Our recent testdrive of the '08 Corvette (Apr. '08) yielded a torrent of technical questions concerning one key subject: How was Chevrolet able to make significant improvements to the decade-old LS engine and offer the result as standard fare on the new Vette? For answers, we contacted John Rydzewski, Assistant Chief Engineer, Passenger Car Small-Block Engines at GM Powertrain. In a wide-ranging interview, Rydzewski filled us in on the history, development, and construction of the Chevy's latest small-block dynamo.
Vette: When was the LS3 engine designed, and how is it related to the LS7?
The LS3's enlarged pistons...
The LS3's enlarged pistons feature a number of refinements aimed at improving their suitability for high-rpm and competition use.
John Rydzewski: The LS3 and LS7 share a common background. The LS7 was released in May 2005, and I believe we went after the machining of the heads a year before that. At that time [2004], we had a head that was developed that we called "the big head." It was produced for our truck motors [RPO Code L92], and that same head casting was also used for the LS3.
Vette: Why did you choose this "big head" for the LS3?
JR: It was an opportunity to get more performance out of the LS3, and it was an opportunity to deliver the same value to the customer. The big head proved successful on our truck motors, and it was the right thing to do to offer it as part of a new engine for the Corvette.
While a larger (4.06-inch)...
While a larger (4.06-inch) bore may be the LS3 block's most notable change, there are other, more subtle modifications. Refinements to the block casting, for example, yielded a 20-percent increase in strength as compared with the LS2.
Vette: How is the LS3 cylinder head similar to the LS7 unit? How does it differ?
JR: We had the big head pretty much as-is cast on the LS7, [but] we went the next step on the LS7 where we CNC-machined the intake and exhaust ports and the combustion system. We put a lot of extra machining processes into the big head to deliver the LS7 engine, and we did get a lot out of that. However, we took another path for the LS3 since it is a high-volume application. We went after conventional as-is casting of the cylinder head, and that's where the two heads differ.
Vette: How does the LS3 valvetrain improve on the components fitted to the LS2?
JR: Valvetrain-wise, we have a larger intake valve on the LS3 cylinder heads, [but] we didn't want to compromise the limiting speed of the engine. Being a larger valve, it had more mass. We actually had to go to a hollow valve on the intake, and that was basically to get the mass equal at higher speeds.
Straighter, larger-volume...
Straighter, larger-volume intake ports, meanwhile, offer a whopping 17-percent increase in airflow.
Vette: What testing was performed on the LS3 cylinder heads to provide data GM engineers could use to facilitate airflow improvements?
JR: The engineers tested these heads through simulation, on our airflow bench, and went out onto the track with some local race groups to collect data. We were surprised how much data we actually achieved that way.
Vette: Were you pleased with the airflow improvements manufactured into the production LS3 cylinder heads?
JR: There's good improvement comparing the LS3 heads to the older LS2 units. We achieved a 17-percent increase of airflow on the intake side and a 6.2-percent increase of airflow on the exhaust side. The results are pretty significant.
The cylinder heads used on...
The cylinder heads used on the LS3 are structurally similar to the LS7 Z06 and L92 truck units. Redesigned exhaust ports offer a 6.2-percent increase in airflow over the LS2 apertures.
Vette: How does the LS3 aluminum block differ from that of the LS2?
JR: There's a different diameter for the bore. The 364ci LS2 is a 4.00-inch bore, and the 376ci LS3 is a 4.06-inch bore. Because we have a higher-output engine with the LS3, the other area we had to go after was improving some of the structure in the block. One of the areas that we focused on was the bulkheads. We used our analysis group, which is really state-of-the-art in this corporation, and they have some techniques on how to change some of the contours of the casting. Basically, the solution was to make one of the radiuses a bit gentler at the bottom of the bore, and [they] found another 20 percent of structure by doing this. That was the critical area for performance.
Vette: How did you improve upon the rotating assembly of the LS3 compared with the components engineered for the LS2?
JR: We did much work on oil control in the piston design and added some features [to reduce] oil consumption. Basically, four drilled oil-drainback holes were put into the piston. We also optimized the ring pack and the angles of the grooves in the piston and the profile of the rings. That was another area we focused quite a bit on, and we were able to come up with a piston system that works very well with track usage.