There is no question that the Speed Pro and old TRW forged pistons are solid and reliable. They are stable and will take a lot of abuse. Literally millions of them have been put into service through the years. At one time they were the only forged pistons that were readily available for many engines. My gripe with them is mainly in two areas, weight and recently, cost.

The 318 piston/pin in the picture weighs 767 grams, according to the scale. Stock weight of a 318 piston is 591 grams. Stock weight of the pin is something like 170 grams. So the piston is a stock replacement weight.

Mopar pistons and connecting rods were nothing if they weren't heavy. The 720 gram 340 piston is my prime example. That's without pin. Another example is the LA's 645 connecting rod. At 758 grams, it is fat. Even the early 318 skinny rods were 726 grams. It isn't hard to buy a new rod at least 100 grams lighter. If you look you can shave off 150 grams per rod.

In Mark's Mechanical Engineering Handbook in the Automobile section I first ran across the concept that at a certain gear ratio it takes as much power to accelerate the engine rotating parts plus rotating parts of the drivetrain as it takes to accelerate the entire mass of the vehicle.

This puts a new light on rotating mass.

R.