Cosworth Piston Engineers - Sport Compact Car Magazine

Each technician works in a clean workbench cubicle during assembly. Cosworth's in-house machine shop builds all the specialized tools and jigs to ensure streamlined and consistent assembly.

Each technician works in a clean workbench cubicle during assembly. Cosworth's in-house ma

The process begins with the tearing down of a stock VQ35DE core motor. All we're interested in is the block casting and ancillary hardware. As standard practice at Cosworth, the block and parts are cleaned in an ultrasonic solvent tank, dried, and de-burred of rough edges and casting flash that can act as stress risers. Edges inside the crankcase-as well as the block's external features-are ground down by hand to avoid potential failure points. At the same time, the machine shop builds a deck plate specifically for this engine and the bore it will receive.

The deck plate is bolted to the block during boring and honing, to simulate load on the block when the head is in place. And Cosworth doesn't hone by using a dingo-berry brush on a hand drill. Each cylinder is first machined to 0.004 of an inch of its target dimension. The rest of the material is machine-honed with a diamond cutter to within 0.0001 of an inch of the specified bore. The honing machine not only ensures trueness of the cylinder walls, but also moves up and down in a consistent motion for even material removal. Final plateau honing is done with a brush tool that doesn't remove material, but knocks off microscopic ridges from the previous hone and reduces wall roughness.

Each ring is leveled at a set height in the cylinder with more custom-machined tools and measured for the proper ring gap clearances. Our high-rpm motor will run thinner rings under less tension for reduced flutter and friction.

Each ring is leveled at a set height in the cylinder with more custom-machined tools and m

At the bottom, Cosworth decided to stroke the motor by 6mm to 87.4mm with a new custom crank machined from billet steel. Since it's a development prototype for the production piece, the crank won't get the mirror-finish micropolish found on Cosworth's other production cranks. This micropolish adds additional surface hardness, as well as some stress relief. Even though our engine is destined for dyno use only, Cosworth has the crank fully counterweighted to compensate for the harmonics of the V-6 configuration. Knife-edging has been omitted, since we plan to use a dry-sump oil delivery system, which eliminates any windage losses. Rotating mass will be taken out of the more significant components like the rods and pistons.

Unlike Nismo high-compression motors, where a smaller combustion chamber cast into the head increases compression, Cosworth chose to alter the ratio strictly through the piston profile. This allows off-the-shelf Cosworth high-flow CNC heads to be used with either NA or boosted applications. Our higher 12.5:1 forged aluminum pistons (for 100-octane street gas) were also one-off development units specifically designed and machined for this challenge.

Come assembly time, Cosworth uses sleeves machined to the exact cylinder bore to install each piston and rod. The tapered sleeve gives a more precise fit and prevents potential damage to the rings, cylinder, and deck during installation.
Come assembly time, Cosworth uses sleeves machined to the exact cylinder bore to install e

The Cosworth CNC cylinder heads are machined from brand-new OEM castings. CNC machining are used to machine out each port and combustion chamber to an exact profile. This ensures that each combustion chamber and port is identical to the next. Notice the precise knife-edge on the port divider inside the port, and notches from each cutting pass.
The Cosworth CNC cylinder heads are machined from brand-new OEM castings. CNC machining ar
The combustion chamber is smoothed of unnecessary valve and spark plug reliefs that can act as localized hot spots and cause detonation or flow restrictions as air enters and leaves the chamber. Larger stainless steel and Inconel intake and exhaust valves are also used.
The combustion chamber is smoothed of unnecessary valve and spark plug reliefs that can ac

These multi-barrel profile pistons are lighter than production units to increase the rev limit, but still feature the same polished face, patented friction-reducing anti-contact/anti-detonation bands in the first ring-land and a blow-by accumulator groove in the second ring land as Cosworth's production VQ pistons. Where ours differ is mostly in weight and durability. Since our application is NA, Cosworth saved more weight with thinner piston-face thickness (compared to turbo pistons), which affect strength against combustion pressures.

Many piston manufacturers take one generic design and only alter the face machining to change compression for boosted or NA applications. Cosworth's piston engineers design unique or net forgings with different face thicknesses, side profiles, skirt designs, and ring placement appropriate for the application. Our dyno-use pistons also feature shorter slipper skirts strengthened with more structural gussets for less weight, less friction, and higher revs. Thinner rings for less flutter were specced out for the high speeds this motor will be spinning at. We're also using less ring tension, since oil scavenging isn't an issue with a dry sump, plus non-offset wristpins compared to the production offset slugs.