Cars Project Rex - a tuned GD-series Impreza for AC

[aphidgod]

Once upon a time in December 2014 I decided I wanted to bring my real-life project car into a driving sim to give it a good thrashing without risking financial ruin, death, or incarceration. I was also halfway through this rather extensive build and I wanted to use the simulator to help guide the rest of the process. That led me to check out the sim landscape on PC for the first time in a decade and that search led me to a readily-moddable Assetto Corsa, which was slated for public release the following week. (Score.) The rest is kinda history - those of you who've downloaded any of my other mods, know that they all owe their existence to this project. This is why (and how) I learned the physics engine in the first place. This is why I'm even here. It's time to see it through.

The idea behind this build was balance. It would have power - that's pretty easy to make in these cars - but it had to have everything else to support it in equal measure. I wanted the finished project to feel as solid and to be as docile and reliable as an OEM model, in addition to being super quick on the street and (on occasion) at the road course. The maximum power capacity of the gearbox established our ceiling at around 400whp, which we've achieved, so everything else is built around that number.

The physics for this car are based on numbers that have been meticulously measured, datalogged, calculated, or researched on IWSTI, NASIOC, or any of the other half-dozen Impreza owner/tuner forums on the internet. In addition to that, I built and tested the car so I know every part, every modification, every setting and every quirk and nuance of the setup. And I have had virtually unlimited time to drive the thing on real roads and bring those impressions into the game. (Not as easy as you might think, actually.) In total, though, you're not going to find a better-researched car anywhere, in any game, mod content or official.

The model is being worked on by @J-Lius , who is doing an excellent job so far. I'm providing measurements and reference photographs, he's working the magic. It's starting to come together, I think. (Maybe he will disagree. )

Sounds are not 100% confirmed, but I'm hoping to get permission from the RallyLegends guys to use the bank they have for the 22B, which is just about perfect for this car too.

As for the car itself, that'll make for a crazy long wall of text, so let's just leave the mod list for the next post.

 

[aphidgod]

Engine

• Cobb short ram air intake
• Silicone intake hoses, silicone Tomei turbo inlet
• Forced Performance 71HTA turbo (51lb/min flow) internal wastegate
• Grimmspeed top-mount intercooler
• Synchronic diverter valve (blowoff/bypass valve) set up as fully-recirculating, like stock
• Proflow Design ported OEM throttle body
• IAG billet aluminum TGV deletes
• Lightly ported/polished & gasket-matched cylinder heads, fresh build spring 2017
• Ported/polished + gasket-matched stock exhaust manifold
• Grimmspeed uppipe, crosspipe, divorced-wastegate downpipe with cat, all gaskets
• MadDad Whisper 3" catback exhaust - quietest 3" system on the market
• Okada Projects coilpacks + boots
• Denso Iridium spark plugs, 1 step colder
• Injector Dynamics 1000cc injectors, AEM 320lph fuel pump (for E85)
• Cobb fuel pressure monitor + flex-fuel sensor (yes, a flex-fuel capable GD)
• Grimmspeed lightweight crankshaft pulley, boost control solenoid, turbo heat shield
• Tomei billet timing belt guide, head gasket, ARP head studs/hardware
• Killer B strengthened oil pickup + improved windage tray
• Omni 4-bar MAP sensor

Driveline

• South Bend Clutch stage 3 organic-disc clutch w/ lightened flywheel
• JDM Spec C Type RA gear set (1-5) with stock 3.7 final drive and reverse
• Modena torque-biasing front differential
• Moore Performance transmission "blast plates" (gearset girdle)
• DSS one-piece carbon fiber driveshaft
• Subaru Group N motor/transmission/rear diff carrier mounts
• SuperPro billet pitch-stop mount
• Braided stainless steel clutch line

Suspension

• Racecomp Engineering "Regular Guy" Black springs (285F/265R lb/in)
• Fixed-perch 30-step adjustable dampers from Feal Suspension
• Subaru Group-N tophats at all 4 corners, poly bushes for all the links and arms F/R
• STI Spec C front lower control arms
• Whiteline Anti-Lift Kit (eliminates the OEM anti- geometry almost entirely)
• Whiteline Roll Center Kit (extended ball joints and tie rods to correct for ~1" drop)
• "Free Caster Mod" (A Subaru thing. Does what it says.)
• Whiteline 24mm adjustable ARBs at both ends (2-way front, 3-way rear) w/ poly bushes
• Kartboy billet aluminum ARB end links w/ poly bushes
• Camber bolts (front)
• MSI billet adjustable lateral links (rear)
• MSI tubular chromoly trailing arms (rear) - shorter than stock to adjust for ~1" drop

Brakes

• Stoptech slotted rotors
• Project Mu B-Force pads (street/track)
• Braided stainless lines
• High-temp racing fluid
• ^ It's ready for track days - the stock brakes are good - but this is still a street braking setup.
• APR front brake ducts - approximated in game, not installed (yet) IRL

Chassis/body/misc

• AutoMeter 52mm 30PSI boost gauge + digital wideband oxygen sensor/gauge
• SMY Clustermaker gauge pod for stealthy mounting of 2 gauges
• Turn-in Concepts fender cowl braces
• CarLabs Development rear X-brace
• Rear subframe lock bolts, poly outrigger bushings
• SuperPro poly steering rack bushings, Turn-in Concepts poly shift linkage bushings (assorted)
• EarthX lithium iron phosphate (LiFePO4) battery; 7.7lbs
• Secondary air pump system delete - not pictured
• Mishimoto all-aluminum radiator (~30% increased capacity vs. stock)
• Oswald Racing aluminum bumper beams (F/R) - done in game, not (yet) IRL
• JDM Red hazard button, S204 climate control knobs, Legacy (?) shift knob
• All interior plastic trim panels repainted in Crystal Grey Metallic (body color) by me
• Enkei PF01 wheels (17x8") - 17.4lb/ea (stock wheels = 23lbs) - not pictured
• Yokohama Advan AD08R (summer) or Michelin Pilot Sport A/S 3 (all-seasons in winter) - 235/45/17

