Engine Tech, Building the Nissan VG30DETT part 1

The Rods

Rods are a critical part of the motor.  Because they tether the pistons, which move up and down with considerable force to the crank, the rods are the most highly stressed part of the engine.  A rod failure is very catastrophic, usually destroying the entire engine.  Although the stock forged steel, bronzed-bushed, floating wrist pin, Nissan rods are very strong and really are like many companies’ racing rods, we opted to go to an improved real racing rod for our peace of mind.  The stock rods are very strong and have been used in 600 hp engines with no problem before but the cost of failure is so high, we do not want to take any chances.

Our Cunningham rods are a work of art.  Here they are hung with our JWT pistons.

We selected  Cunningham rods for our motor.  Cunningham rods are forged from billet, then machined to final shape.  Most high performance rods are simply machined from billets of high quality steel.  Cunningham actually forges the rods to near net shape, and then machines the forged blank to final dimensions.  This forging process improves the grain structure making it finer and also aligns the metals grain in the correct orientation with the direction of stress.  This means that the grain is aligned with the length of the rod.  Cunningham uses 4340 high nickel aircraft chrome moly to make their forging blanks out of.  4340 is much tougher than regular steel and is typically used in racing crankshafts, rods and drivetrain parts.  The rod’s critical bolts are machined from high strength H11 tool steel.  The bolts can take an incredible 296,000 psi of stress before breaking.  This is a substantial advantage because most rod failures are directly attributed to the bolts breaking.

This forging results in a part that is much tougher and lighter than a part that is simply cut from billet.  Cunningham also uses a two piece forging die so the rods cap has the grain flowing around the rod’s bore.  Cunningham is the only rod company to do this.  This helps keep the bore from distorting under load and can help improve rod bearing life.

Cunningham rods are machined to very tight tolerances, so tight that it is nearly impossible to see the parting line between the cap and the rod body.  Every bearing bore is consistent down to 0.0001” and all rods are the same weight down to within one gram making balancing unnecessary.

Our rod with one of our pistons and a set of rings.

The rods are also shotpeened with a special two step process that uses two different sizes of shot at different velocities with a post peening non-directional polishing process.  This intensive shotpeening and polishing operation increases fatigue strength an additional 20% over regular shotpeening.

Finally, the rods are over 100 grams each lighter than the stock rods, reducing reciprocating weight and additional strain on the rotating parts of the engine.  These factors added up will give us a quite a bit of insurance against engine failure, money well spent we think.