber drastically with the G's that you generate. As you compress the suspension, toe changes drastically. Until you want to get into seriously stiff suspension, I recommend you plan your strategy around a very good street tire like a shaved Yokohama or Hankook RS3 that fits the street tire class.

#2: Oiling... The horizontal nature of the boxer motor means that long high-G corners like Turn 3 at Mosport Big Track start accumulating oil in the outside heads and it doesn't return to the pan very well. Keeping oil level high before every session is ESSENTIAL. Use a high zinc synthetic. Sticking with a street tire strategy will help to keep your G's down and your oil in the pan, but it wouldn't hurt more than your budget to consider an upsized oil pan with some good baffling and an oil cooler. If you're not going twinscroll anytime soon, the Moroso steel pan is a good deal and the Killer B is great quality. Most of us like the Cosworth pan baffle. Then, you're going to have to catch the oil vapours and make sure they don't go back into your intake because that will drop the octane value and give you detonation, so use an oil recovery system. Cheapest is Ixiz. Oiling priorities for track: High zinc oil, oil recovery system, larger pan, cooler. Consider the first two high priority and the last two unneccesary if you are staying with street tires, but nice to have. All of these mods are free in OTA (Solo 1.)

#3: Naturally aspirated or turbo... your cheapest way to do this is going to be STOCK motor. Ideally, naturally aspirated to keep fuel consumption down. Bad things happen to reliability when you deviate too far from stock components. Tunes from good tuners are safe, but probably not worth it on N/A without engine mods which are a spiral into hell. A tune on a turbo motor that doesn't adjust boost can make big gains. Get rid of the stock cats and use one high flow cat and it won't count for any PIP's in OTA. Full SPDA members get great deals on Vibrant cats at JRP.

#4: Heat dissipation.... your stock rad should be okay for N/A, but snag a turbo one (if you have the single row... check with Dan at Fourstar) if you can find one cheap. DON'T use aftermarket thermostats... terrible reliability and they fail CLOSED even though their marketing bullshit says they dont. You're better off drilling holes in a stock one if you need more cooling.

Your biggest concerns will be brake heat baking your wheel bearings and causing uneven pad transfer on your rotors. Fabbing some ducting from the front fog locations or from under the car to your front rotors will save you HUGE $$$. Subaru bearings don't scream when they're done... first thing that happens is pad knockback, which is a little scary going into turns 5 and 8 at Mosport. When they are so done they've scored your hubs ($$$) you get clicking. So the next step is that you might as well change your front bearings if they haven't been done in recent memory, but wash out and repack the Stock bearings with a good synthetic grease. Lucas Wheel Bearing grease and Amsoil synthetics have worked well for us. Just don't stay with stock grease... it's a waste of money. Scott at Can-Alignment (you'll go there anyway for setup) has a tool that lets him do it on the car, which will also help save you labour $$$ vs. trying to remove the hubs and putting it on a press if you can't do bearings yourself. Look at Powerflex bushings (Fourstar Motorsports) to replace your stock worn ones, or you can go heim joint for rear lateral links. Power steering cooler is not necessary. If you're not lowering the car drastically, a Whiteline ball joint/tie rod kit is decent quality for the price.

#5: Suspension... there's different levels of how serious you can get with this. Your essential PIP to take is alignment, and you should go to bushings as well. You have an old car, and you're going to have to change a lot of those, so an ALK with moderate to race bushing strength will be needed. You are going to want a LOT of front camber... think -3 degree ballpark, and increasing the caster wouldn't hurt. So consider a maximized camber plate setup for the front. You want the pillowball bearing PEGGED to the inner rearward strut tower housing (45 degree angle) for front camber / caster. Most off the shelf units don't do that, and are too thin / holey, so a custom top plate is really a good way to go. Change top rear strut bolts to camber bolts (Scott will help with that) for adjustability because there is none in the rear stock. If you're not lowering the car, you might be able to get more front camber with a second camber bolt... go with Scott's advice on this.

If you decide to go coilover, the used Hotbits DT1 coilovers are a fantastic buy in the other thread. They'll help you tune the car to eliminate the inherent tarmac understeer on this car. A slightly higher rear spring rate, and a higher rear ride height than front will help with rotation. DON'T over-lower the front of your Subaru... control sucks when you're using your bump stops under hard braking, especially on bumpy tracks like DDT and Shannonville. Peter Reilly at Hotbits.ca in Brampton can help you maximize these for travel and trim your bump stops to a safe level, and Scott @ Can-Alignment could do the same. If this car will be daily driven, don't go higher than 8KG front on the DT1's, so a 9 or 10kg rear will help it turn. Balance is the key here, and take a school if you aren't experienced with oversteer and understeer. If you decide to buy DT2's, you can maybe go to 9 in the front daily driven, depending on who makes the springs. Don't go to Hotbits RSI suspension for tarmac or daily driven... spring diameter is too wide (affecting tire choice) and they need to be removed and serviced regularly.

