Model Year 2004
(Second generation S2000).
ENGINE
To improve torque output, Honda engineers stroked the all-aluminum four-cylinder 6.7mm to deliver another 160cc of displacement and a slightly undersquare configuration. By Honda's measurement, there's still 240 hp at your command, only it arrives at 7800 rpm, some 500 rpm lower than previously delivered. This is because the increase in piston speed from the long-stroke layout would stress the internals to the breaking point at a higher rpm. It's one of those physics things.
• Redline dropped from 9000 RPMs to 8000 RPMs.
• F20C engine code changed to F22C ( 2.2 liter) in North America market; the F20C (2.0 liter) remains in production elsewhere. Reportedly Greece gets the F22C too with engine code designation F22C1.
• Through the use of a longer stroke (increased to 90.7mm from 84mm), the motor's displacement was increased from 1997cc (2.0L) to 2157 cc (2.2L).
• Basically a 500rpm shift of the horsepower curve (to the left, on the rpm scale). Thus the new motor makes the same power as the older F20C, simply 500rpms sooner at basically every point on the curve.
• Compression has been bumped up a tenth of a point to 11.1 (from 11.0:1) and the valve timing has been altered to enhance mid-range performance.
• 240hp at 7800 rpm (vs 240hp@8300 rpm) and 162 lb-ft @ 6500 rpm (vs 153 lb-ft @ 7500 rpm).
• This will improve oil consumption and reduce piston noise, Honda improved the cylinder machine honing process by bolting a dummy head to the block (a technique used in race engine building) to improve accuracy. It results in reportedly less than 25% of the deformation on a block.
• The enlarged displacement results in a 6-10% improvement in horsepower and torque from 1000 to 8000 RPMs. Honda claims at the normal operating range of 4500 RPMs the 8 ft-lb torque increase in real world driving translates to 15 ft-lbs over the prior years engine.
• Continues to use traditional VETC instead of iVTEC as on the K-series motors.
• highway gas mileage dropped 1 mpg
• Honda claims better acceleration in each gear, offset only slightly by the reduced top speed potential in each gear (in the older car, thanks to the slightly taller gearing and extra rev capacity, you're able to hold a gear a bit longer, resulting in better acceleration during that brief period where the '04 must up shift while the '00-'03 is able to remain in the lower gear).
• Throttle pedal travel was shortened and pedal effort increased. By reducing the diameter of the throttle body drum, pedal effort is increased approximately 10% at the completely shut end, and 6% at WOT. This was done partly to reduce the occurrence of accidental throttle input such as when the driver encounters a road undulation. Accelerator pedal travel was shortened by approximately 10mm.
• The '03's pistons whiz at 4906 feet per minute at 8900 rpm, whereas the '04's slugs rip along at just 4761 feet per minute at 8000 rpm.
TRANSMISSION
• A tighter secondary gear reduction ratio (1.206 vs 1.16) to provide a bit more snap off the line and to better match the characteristics of the new motor. This is also called the intermediate ratio and is the gear after the transmission and before the driveshaft. It goes like this: Crankshaft --> clutch --> transmission (gears 1-6 + R) --> intermediate ratio gear --> driveshaft --> rear diff --> axles
• 4% shorter ratios for 1st through 4th gears while the 5th ratio is effectively 1% shorter and 6th is effectively 2% longer, for a slightly more relaxed cruise speed. 5th gear ratio changed from 0.971 to 0.942. 6th gear ratio changed from 0.811 to 0.763.
• Carbon fiber synchromesh replace the solid brass ones for all gears except reverse. The new design features a brass ring with a carbon fiber element bonded on the inner surface, resulting in simplified mechanical components, increased synchronizer capacity, improved abrasion resistance, and reduced weight. The weight reduction and increased capacity translates to a smoother and quicker shifting feel. Further enhancing shift feel quality is a reduction in the load acting on the disc spring. Per Honda, this tweak results in reduced shift **** operational load and reduced harshness.
