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Technical Section

Piston Features | Machining Options & Codes | Installation Instructions


Piston Features

Cam-milled Side Reliefs
The Venolia special profile is designed to remove excess weight from the piston, without sacrificing reliability - it's one of the most critical operations in piston manufacturing. The milling cutter follows the contours of the master and works in much the same way as a cam grinder.
Cam-milled side reliefs are standard on some Venolia pistons, optional for others.

piston side reliefs

Pin Buttons
Venolia's wrist pin buttons provide positive pin retention in pistons. In replacing pin locks, these buttons are used to support the oil rings when the oil ring must be in the pinhole on engines with large strokes.

pin button

Power Slots
Plug reliefs and power slots are essential for maximum performance in certain applications. In engine types where the dome of the piston blocks the flame front-travel or makes contact with the plugs, reliefs are necessary. Tests have indicated that power can be increased significantly by putting in a large relief for facilitate proper flame travel.

power slots

Snap Locks
Truarc's and Spiralox's double snap rings are recommended for all racing applications where pin buttons are not desirable.

snap locks


chevy 350 piston

Venolia Chevy 350 Piston

Machining Options

Maximum Weight Removal
Maximum weight removal utilizes every weight removing operation that is available. These processes provide the lightest piston for specialized use and are recommended especially for super stock and modified drag racing applications.

piston weight removal

Angle Pin Oilers
The oil pick-up holes is located in the oil ring land and is large enough to allow more than adequate flow. The openings connect with the pinhole allowing for full pin lubrication. The oiler system is not recommended on some applications (inquire before ordering).

angled pin oilers

Plunge Valve Reliefs
Venolia has created special tooling to faithfully duplicate the underside of valves in the piston relief. The pocket matches the shape of the valve head.

[note: Particular care should be taken when ordering tuliped valves, as many engines are produced with a variety of valve head shapes. Furthermore, tuliped valve reliefs can affect flow in the chamber]

plunge valve reliefs

Vertical Gas Ports
Gas ports allow cylinder pressure to pass directly behind the top ring and aid sealing ability. Cylinder pressure no longer flows past ring sides, thus preventing ring flutter and loss of compression.

vertical gas ports

Lateral Gas Ports
Gas ports allow cylinder pressure to pass directly behind the top ring to seal the ring. This option is required with minimum side clearance.

lateral gas ports


Codes for Optional Machining Operations.


Pin Fit


Internal Skirt Milling


Oil Squirt Notch


Internal Head Milling


Mill Pin Boss Width


Plunge Pin Boss


Machine Bottom Pin Boss


Chamfer Pin Boss


Angle Pin Oilers


Bottom Pin Oilers (4)


Plunge Valve Reliefs


Vertical Gas Ports (11 holes)


Lateral Gas Ports


Hardtuf® Coating (nitro)


Skirt Coating


Thermal Barrier Crown


Piston Rework/Shop Time, per hour (1 hour min.)


Pin Shortening


Offset Pin Hole


Contact Reduction Grooves


Accumulator Groove


Maximum Weight Removal Combo (3 items)


Dome Mapping/Trace Profile - Set-up Fee
(not required with job card on file)



Installation Instructions

  1. The cleaner your bores, the better. For best results:

    a) Thoroughly wash the block with a spray solvent gun.

    b) Wash thoroughly with soap and water.

    c) Using a can of spray oil (like WD-40®) and a roll of paper towels, spray all the bores and allow to sit for a few minutes.

    d) Carefully wipe each bore with a clean paper towel. Check each towel to determine if there are any metal particles still left in the pores of the bore. The light oil will float the particles out of the pores. If the towel comes out dirty, keep repeating the process until the towels come out clean.

    PISTON CLEARANCE: With 2618 alloy, top of skirt .008 to .010. Bottom of skirt: .005 to .007". Air cooled engines usually require more clearance.
  2. Check your pistons completely for any burrs or sharp edges. Using a deburring knife, lightly go over any sharp edges. Make sure there are no chips in the ring lands and pin locks left from machining operations. Thoroughly clean the pistons in solvent and blow them dry with a high-powered air hose.
  3. Check all rings in their respective bores for proper end gap clearance. It is best to use a ring squaring tool to make sure the rings are square in the bore before measuring end gaps. Make sure you use a commercial ring filer to increase the end gaps and that it cuts the rings square.

    RING CLEARANCE: Side Clearance .003 to .004 ring gap: .004 to .005 per inch of bore.

    When fitting rings to cylinder bores, every .001" change in bore diameter changes the end gap by approximately .003." Diameter changes affect the gap by the factor of Pi 3.1416. An example of an increase in bore diameter of .002" increases the ring gap by .00628.
    Example: .002 x 3.1416 = .00628
  4. Install the rings on the pistons with a commercial ring installer to prevent damage to the rings. Place the end gaps at 90 to 180 degree intervals. It is best to place the top end gaps toward the torquing side of the piston.
  5. Check for piston to valve clearance. This can be done by placing modeling clay on the piston domes and installing the heads and valve train and then rotating the engine. Remove the heads and check the clay thickness. It can also be accomplished with lightweight 'checking springs' that are available from many camshaft manufacturers.
  6. Have your block ultrasonically tested for cylinder wall thickness. On cast iron blocks, .150" is the absolute minimum.
  7. Make sure the deck surface has been machined flat and smooth. If the engine is a V-8, the decks must be equal distance from the crank centerline and the decks 90 degrees to each other. Use torque plates that exactly duplicate head distortion.
  8. Install the main caps and torque them to specs for all boring and honing operations.



piston dome height
compression and block height
ring widths
deck clearance rod length

piston orientation

Replacement pistons for V-8 Chevy and Chrysler motors.

Cylinders 1, 4, 5 and 8 are LEFT PISTONS and have exhaust valve pockets on the left side.

Cylinders 2, 3, 6 and 7 are RIGHT PISTONS and have exhaust pockets on the right side.

note: 90° V-6 motors require 4 left and 2 right pistons.



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