Originally Posted by JRP

The LS1 uses a sintered, forged, PF1159M steel connecting rod. Also called "powdered metal" or "PM," this technology was introduced in Corvettes for MY96. The basic, Small-Block rod currently in the GM Performance Parts catalog is also PM.

To make a sintered rod, a mold is filled with steel powder which is "briquetted" or compressed under extremely high pressure. Then, the rod is "sintered" which heats the metal just to its softening point causing the steel molecules bond and making a dense, very strong part. Next, the rod is put through a conventional forging process. Lastly, it is shotpeened. The combination of these manufacturing techniques results in a rod with "net shape," which requires no machining for profile or balance and is more consistent in mass than rods of traditional manufacture.

The LS1 rod is also known as a "cracked rod" because the big-end is fracture split. During the finishing process, to split the big-end; a stress riser is cut into its inside diameter. The rod is stressed such that it fractures at that riser. The jagged surface left on both pieces precisely locates and locks the rod cap in place once the rod is assembled. For simple assembly and mass reduction, the LS1 rods use a 9 mm. capscrew rather than a rod bolt and nut to hold the big-end together.

Rod length is 6.1 in., .400-in more than the LT1/4 rod. The extra rod length reduces rod angularity and piston speed which decreases friction and noise and increases durability. LS1 rods have no balance pads making for less overall mass and allowing the engine to rev quicker. Undoubtedly you're asking, "Hey, wadaya mean 'no balance pads.'? How do they balance the rods, then?"

Well, they don't.

Small-Block rods were held to a weight tolerance of ±5 grams, per end, after balancing. The LS1's PM rods are manufactured to a tolerance of ±3 grams for the small end and ±4g for the big end without machining for balance. Such are the advantages of a net shape.

How good is this connecting rod? Many stock rod Small-Blocks, after lengthy time in severe duty, will display fretting corrosion of the inside diameter of the big end. This is due to the big end flexing a tiny bit under the bearing shell. The LS1 rod, under similar operating conditions, shows virtually no fretting. Bottom line: The LS1 rod is the strongest connecting rod ever used in a GM, production, mid-displacement V8.

The new engine has of cast aluminum pistons. Their compression height is 34mm and they weigh 434 grams each. Unlike production Small-Block pistons, they have no steel reinforcement strut. The old engine needed that feature to control piston expansion because the manufacturing process controls used previously and bore distortion due to the old engine's having head bolts threaded into the block decks, made for wide variation in bore sizes. To keep piston-to-bore clearance such that acceptable durability would come even with the smallest, expected bore size; piston expansion had to be restricted and that was done with the steel reinforcement.

With the Gen III engine family, process controls at the block machining stage are tighter and there is no bore distortion due to head bolts because their threads are very deep in the block. With bore variation significantly reduced, piston expansion control is not an issue, so the steel strut was eliminated making for a lighter piston that is less costly to manufacture.

The biggest visual differences between pistons for the new engine and those for LT1/4s are 1) LS1 units have no valve reliefs, 2) they have 6mm. less compression height which allowed the longer connecting rod and 3) the top ring was moved up 1.5mm.

There is a ton of technology in piston and rings aimed at reducing friction. The rings use the same basic materials as before but the design is different. The LS1 top and second rings have 1.5mm faces vs. the 2.0mm rings used in LT1/4. The tension of all rings have been reduced by about 30%. Reduction in ring face widths and tension would never have proven reliable from a cylinder sealing and oil consumption standpoint, if process control improvements did not result in reduced bore variation and improved consistency in individual bore diameters.

The LS1's pistons are lighter than a LT1/4 piston. A bore size 2.5mm smaller, 6mm less compression height and the lack of a steel strut make this possible. Improvements in LS1 rods and pistons have reduced the weight of each rod/piston assembly by 120 grams compared to the same LT4 pieces. That is a significant decrease that guarantees the engine will rev quicker (and it does!!) and be more durable at high engine speeds

Originally Posted by redrocketls1

im doing a compression test soon.. think ive hurt the pistons... if it comes back bad i need to know what pistons to order to replace them and what else ill need.. if someone could tell me that it'd be a big help thats for sure! hell it maybe alright.. 50/50