BREAKING NEWS! The 56.0mm (+1mm Oversized) Pistons are here!
After many months of waiting, the 56.0 mm Cosworth/G-Force pistons are here. These pistons have been completely redesigned from the 57.0 mm pistons, with a new dome to maintain the higher compression with the smaller bore. As with the 57.0 mm pistons, these have been designed by one of the biggest names in Motorsports racing in the world. They are filled with the same design and manufacturing tricks you see in Formula-1, MotoGP and WSBK components. I have been working with Cosworth for motorcycle pistons for decades, and am most happy about these little gems.
These pistons were designed to increase compression, reduce reciprocating weight and friction in the running engine. They are a "Slipper" design, which has a smaller, narrower skirt to minimize the amount of skirt area that is rubbing against the cylinder walls - which causes friction. They are also sprayed with Xylan, the green skirt film that you see in the photos. This skirt film is designed to reduce friction, and help keep the noise down during cold running. Additionally, they are a 2-ring design to reduce the amount of friction caused by that 3rd ring. A warning, they do burn a bit more oil than a 3-ring piston, so you will have to check your oil frequently to see what you consumption level is.
In addition to friction reduction, the Slipper design also helps reduce weight by removing unnecessary skirt material. Cosworth also looks at every nook and cranny to see where they can safely remove weight to lighten the pistons even further. These pistons weigh 85.0g compared to the stock RVF piston's weight of 97.5g. Add the 3rd ring to the scale and you see the combined parts push right up to 99.6g. Round that to 100g, and the pistons lose 15g of reciprocating mass at 15,000rpm. However, the weight reduction doesn't stop there. The wrist pin was also shortened to make it stiffer as well as lighter. This brings the pin weight down to 24.8g from 29.0g. Another 4.2g of weight shed from this quickly moving set of parts. With the piston moving at 21 m/sec (4305 ft/min) at 14.750 rpm, that equates to a loss in force against the wrist pin, rod and rod bearing of 1239 Newtons (278.5 Pounds). This not only helps the engine accelerate faster, but live longer.
These pistons are designed to maximize the power of your engine by utilizing all of the combustion chamber space as possible. The squish has been tightened up slightly and the valve pockets are slightly raised to take up excess room. With that, I cannot stress enough:
YOU MUST CLAY THE ENGINE IN THE VALVE POCKETS AND SQUISH AREA!!!!!
If you do not, your engine could end up like one of ours:
When I said I have "Developed" these pistons, I meant it. This disaster was caused by me assuming that 1.5mm was enough Piston to Valve clearance on the exhaust. However, after tearing down this engine and diagnosing what happened, I apparently had the exhaust pockets 0.5mm too high. Therefore, what I though was safe (and the engineers at Cosworth concurred at the time) was actually not for our stock valve train. Now, after being able to see that the exhaust valves were just barely kissing the pistons (just enough to brush off the carbon, but not leave an imprint in the Aluminum) on the other cylinders that did not fail, I can tell you-with confidence- that the vales do float just under 2.0 mm at peak rpm.
The above carnage was with the Cosworth 57mm version 1 pistons. The 57mm version 2 pistons have been redesigned with valve pockets much closer to stock, and compression was found in other areas. Since the change to my mistaken assumption, there have been no other problems with the pistons. And, I have over 30 sets out there, all over the world. The 56mm piston dimensions are taken directly from the 57mm V2 pistons. So, I can say with confidence that they should drop in. But, that said, don't trust me. CLAY YOUR CLEARANCES!
You want the following clearances:
- 0.7mm ~ 0.8mm Squish Clearance measured at the sides of the dome just above the wrist pins (so piston rock does not influence your measurements)
- 1.2mm + INTAKE Piston to Valve Clearance
- 2.0mm + EXHAUST Piston to Valve Clearance.
Pistons: Cosworth 56.0mm v1/G-Force Design
Rings: Yamaha FZR400R STD size rings 1WG-11610-00-00 (Only uses the top ring and the oil control pack)
Bores: Stock Cast-Iron Liner - Bored to: 56.000mm to 56.020mm
Pin Height: Standard Length for 100.00 mm rod centers
Rods: Standard Rods acceptable. However, we highly recommend Carrillo "A-Beam, Sportsman" Rods
Compression: 12.35:1 or 13.90:1 with 0.5mm skimmed heads (e-mail me for shim kits as well)
Valves: Valve pockets enlarged on Inlet side only, for use with +1.0mm oversized valves. Exhaust pockets are stock size.
Gasket: OEM Honda. No modifications necessary
Max rpm: 15,000rpm
Expected Gains: Approximately 5hp throughout the power band - give or take, with proper tuning.
Cost: $1,550 without rings $1,700 with rings
There were only 12 sets of these pistons made. There are 4 spoken for, and there are only 8 left up for sale as of 27-Oct-2016. 4 are in the USA, and 4 in the UK. There will not be another order of these pistons - EVER. This is it. This your only and last chance to get these 400cc class-legal high-performance pistons in your little 400cc rocket. If you are interested, please contact me for further information at email@example.com if you are in the USA, or other than the U.K./Europe. If you are in the U.K. or Europe, contact Rick Oliver at firstname.lastname@example.org