#6: Lightening... I haven't explored this to it's fullest, but if there was a model variant of your car that came without air conditioning that has the same handling index in Solo 1 you can consider removing the A/C. Stock seats are already pretty light, but keep yourself planted in the seat with a CG lock, or add 4 point belts over your stock 3 point. (Weird rule legality thing.) Pullies are free but most experienced shops recommend sticking with the stock unit for reliability.

#7: If you still have money falling out of your pockets, an upgraded CUSCO rear LSD will be free in OTA if your car already came with an LSD.

#8: Tranny... be gentle with your 5 speed. Time Attack isn't hard on it, but AWD autoslalom launches sure can be. Let your clutch be the loser in that battle. Stick with organic or cerametallic surface material if you will be launching (they recover better than kevlar.) Goiing to a stage four clutch on the 5 speed can hurt reliability because of the harshness of the engagement... an upgraded pressure plate is all you probably need at stock power levels. Use an oil mix that allows fast synchro engagement. The Redline MT90 (or Amsoil MTG) with Amsoil Severe Gear is a well proven mix. Short shifter is optional since unless you lighten your flywheel your revs won't match on fast shifting anyway. Lightened flywheel will speed your shifts, but sometimes is overpunished by the ruleset, so evaluate your PIP schedule first.

#9: Braking... Good fluid like Motul RBF600 or 660, a master cylinder brace (Cusco is better than Perrin, but ANYTHING helps here), coated stainless steel brakelines and good pads on stockish rotors work. I've become a fan of Performance Friction recently... think PFC-01's for the front (with separate rotors if you will have a different daily driving pad), and maybe PFC 97's in the rear, or just a Hawk HP+. the rears almost don't matter except for braking balance because they just don't get hot enough on a Subaru.

Those are my thoughts for now. Have to get ready for paintball.


Edit: I have a custom 7quart stock pan that needs cleaning, and GC stainless steel coated brakelines if you're interested.

[FinanceGuy]

Steve,

This is great. Thanks for taking the time to put this list together. Very insightful and helpful.

In response to some of your comments:

- I think N/A is where I'll start, unless I come across a JDM swapped setup for a good price. I've read that just by opening up the breathing on the EJ25 helps as well. Your tip on Oiling is well received. I was wondering about how the boxer would hold up under those conditions.

- I haven't decided if this will be a daily driver or not. If it is track only, then I'll likely gut it. But even if it is a daily, I'll want a bucket seat installed. I hate being thrown around and gripping the armrest and door handle just to stay planted in the seat.

- Suspension will be my starting point. I used to compete in CSCS Racing's drift events, so I do have some experience with understeer/oversteer. I prefer oversteer tendencies rather than under, so I'd like to tune the suspension to handle like a rear drive platform. I've run race spec coils (Megan Racing, not the best but good bang for your buck) on a daily driver and I totally regretted it due to the harsh ride. Bushings, strut braces, and sway bars will be installed with upgraded ones right away. Perhaps street spec coilovers will work for a daily driver?

- As for the diff, would you suggest I replace the front diff (assuming its Open) with a viscous or 1.5/2-way first before upgrading the rear?

- I can attest to the fact that brake ducting (DIY setup) makes a huge difference. I had no idea that the bearings were silent killers on the Subaru though!

- does anyone here fabricate custom top plates?

- Also, does it make sense to stick to a 15" rim diameter in order to maximize engine torque/acceleration? I've seen some GC6's with 15x7 and 15x8's (and one guy on 2.5rs.com with 15x10!!).

[STeveD]

I forgot about your drift experience, sorry.

If you're staying naturally aspirated, the 1.0 or 1.5 way front diff may not be worth the 1.5 PIP's and ~10 hours labour for changing the diff. 1.0 is easier to drive, and 2.0 is typically gravel only.

PeteM calls sway bars "the devil's tools" with good reason. For the front sway bar ... going stiffer in the front often hurts you in the understeer department. Consider leaving the front stock and make sure the rear is adjustable. Rate will depend on what spring rates you choose.

