Pistons

I guess you would agree with us, there is something magical about pistons! The shape, the alloy, the details, the specifications and the precision make us petrolheds drooling over them! As a matter of fact, it is nicer to have them in the storage compartment than inside the engine. Then you can open up the box now and then, take a sneak peek at the gorgeous pieces, and of course brag about them to your buddies.

CP Carillo, www.cp-carrillo.com has made our pistons! We have chosen CP Carillo because they have very good references. Customer service is excellent, and the final product is absolutely flawless!  We store several complete kits of these pistons for future V12 builds.

Preferred piston qualities

You may ask if there is anything special about the pistons that we have ordered for our engines? Basically, like any other custom piston, they are designed spesifically to serve the needs of our engine. When that is said, we had some preferances when we started  designing the pistons together with CPs engineering team. First of all, it is very important to emphasize that we are not making race engines! Reliability and longevity is highly prioritized, and therefore we looked very closely at how BMW had designed their pistons. First of all, as you may be able to see from the pictures, we like "skirt" around the piston to get better stabilization, and we have basically copied the manufacturer's design. A larger, or longer skirt area, will also prevent "scuffing", which can often be a problem where the piston has less guidance in the cylinder bore. The pistons are forged, and made from 2618-T61 Alloy. This is commonly used as a piston alloy, and especially in high cylinder pressure / high performance applications. The 2618-T61 alloy is of a low silica content material, which makes it stronger and more durable than the more brittle 4032 alloy, used in some piston forgings. This type of forgings have a higher content of silica, making them less affected by heat. However, because of the low content of silica in the 2618-T61, this alloy will be more affected by the heat and will make the piston expand more during heating. This has to be taken into account when designing the piston to the specific cylinder bore. For the curious, the cylinder bore in our engines is 85,00 mm, / 3,346 Inch. The turn diameter of the pistons is 84,94 mm, / 3,344 Inch.

Features

When diving into the world of pistons, one will soon realize that there is a lot to learn in this field as well. You can specify and customize your piston to make it fit excactly to your engine's needs. There are many different options to choose from that can make your piston a better one. We have selected a few options that we believe our engines will benefit from, especially when it comes to durability and longevity. Below, you can read about the features we that have chosen.

Accumulator groove

CP has machined a V-shaped groove in the second ring land that adds to the volume between the top ring and the second ring. This groove accumulates residual gasses from combustion which alleviates top ring flutter and premature second ring wear, improving ring seal.

Anti detonation grooves

Also known as contact reduction grooves, which limit the piston to cylinder contact during high temperature and high RPM.These grooves also protect the top ring by disrupting detonation waves.

Broaches 

Broaches are horizontal slots in the pinbore designed to allow oil to enter between the wristpin and pinbore. Broaches are also used to accomodate the wristpin shape under compression, and it can become somwhat oval and needs room in order to alliviate galling.

Wrist pin

The wrist pin in this case is of the heavy duty type. My good friend Jack Kane, the CEO of at EPI Inc. www.epi-eng.com told me that we should pay attention when it came to selecting this little piece of steel rod. High combustion pressures over time can have a bad effect on wrist pins, and fatigue has sometimes occured. The wrist pins we are using are made of 9310 alloy, with 6,35 mm / 0,250 Inch wall thickness. The thicker walls will obviously make the wrist pin heavier, but since we are operating under relatively moderate engine RPM, this will not be an issue.

Skirt coating

Our piston skirts are coated with a CT-3 Dry Film Lubricant Coating. This type of coating will help reduce scuffing, friction and adhesive wear. It is used primarily to coat piston skirts, provides intermittent dry lubricant and is not affected by dust or dirt. CT-3 should be used in combination with a lubricating oil, grease or paste. The CT-3 coating is applied as a spray process. Different surface preparatory methods appropriate for the substrates are used prior to the coating process. Coating thickness is varied to suit the application. Typical coating thickness for piston skirts is 12 to 37 microns.

Some advantages of the CT-3 coating is:

• Low Coefficient of Friction
• Corrotion Protection
• Chemical Resistance  

Heavy duty 9310 Alloy wrist pin, 6,3 mm / 0,250 Inch wall thickness

Compression ratio is 8,0 : 1 

CT-3 Dry Film Lubricant skirt coating

Piston rings

The piston rings that come with each piston are especially designed to run against the NicaSil coated cylinders in the engine block.

• The 1,2 mm top ring is a steel compression ring that has been gas nitrided so that it is compatible with NicaSil and cast iron bores. This scuff resistant gas nitrided ring allows it to operate at maximum efficency without blemishing up the bore. The nitriding ensures extended life and protection under extreme conditions.
• The 1,2 mm second ring is a cast iron ring with a taper underhook groove face. This ring acts as a wiper and pushes the oil back away from combustion. This type of ring allows one to run a lower tension oil ring.
• The 2,0 mm oil ring kit is made of two gas nitride rail with a low-tension expander. Because of what CP calls the "miniflex" vent design, there is less friction on the cylinder wall, which increases the performance and efficiency of the engine.

These ring sets are high strenght and low tension, resulting in maximum sealing with minimum drag.