Frequently Asked Questions

Yes. The second ring gap being larger then the top gap was an upgrade and improvement to a select number of our 4-Stroke ring packages. As the piston moves down on the power stroke, combustion pressure accumulates in the land area of the piston between the top ring and the second ring. This accumulation of pressure can cause the top ring to unseat from its sealing area at the bottom of the ring groove. This is addressed by increasing the gap area of the second ring. This affords a controlled release of the inter-land pressure, and keeps the top ring seated on its lower sealing surface for improved performance. Please remember this gap difference is not present on all of our ring packages, but just a select number of 4-Stroke applications.

Quality begins with a forging. Castings are porous and weak, Hypereutectic pistons are merely a cast piston with an increased silicon content. Although slightly better, they are not nearly as strong as forgings-which are pressed into shape with a 2000 ton press. Wiseco starts with certified extruded bar stock and forges our pistons in-house with the world's most advanced forging presses. Most aftermarket piston companies do not make their own forgings and therefore cannot achieve the level of quality control that Wiseco demands.

After thorough inspection, the parts go through an extensive heat-treat and finishing process. This creates an excellent forging with maximum strength and minimum variance. Another benefit to making our own forgings is the ease of making the finished piston design dedicated to your specific engine combination. Most companies buy one-size-fits-all forgings that require massive amounts of milling to create a useable part. These parts are heavy and are not nearly as strong as Wiseco Piston. Wiseco can forge a variety of advanced materials including S.A.E. 4032 and 2618 alloys. High silicon 4032 is a durable and lighter material usually used in naturally aspirated engines. 2618 Alloy is designed for the rigors of blown, marine, and nitrous applications.

The factors that affect this are cylinder wall thickness, whether the block is filled, the overall compression height of the piston, piston material and thickness, and whether a marine engine is to see fresh-water cooling. Most small blocks get .004 piston to wall clearance and most big blocks get .005 due to the use of our 2618 high-strength alloy. For heavy blower and nitrous applications, Wiseco recommends adding .001 to the standard clearance. Special note: Clearance numbers are obtained from measuring the largest diameter of the piston, typically at the bottom of the skirt. All measurements should be taken 90 degrees from the pin centerline.

There are many important factors, but the first two are bore size and compression height. Bore size is important for obvious reasons. Compression heights must vary due to the different block, stroke, and rod combinations. Compression height is the distance from the center of the wrist pin to the deck of the piston (not dome). When adding 1/2 the stroke + rod center to center length + Compression height, our goal is to have the piston with adequate piston to head clearance without being excessive (which causes a loss of compression and quench).

Rod material, the mass of the piston, and piston-speed are the factors that determine this. Steel rods in a big block usually require .045. Steel rods in small blocks require at least .036. Most imports can get by with as little as .030. Aluminum Rods generally require .010 more clearance than steel rods. *Remember, the compressed gasket thickness can vary from .025 in steel shim applications to .040 for composite and up to .100 for some copper gaskets.

The most important issue is to have a piston that is built for the right application. Material and thickness are the major factors. Street and drag race applications are fairly easy on pistons if ignition and fuel curves are correct. Circle track and road-race pistons see much on-off throttle usage and see more laps as well. Blower and Marine usage are equally as tough as marine engines can be under extreme load for extended periods. Finally nitrous applications are about the toughest environment a piston will ever see.

Wiseco makes super-light pistons for those people that are out to set records and are willing to check and replace pistons on a regular basis if needed. Wiseco's standard weight pistons are intended for use in endurance and other more abusive environments. If a blower or 300 horsepower of nitrous is to be used, please call Wiseco technical for specific recommendations. Always-Always use a timing control computer and have an adequate fuel supply when using Nitrous systems.

Compression ratio and Dome/Dish volume determine combustion efficiency and resistance to detonation. Detonation can and will destroy any piston in short order. Lean conditions will melt any piston as any aluminum alloy melts within a few degrees of each other. Most of a piston's heat is dissipated through its contact with the cylinder wall and oil splash. Very short pistons and excessive clearance will melt a piston sooner. Static compression varies more than most people would believe. A piston running .020 down in the cylinder at tdc as opposed to "zero-deck" on a 64cc combustion chamber headed 350 Chevy changes the compression ratio from 10.25:1 TO 9.8:1.