Tuning

• All tuning (and datalogging) is done with a Cobb Accessport v3 and full flex-fuel retrofit
• All tuning is done by Eric Minehart of Torqued Performance, who is an actual wizard

 

[aphidgod]

This is a power graph generated from logged data on the road. The car currently runs a bit less power than this in AC, not because this is "goosed" (it's totally legit, collected on flat ground & corrected for temperature + exact weight of car/driver/fuel load) but it is a bit optimistic owing to the fact that I chose a crisp, dry, 28F night to do the pull. Happy turbo, happy car.

The data I used for the current power curve in AC came from a similar pull taken in the summer, on a ~75F evening at a more representative ~50% humidity. Unfortunately I can't seem to find that one anymore. I think it came out at around 383whp but without that extreme torque bump at 4200.

All of that will probably be moot when we finish tuning the current configuration. I've had some issues that have kept us from doing the last set of pulls, but the TGV deletes + head work we did this spring should really help out with that dead zone above 5500RPM - which the EJ255 heads are notorious for. We didn't go nuts recontouring the ports, but early logs do suggest it's a bit flatter at the top end.

 

[Phoenix77]

Very nice project
It's looking amazing... It goes without saying that with your attention to technical accuracy... it'll be just as amazing to drive.
Will be great getting hold of a Subaru in AC.
Good luck getting it finished mate

 

[aphidgod]

Thanks, John. I'm looking forward to getting it out. I think it's been long enough.

I suppose I should mention that I also have a set of physics for the 2004 STI in my library as well. There's quite a lot of '04 STI in my car, so once I'd measured everything up it was pretty easy to work backward to a stock setup. I know it won't quite fit this body style, but I can certainly release them as a pair.

 

[AccAkut]

Project REX ... didn't know AC had two wheel physics now

but cool to see a project car like that make its way into the sim... builds like that are practically impossible here, TÜV says no pretty fast

 

[Lowsound]

This.. looks.. amazing.

is the a plan to release this?



plz?

 

[aphidgod]

Absolutely. I'd release it tomorrow but Jouni would probably get mad at me.

We'll get there. Physics are all but finished, it's just getting a tweak here and there at this point as I drive the car on different tracks and reveal different behaviors. The only major aspect of the car for which I have no data is the dampers. I couldn't convince Feal to give me plots ( ) so for now that's done entirely by, ironically, feel. At this point the adjustments are pretty minute.

Some time in the next couple of years it'll probably be time to rebuild the struts. While they're off the car I plan to send a front and rear off to be professionally tested on a shock dyno. Would be so much easier if the builder would just give me the plots... oh well.

Wouldn't trade these struts for anything, though. They're perfect. Odi really knows his stuff. Short of something like an Ohlins setup, I think this is the best option available for a road-going GD.

 

[Lowsound]

Alright, fine. How much can I pay you to betray Jouni?
>

 

[aphidgod]

Not enough.

 

[fl4t.colin]

Any news? Really looking forward to this!

 

[Mascot]

Any news? Really looking forward to this!

I think @aphidgod quit the scene back in February so this is unlikely to see the light of day, unfortunately.

Edit: apparently not, he's back - my mistake!

 

[aphidgod]

I'd love to release this, guys, but the model isn't there yet and I don't know if it ever will be.

 

[Brownninja97]

I'd love to release this, guys, but the model isn't there yet and I don't know if it ever will be.

Oh crap you're back. its been quite a while.

 

[aphidgod]

"Back" is relative... don't expect me to post regularly going forward. But yeah, I'm still around. I quit RD, not AC.

 

[Leonardo Ratafiá]

 

[aphidgod]

All down to the model at this point. I'm pretty much done with the physics.

 

[Dave_6]

So happy to see you back on here @aphidgod !!!

 

[MoparMap]

So I realize this is probably a very lengthy answer and maybe not something you want to fully give away, but could you explain what all goes into creating the physics for a car (or at least your process)? What kind of information do you need and how does that translate to game files? I've looked through some of the unlocked cars to get an idea of how the data files work, but haven't dug into suspensions a lot, more powertrain stuff.

The short version being that I'd be happy to "drive" my own car in the game, even if the visual model isn't really there to back it up. I've got a 2004 Viper and have found some other Viper models out there, but most tend to gravitate toward either the ACR models, the originals, or the newest ones. As a "middle child" in the car's history, I often get left out. I've modified a different year Viper model that was unlocked to put in my powertrain info in and it feels reasonably good. I know the suspensions didn't really vary much in the later years (2004-2017) at least as far as hard points and geometry. Spring and shock rates changed I think, but I've got aftermarket ones anyway. That being said, I have no idea how good the suspension setup was in the model I downloaded.

I've got the car and engineering knowledge, but I'm not sure where I would begin. Was curious if you minded sharing how you went about things.

 

[aphidgod]

Well, you're correct in that it's a very long answer... there are quite a few files with many data points in each one, and the more of those you can measure or research, the better your car will be. (There will inevitably be some things you don't know, and in that case you have to set things up by feel, but the fewer, the better.)

As far as the Viper is concerned, if you'd like an unlocked set of files from our NFS Viper (an early 90s model) drop me a PM and I can share whatever's in there that might be useful. And I'm happy to help you modify them to better match your 04. It's a lot of fun driving your own car in AC.