You can do street spring rates on the front coils, it's just the balance you need. 7kg front doesn't usually feel too bad, and 5.5kg is standard Hotbits. The front is most of the ride feel anyway. For the rear, when you stiffen it, consider a spring rate and length that will let you set the perch above the tire. I have extra 8kg KW race springs that might fit the bill for you.

There's a machinist in Mississauga that developed a custom CNC program to make plates for me. I'd tweak the design a little if I had the opportunity again. The adjustability I have in it... I never really use anyway; the plates are always maxed. Use 5/16" or 8mm thickness to help avoid doming if you're going to go agricultural or cut curbs. Mine below on the right, Sue's on the left, and below that the typical position installed and why I replaced that original plate.

http://spda-online.ca/modules/xoopsgallery/cache/albums/albuo22/Camber2.sized.jpg

http://spda-online.ca/uploads/forums/116_471ead9a87c08.jpg

And yes, I'm a big fan of keeping rim diameter as small as needed for lower weight, but mainly lower cost of rubber.

P.S.: If you're not doing a CASC_OR legal roll bar, maybe stick with a heavily bolstered lightweight reclining seat. Those are PIP free but still may allow you to slide out of the way in a roll. Race bucket and five points ONLY with a legal bar.

[Robin]

to run a really wide wheel, and wheel/tire sticks out, you'll need to run a really high spring rate.

ask alf.... that's what he does 16x9 on 265's for autox.

but for track? way too stiff for sure as he's over 10kg (can't remember his spring rates).

On OE power, I'd leave the front diff alone and front sway bar alone also. it's already a decent size front bar. 19-20mm but rear is tiny at 13mm....

if you're doing a lot of track, get ducts to help the bearings but overall on OE power it's not a car that's hard on brakes. espcially if you're going to reduce the overall weight. they're about 2820lbs from factory. so if you're going to gut it / bring it down, more weight, be great.

Luca 00rs race ready was pretty light. not sure if he posted a while back what he did.

[STeveD]

Robin wrote:

Luca 00rs race ready was pretty light. not sure if he posted a while back what he did.

Luca used to crack rotors running Hawk Blues at hard braking tracks like TMP. I think that Steve Pope and Paul M cracked more of them in their WRX's, but I do remember Luca cracking them as well. But the problem there was a lack of cooling and the abrasive and heavy heat nature of the Hawk Blues.

[FinanceGuy]

Man I love the depth of knowledge on this forum. I've been a member of other forums over the years and have never had consistent technical discussions (that are backed by someone's experience) like I've seen here. I've read the "High Performance Subaru Builder's Guide" back to back 3 times and yet I've gotten more out of the conversations here than in that book.

You guys are great!

[STeveD]

Ack! They're second nature now, so I forgot my two favourite non-STi brake mods:

- Kill the ABS before it kills you. ;-) (removing the fuse is enough)
- If you have as much trouble heel-toeing as I do with stock pedal heights (size 12EEEE shoes) go to Fourstar and have them weld you up an adjustable height brake pedal. 1 to 1.5 hours typically. You may want to adjust the gas pedal angle too depending on your size and heel-toe method. Best brake mod evar!

Legal disclaimer: you do this at your own risk, of your own volition, blah blah blah

[Robin]

hell no.... on track, loved the ABS in my RS. it only came one when really needed and not flat spot tires.

i hated it on gravel rallies... then i left foot braked too everywhere and then i disengaged the abs for drivex rallies.

[JoeT]

I love my ABS and with I had it on my Legacy, the ABF was awesome and let me dive in deep into corners.

[alf]

I miss the ABS on my car. If i can't sell my GC8, that's the first thing I'm fixing in the spring. No more flat spot and like Joe said, dive deeper...

[STeveD]

I like having ABS on the STi, but my 97 Legacy and the 2002 TS, it's just wrong for me. Comes on too soon and too severely. At the track where inputs are smoother, I just wouldn't use it on the older cars. Especially once it rains. Autoslalom with more rapid inputs, variable pavement, pebbles, oily surfaces, rain... sure.

To each his own. :-)

[JoeT]

Steve, agreed. For old farts where you take the same corner 30 times in on day, I agree. For the younger (at heart) with faster reflexes and take 30 corners 5 times in one day through varied grip levels, and requires instant adaption, we like our ABS specially with AFBD. LOL

[FinanceGuy]

I disabled ABS on my s13 and noticed tremendous increase in braking force. Back then I was also running larger diameter wheel/tire combinations and seemed to confuse the ABS system anyways.