People running compression ratios higher than 14:1 are not making more power if it means an increase in dome rise. More dome rise only hurts combustion efficiency which will loose more power than is gained by increasing compression. The current trend in Pro Stock, Winston cup, and others with big-budgets for engine development is to make the combustion chamber smaller and go to 12, 14, or 18 degree heads to make that happen. They are going for the shortest dome rise that gives them the compression they are looking for. The trend is to also use a bigger bore with a shorter stroke to put an engine at its best power potential for a given cubic-inch limit. One point to remember is a pro engine builder will never trade ring-seal for cubic inches from making a cylinder wall too thin.

It is different for every different valve-train configuration, but depends more on cam timing and valve-train mass more than anything. Cam duration is the key; actual lift doesn't really come into effect, as the piston is half-way down the cylinder by the time the valve is at max-lift. The usual rule of thumb for an engine using rockers is .080 on the intake and .100 on the exhaust. The most common problem with broken valves comes not from lack of vertical clearance, but in fact a lack of radial clearance. Because of manufacturing variance in the cylinder heads, a piston must to be built with a valve pocket that is larger than is needed. Always clay or use other steps to measure clearance around the edge of the valve. Most of the time measuring one cylinder is not enough as a problem can start at one end of the engine and get progressively worse down the length of the engine.

This scenario is interesting because it brings up almost all of the unusual problems that can occur when building a stroker motor. A flat top of minimal crown thickness would be needed to accommodate the thick "small-end" of an aluminum rod. This compression ratio requires a 55cc dish-which is not possible. In addition, ring land thickness would be well below Wiseco minimum standards. Always call your Wiseco representative first before designing a large stroker combination that may be impossible to build a piston for.

Whenever it is necessary to put the wrist pin bore into the oil-ring groove, it is necessary to keep the oil ring end gaps from rotating and falling into the open pin bore. Wiseco developed and uses a dimpled spacer. The spacer is installed first with the dimple down in the pin bore to keep it from rotating. This method is far superior to buttons in every aspect.

The Anti-detonation grooves prevent carbon-buildup from locking up the top ring. They also help keep the air and fuel in suspension. The accumulation of gases that get by the top ring can unseat it. A pressure groove delays this action. This is why today's recommendation is to keep the 2nd ring end-gap as large or larger than the top ring end-gap.

Compression ratio is the volume of the cylinder when the piston is at the bottom of the cylinder compared to where it is when the piston is at TDC. A 100 cubic inch cylinder would have its volume squeezed into 10 cubic inches with a 10:1 ratio. The easiest way to keep track of it is to think of every thing as volumes that are stacked on top of one another. The factors that stack up are the displacement of the cylinder (bore and stroke), the volume of the deck clearance (getting back to the zero-deck issue from before), the volume of the gasket (which is basically a short-round cylinder), and the volume of the combustion chamber. The net combustion chamber volume means you must subtract dome volume add the dish volume. Use the formula (bore x bore x stroke x .7854 x 16.4) to get the volume for a cylinder in cc's. Stack up the cylinder + the deck volume + the gasket volume + the net chamber volume---take this number and call it A…Stack up the deck, the gasket, and the net chamber volume and call it B….. Take the big number A and divide it by the small number B and it will give you the compression ratio.

Ring packages almost always consist of 3 rings these days. If ring life is not a concern, the .043-.043-3mm is common. For people looking for better performance with longer life, run the Wiseco GFX Ring package. The GFX rings have a stainless steel Gas nitrided top ring with a Napier hook second ring and nitrided oil ring rails. The GFX rings are a .047-.047-3mm size. The most common long life ring package for 4-inch and over bore is a 1/16, 1/16, 3/16. Dikes rings are currently only popular in blown alcohol or Top Fuel applications. Gas ports should be added when using the extra-thin ring packages. Important note: It is the customer's responsibility, when using a .043 ring-pack, to specify when a back-cut (Pro) ring is used versus a standard (D-wall) ring.

Vertical gas ports are primarily used in drag race applications. Lateral gas ports are more often used in circle-track and road-race applications where carbon build up can occur. When gas ports are used, pressure is directed to build up behind the compression ring and seal it against the cylinder wall. This helps prevent ring flutter and extends the power curve upward in the RPM range. Vertical gas ports have the holes drilled from the deck of the piston into the top ring groove and behind the ring. Lateral gas ports are drilled through the bottom side of the top land and extend to the back wall of the ring groove.

A full FAQ page for our EFI Controllers can be found in PDF form on our installation manual page or by clicking HERE.