• transmission case rigidity improved
CLUTCH
• Redesigned clutch and clutch case.
• To reduce the "impact torque" of a high rpm clutch dump, the new clutch has an additional orifice at the sleeve cylinder, which reduces the torque reaction acting on the drivetrain, in effect a clutch delay system.
• The clutch case has incorporated additional rib reinforcements to reduce vibrations and noises generated by the drivetrain. The additional ribs have improved clutch case rigidity by approximately 10%.
DIFFERENTIAL
• Redesigned differential; it has been beefed up.
• By moving to an FCD material (from FC), the case rigidity was improved by 40% while the overall case strength was increased 20%.
• Gear fatigue resistance improved by 5% through a change in the shot peening method for the drive pinion gear.
SUSPENSION & STEERING
• Front spring rates increased by nearly 7%
• Rear spring rates were softened by roughly 10%.
• Shock damper rates have been adjusted accordingly.
• Front stabilizer bar is unchanged.
• Rear stabilizer bar was reduced in diameter by 1.8mm to 25.4 mm to improve bump steer & cornering.
• To enhance steering feel and accuracy, the suspension geometry was altered slightly, lowering the steering knuckles by 1.5mm.
One owner’s research found the front suspension received a new front upper arm (left side only); some owner’s speculate that was to correct difficulties in setting the camber on that side. There’s a new part number for the self lock cam nut and bolt at the lower arm’s adjustment point. There’s a new part number for the front lower arm but no apparent geometry change; it’s thought to be a test spec. There are no apparent changes to the front sub frame. The rear suspension received a new knuckle and they moved the mounting point for the control arm. The bushing for the upper arm now has a separate part number; previously it bundled with the part. The tabs for the rear upper arm in rear sub frame have a new part number; it could be durability or geometry change. Front and rear hubs remain the same.
• The EPS (Electrical Power Steering) system features an optimized steer response gain, while the software was updated to improve steering linearity and agility. The steering gear ratio was also changed to match the new suspension and tire characteristics. Increased rigidity of the steering gearbox supporting mounts results in improved steering precision as well.
• One of the "features" of the outgoing S2000's rear suspension was its tendency to exhibit bump steer at the limits. Honda's engineers have attacked this issue from several angles. Rear toe in was reduced from -0deg 19' to -0deg 10'. At a 50mm bump deflection, toe-in has been reduced from -0.19 degrees to -0.05 degrees. Secondly, the rear roll center was lowered from 101mm to 92mm. Honda claims improved roadholding under full suspension compression or during severe body roll situations.
• Honda claims improvements in overall stability, steering accuracy/effort/feel, bump steer characteristics, wet performance/hydroplaning, high-speed stability, smooth ride comfort, choppy ride comfort, and at the limit controllability.
• steering wheel lock-to-lock increased from 2.4 to 2.6 wheel turns.
• steering ratio lowered from 13.8:1 to 14.9:1
CHASSIS
• Chassis code AP1 = MY00-MY03 chassis changed to AP2 with the re-designed bumpers and new headlights / tail lights.
• A new cross brace at the very front of the frame (positioned horizontally, in front of the radiator),
• Reinforcements at key crossmember joints
• Additional fixing points to existing braces
• Reinforcements to the rear wheel arch bulkhead
• Front suspension upper arm brackets were strengthened, further benefiting handling.
• overall weight increase of 25 pounds, from 2810 to 2835 pounds
WHEELS & TIRES
• New 17" wheels, wider in front and rear (by 0.5" and 1.0" respectively), wrapped in wider tires.
• In the front, 205/55R16s were replaced by 215/45R17 tires.
• In the rear, 245/40R17s bumped the incumbent 225/50R16s.
• HONDA says both changes are key contributors to extended cornering limits.
• The tires are now Bridgestone Potenza RE050s, replacing the former model's Bridgestone Potenza S-02s.
• The new tires feature a completely different tread pattern, intended to improve the balance in performance between dry and wet conditions.
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