How to build a competitive S2KC Street Class car...

This post is mainly for my friend who is in all likelihood going to buy an S2000 and join me, Fil, Nino and just about everyone else in the S2000 Challenge Series. The subject is: how to build a competitive S2000 Challenge Street Class car from a bone-stock non-CR S2000. I also hope to include a realistic cost analysis of the different modifications possible. So let's get started. First, the rules:

AERO
0.25 = air dam bumper, any add-on lip (including OEM), canards, wind deflector
0.50 = splitter
0.25 = diffuser
1.25 = level 1 wing (CR, APR200 low mount, Mugen)
2.25 = level 2 wing (Voltex, J's, APR300, APR200 high mount, C-West)

TIRE/WHEEL
0.75 = level 1 street tires (RT615, RS2, MX, CSC3, PS2)
1.50 = level 2 street tires (Z1, AD07, RE01R, R1R, 595RSR, NT05, RE070)
3.50 = R-comp (RA1, R888, NT01, A048, PSC)
1.00 = 235~265 front tires
0.5 = 9" wheel or wider and/or widening front/rear track with wheels or spacers lower than OEM offsets (front +55, rear +65, not counting camber effect)

POWER
0.25 = non-oem intake system or any mods to OEM intake (including filter, snorkel, or piping)
0.25 = non-oem header
0.25 = test pipe
0.25 = cat-back exhaust
0.75 = ECU
1.50 = engine internal mods
3.00 = FI

SUSPENSION
1.00 = non-coilover suspension including CR suspension
2.50 = coilover suspension

DRIVETRAIN
0.50 = clutch type LSD
0.75 = final drive

WEIGHT REDUCTION
0.25 = softtop removal (but you must run a hardtop). Note: Penalty for soft-top removal waived if you have a 4pt roll-bar, 5-6pt harness, and an approved race seat. Interior removal on installation of safety equipment are not penalized.
0.25 = passenger seat removal

Street Class is limited to 5 points.
Modified Class is limited to 11 points.
Anything above 11 points is Unlimited Class.

Let's begin...

Aerodynamics
I feel like the S2000 is decent, but not great in this category. It does generate a significant amount of high-speed lift, especially in the rear. That is, as speeds increase, lift increases and your cornering ability decreases. This could even be dangerous, especially at a track like Willow Springs International Raceway, where you should be apexing Turn 8 at over 110mph!

Therefore, a Level-1 wing is a must. I recommend the APR GTC-200 wing because it is light, adjustable and I think more efficient (i.e. more downforce, less drag). The CR wing will do as well, especially if you want that OEM look. Anything more would be a Level-2 wing, and would not be an efficient use of the 5 points allotted for Street Class. Front aerodynamics would also be quite nice, but not as necessary. In fact, I would recommend going with the rear wing first, then assessing the high-speed handling balance, then deciding whether or not to get front aero. On a staggered 225/255 tire setup, I found that rear wing induced too much understeer, and I hope to acquire front aero to help increase front grip. On a non-staggered 255/255 tire setup, front aero may induce too much oversteer.

1.25 = APR GTC-200 Wing - $530
0.25 = OEM CR Lip (optional) - $450

Tire/Wheel
The AP2 (MY2004+) S2000's come with 17" wheels, which are the perfect size for our needs. The wheel size is 17x7 +55 front, 17x8.5 +65 rear. The tire size is 215/45R17 front, 245/40R17 rear. There are two ways you can build a Street Class S2000 car, and it is based on which tire you choose: street tire or DOT-R tire.

The best street tire now is the Bridgestone Potenza RE-11, which is reported to be a full second quicker at a 1-minute 15-second course than its predecessor, the RE-01R (also another excellent tire). When DOT-R tires (Toyo R888) were tested, they were shown to be only 2 seconds quicker than same-sized RE-01R at a 2-minute 5-second course like Buttonwillow. So clearly, the RE-11 is closing the gap between street tire and R-compound tire. The R-compound may have the advantage over longer track sessions in the heat, but since S2000 challenge is Time-Trial based (you get two laps to make it count), R-comps may even have a hard time getting the tires up to temperature, while Street tires will be at their optimum operating range. Given this information, there are two options:

Street Tire: Since RE-11 is only 1.5 points, you can run a non-staggered setup with 255/40R17 tires all around for another point. On a budget, the Dunlop Z1 Star Specs can be used.

1.50 = Level 2 Street Tire (RE-11 or Z1 SS) - $945 (minus $100 rebate) or $713
1.00 = 255-width front tire
0.00 = AP2 Rear Wheels in Front - $400

DOT-R Tire: Since DOT-R tires are already 3.5 points, you don't have much room for anything else, especially if you're going with the rear wing. You are forced to use 225/45R17 front and 255/40R17 rear. If money is no object, the Toyo R888 would be a great choice (since the 225 front tire is much wider than any other 225-size tire), whereas if one is on a budget, the Nitto NT01 is the better alternative.

3.50 = DOT-R Tire (R888 or NT01) - $656 or $792

Suspension
This is completely dependent on what type of tire you choose, above. Again, if you're going with DOT-R, there is just no room for any non-OEM modifications. In fact, even CR suspension parts are excluded. So the best thing is to get the stiffest non-CR springs you can find. That would mean the front springs from MY2008-2009 (284lbs/in) and the rear springs from MY2002-2003 (306lbs/in). You could also go with the matching shock absorbers, but they're all valved so similarly and the spring rates are so close together, that it wouldn't make much difference, especially for the cost. Sway bars are a free modification--you can go with the thickest or thinnest OEM or aftermarket sway bars for no point penalty. Therefore, sway bars should be used to fine-tune the handling characteristics once everything else is set. You could even go with an adjustable sway bar to fine tune balance from one track to another.

