Rods Similar to the piston section, forged units will give you the best performance and insurance. But if you're looking for a cheap upgrade, Integra LS B18B rods are much thicker and stronger than the factory D engine counterparts. Used LS rods can be had for cheap but do require a bit of machining to work. Bang: N/A Bucks: $400+
Turbo Just like the B series section complete turbo kits can be had from Drag, Full Race, GReddy, PeakBoost and Rev Hard to name a few. Custom manifolds suppliers include AFI, Full Race, LoveFab and PeakBoost. One very popular cheap solution for a turbo manifold is to run the factory '88-91 CRX HF exhaust manifold with an adapter to bolt on small turbos. BMC Race is one of the companies that offers the adapters if you cannot fab one up yourself. Bang: estimated +80hp Bucks: $2500+
Supercharger All supercharger kits for the D series have been discontinued (Endyn, Jackson Racing and HKS). You will have to look for these kits used or build a custom setup. Bang: estimated +80hp Bucks: N/A
F Series (F20C/F22C) Mild Intake Intakes for this engine generally range from aluminum piping, to very expensive carbon chambers. The favorite for most S2000 owners would most likely be the J's Racing intake. There are several other brands that also offer an intake ranging from all different prices (AEM, ASM, K&N, Mugen and Password JDM). Bang: estimated +7hp Bucks: $250+
Exhaust Depending on what you're looking for in an exhaust (power, look, weight, noise level) the optimum piece can differ. Amuse and J's Racing both make an exhaust with absolute performance in mind, but the noise level and price is not for everyone. Companies like ASM and Mugen offer units that are quieter but also weigh more. Bang: estimated +7hp Bucks: $700+
Header Not everyone can be Elliott Moran and afford to cover his S2000 in J's Racing parts. Although the J's Racing header is one of the best out there, you can't rule out the ASM, Amuse, Hytech, Toda or so many other units. Bang: estimated +10hp Bucks: $800+
Medium Drivetrain Changing out the final gear of the drivetrain is probably more popular on the F20C/F22C than on any other engine in the Honda tuner world. Not having an incredible amount of torque from the engine, the factory 4.10 gear just doesn't cut it. Aftermarket kit options are 4.44, 4.57, 4.62 and 4.77. And yes it is true, Kia and Mazda units will fit and are much cheaper than aftermarket brands. Bang: n/a Bucks: $300+
ECU Tried and true is AEM's EMS unit that so many have used. And after a very long wait, Hondata has finally put together K-Pro to work with the F20C/F22C. Bang: estimated +15hp Bucks: $1400+
Wild Individual Throttle-Bodies For the utmost NA performance, ITB kits are available from Fuji Racing, Hayward Performance, Jenvey, Toda Racing, Tracy Sports and TWM. Bang: estimated +10hp Bucks: $2000+
Turbo Turbo kits are very popular with S2000 tuners, both complete kits and custom fabricated units. There are simply too many good brands to list them all here. Bang: estimated +100hp Bucks: $4000+
Supercharger Three names come to mind if you want to add a supercharger; CT Engineering (Comptech), KraftWerks and Vortech. All units are very impressive. Bang: estimated +100hp Bucks: $6000+
Mild Intake Results have shown that intakes with a 3" diameter pipe work best on a mild K20 engine. You can simply build your own intake using a large velocity stack from companies like Circuit Hero or Prototype Racing and mate them to a K&N cone filter. Bang: estimated +7hp Bucks: $50+
Header Some of the good yet less expensive K-series headers include DC Sports, HASport and K-Tuned. But if you want the absolute gain with no regard to price, than you should look into Hytech, R Crew Racing, Six Sigma Racing and SMSP. Bang: estimated +10hp Bucks: $400+