Ruthless Pursuit of Power: Our In-Depth Look at the 2008 Corvette LS3 Engine - Page 2 of 6

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Ruthless Pursuit of Power: 2008 Edition - Page 2 of 6

Our In-Depth Look at the New 2008 Corvette LS3 Engine

© 2007 by Hib Halverson
No use without permission, All Rights Reserved

In the Spring of '07, we visited GMPT's World Headquarters in Pontiac, Michigan to interview John Rydzewski, Assistant Chief Engineer for Small-Block Passenger Car Engines. Rydzewski leads the team of engineers working Corvette engines and the first subject we breached was the increased block strength.

Click image for larger view For Corvette engine geeks, this is the Mother Ship, where most of the engine engineering is done--GM Powertrain's World Headquarters in Pontiac, Michigan. Image:  Author	Click image for larger view John Rydzewski is a Corvette engine ace, both figuratively and, as he's the LS3's Assistant Chief Engineer, literally. Rydzewski worked on Small-Block as far back as 1993 and he's been ACE since 2005. Image:  Author

"When the block is honed, the bottom of the honing tool needs clearance so it doesn't contact the block below the bore." Rydzewski told the Corvette Action Center. "Before the honing operation, the block is machined in that area to provide (hone over-travel) clearance. The resulting surface geometry has a big impact on the block structure. The hone over-travel clearance used to be machined with a 3-mm radius. With LS7, to get more strength in that area, we changed to a more gentle, 8-mm radius. That was a big durability enabler at the LS7's power level. When we got into the LS3 finite element analysis (FEA), we found our safety factor needed some improvement, so we applied what we learned about LS7's hone over-travel cut-out. We were able to increase the radius to 10-mm which was worth about a 20% improvement (compared with the LS2 and '07 L92 blocks) in the strength of the block structure in that area."

LS3's nodular iron, rolled-fillet-journal crankshaft is similar to LS1/2/6 parts except for counter weights altered to rebalance the engine for a slightly heavier piston.

The shotpeened, powdered metal, hot-forged, steel connecting rods are the same as what was in LS2 except for a new rod bolt. Rod length remains 6.1-in. The rods are "net shape" so post-production machine work for balancing is not required. As before, they're "cracked rods" which means that, to simplify manufacturing and enhance fit between rod and cap, the big end is fractured in half rather than machined. The rods' small ends are bushed for full-floating wrist pins.

Click image for larger view Rods with cracked or "fracture-split" big ends are common on modern engines. The fracturing creates a unique interface that "locks" together only one way and does so very precisely. The more accurate interface ensures a uniform big end diameter and shape. Image:  Author	Click image for larger view Starting with the LS2, Gen 4 V8s use a full-floating wrist pin so the rods are silicon-bronze bushed and the bushing has an oil feed groove milled into it. Image:  Author	Click image for larger view The LS3 rod bolt uses two different thread sizes and diameters to control and localize bolt stretch. Image:  Author.

The new rod bolt is made of stronger material and meets the same grade 12.9 specification as do LS7 bolts. The better material allows clamp load at the rod cap interface to go from 47 kilonewtons to 50kN. The design of the rod bolt was changed, too. ""An alignment feature was added to the shank of the fastener," John Rydzewski told us, "and unique threads are rolled into a short length of the shank.

"An (old style) connecting rod bolt will have deformation along the length of the fastener which results in concentrated stress at the first engaged thread. Since unengaged bolt threads are able to stretch freely while engaged threads are constrained by the threads in the rod, the first engaged threads are more highly stressed

"The new Small Block bolt is similar to a 'necked-down' fastener, where the bolt stretch/deformation will be focused in a portion of the length of the bolt not near the first thread of engagement. Compared to the standard threads (on the rest of the new style bolts, this area has) a larger outer diameter which provides alignment to the rod hole and they have a smaller minor diameter which provides an additional benefit of isolating much of the plastic deformation from yield to this rolled section of the fastener. Therefore, the concentrated stresses at the first thread of engagement will be less and the overall joint safety factor improves."