If you decide to go with non-stagger street tires, then a very affordable solution is to go with CR suspension. CR has much stiffer spring rates (389lbs/in front, 349lbs/in rear) and increased damping force to match. The front-biased spring rates (i.e. the front springs are stiffer than the rear), would work perfectly with the non-stagger tire setup (since non-staggered tire setups on the S2000 chassis tends to induce a bit of oversteer). Or, you could use the CR shock absorbers and go with any aftermarket spring for even higher spring rates. If money is no object, then custom-valved Koni's with custom springs (for example 650lbs/in front and rear Hypercoil springs), would do very nicely! In fact, these may even be better than full coilover suspensions offered by the likes of KW or TEIN, without the 2.5-point penalty!

1.00 = non-coilover suspension

Prices:
CR-suspension used: $500-800 (recommended)
CR-suspension new: $1200
Custom Koni with Hypercoil: $3000+

Also, camber kits are free-mods. The S2000 has some camber adjustability, but its range is limited, especially in the front. For example, if you were to max out the camber front and rear, you would achieve something like -1.2 front camber and -2.4 rear camber. That is not nearly enough camber to make full use of the tires, and it will lead to rapid outer shoulder wear and even disintegration. There are two very good options:

SPC Performance Camber Kit - $170/pair
Pros: adjustable sliding bolt, increases dynamic camber
Cons: more moving parts

J's Racing Camber Kit - $400/pair
Pros: no moving parts, increases track, will correct suspension geometry if lowered
Cons: expensive

Engine / Power
This should be the last thing to modify, and should be approached only if there is free room for points. Two things definitely worth getting is a lightweight cat-back exhaust and the Berk Technology High-Flow Catalytic Converter. The OEM exhaust system weighs a staggering 65 pounds, and much of that weight is concentrated behind the rear axle (compared to 7 or 8lbs for titanium exhaust systems and 24lbs for stainless-steel ones). The exhaust is also very restrictive, and people have measured gains as large as 15 whp. So, if there is extra room for points, a cat-back exhaust with high-flow cat would be a very good option. I would recommend T1R 70R V3 ($850, stainless steel) or the T1R 70RT ($1400, titanium).

0.25 = Cat-Back Exhaust - $850 to $1400
0.00 = Berk High-Flow Cat - $250

Safety
Safety modifications are all considered free mods, but are definitely recommended. First, a bucket seat is probably the best investment you can make in terms of driver improvement. You are held in place snugly, allowing you to focus on driving rather than using your elbows and knees or even your hands to brace yourself against high lateral-Gs. A roll bar is also a worthwhile investment, and allows you the ability to use a 5-point harness for even more safety and comfort.

0.00 = Recaro SPG w/ Taitec Rail - $850
0.00 = Bethania Garage Roll Bar - $600
0.00 = Schroth 5-Point Harness - $275

Miscellaneous
Another excellent investment for driver improvement is a GPS Datalogger. GPS Datalogger systems such as RacePak G2X and Trackmate have GPS antennas that track your exact location on track 20 times a second and built-in accelerometers and computers to track your car inputs. You can see where you're not making the most out of your car, compare different driving lines and see which is faster, etc. The biggest advantage is being able to compare data with fellow drivers and seeing where they're faster than you and why. Therefore, the decision of which datalogger to buy should be based on which is more popular amongst your friends. Hint: I've got a G2X, and so will Fil very soon.

0.00 = G2X Datalogger - $850

Conclusion
So while the rules make it appear as though there are infinite ways to build an S2000 Challenge Street Class car, there are actually very few was to make one that is competitive. In reality, there are really only two ways.

Non-Stagger Street Tire
1.50 = Level-2 Street Tire (RE-11) - $845
1.00 = 255-Width Front Tire
1.00 = Non-Coilover Suspension - $800
1.25 = APR GTC-200 Wing - $530
0.25 = Option*
*Option: based on the combination above, if you need more front downforce, buy the CR front lip. If front downforce is not an issue and high-speed balance is good, buy the cat-back exhaust.

Free Mods
0.00 = AP2 Rear Wheel in Front - $400
0.00 = Camber Kit - $350-800
0.00 = Berk High-Flow Cat - $250
0.00 = Bucket Seat - $850
0.00 = Roll Bar - $600
0.00 = 5-Point Harness - $275
0.00 = GPS Datalogger - $800

Staggered DOT-R Tire
3.50 = DOT-R Tire (R888 or NT01) - $656
1.25 = APR GTC-200 Wing - $530
0.25 = OEM CR Lip - $450

Free Mods
0.00 = Optimize OEM non-CR spring - $120-240
0.00 = AP2 Rear Wheel in Front - $400
0.00 = 10mm Front Spacer - $120
0.00 = Camber Kit - $350-800
0.00 = Bucket Seat - $850
0.00 = Roll Bar - $600
0.00 = 5-Point Harness - $275
0.00 = GPS Datalogger - $800
0.00 = Berk HFC (probably small gains with OEM exhaust) - $250

Must Have Modifications
Regardless of whether or not you buy any of these above, there are some things you should do to keep the S2000 track worthy. This is mainly on brakes.

Carbotech XP10 Front, XP8 Rear Pads - $325
Centric Rotors - $190
Motul RBF600 - $17/bottle

Any questions, comments, opinions?