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 feature a number of refinements aimed at improving their suitab
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 , 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) bore may be the LS3 block's most notable change, there are othe
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 intake ports, meanwhile, offer a whopping 17-percent increase in
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 LS3 are structurally similar to the LS7 Z06 and L92 truck u
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.
The LS3's hollow-stem intake valves (right) measure 2.16 inches in diameter. The LS2 used
Vette: What challenges did you overcome to increase the horsepower of the LS3 while also improving engine life?
JR: The block was one of the challenges that we went after, and we had to resolve it using analysis tools. That was very successful. Another area was the rod-joint capability-the rod bolts. We had to improve that entire joint. We went after a redesign of the bolt-or rather, a change in the materials of the rod bolt-to a higher-grade bolt very similar to what we use on the LS7. That was an area [where] we actually ran many component tests to verify we were capable of running at high speeds and high loads for a prolonged amount of time-something that's very important to the people who take these engines and cars out on the track. It was a challenge to go after that!
In addition to its larger intake valve, the LS3 head (right) also gets reshaped combustion
Vette: When you designed the LS3, was your horsepower target purposely weighed against the classic 427/430 L88 motor?
JR: No, we didn't purposely compare the horsepower of the LS3 to the plateau reached by the classic Chevy big-block motor. We looked at our competitors of today and where they are, and where our platform needed to be from a performance level. The Corvette is class leading, but we wanted to increase that lead.
Vette: Did computer technology at GM change sufficiently between the development of the LS2 and the development of the LS3 so that you were able to increase performance as a result?
JR: Our standards of what we look at and what we try to do have changed quite a bit. Our capability has become very good. Pretty much every month we have new techniques that improve our capability for analysis.
While enhanced performance was the chief goal of the LS3 program, improvements in refineme
Vette: Did you design the LS3 with future modifications in mind, so enthusiasts can easily add horsepower?
JR: There's always room for improvement, so enthusiasts can do things, whether it's [reducing] induction-system restriction or exhaust restrictions. As I mentioned, you can polish these cylinder heads or take them out to a porter and do some work on the intake ports and the exhaust ports and get toward an LS7 in performance. There are camshaft options out there, too, that can get you more performance. What we put together is a good balance. It gives you emissions capability, fuel efficiency, and much more performance [than the LS2]. It's a quieter application, too. We've added some features for refinement, but someone who wants to actually go out and increase the performance of the LS3 has a lot of capability to do that.
Vette: How do you feel about power adders on the LS3 to elevate its horsepower output to supercar status?
JR: We expect it. Many of our buyers do quite a lot of things to our vehicles and take them on tracks and enjoy their performance, and we get good feedback that way. There are many aftermarket performance parts out there, and we expect our customers to do things like that.
GM Powertrain's John Rydzewski poses with a cutaway version of the LS3.
Vette: How do you feel about the LS3 being carbureted for hard-core race use?
JR: Wow, this is the first time I've been asked that question. If it works, if someone wants to do it, I don't have a problem with it. It's a big change; you'd have to change the intake manifold and fuel system, [but] that certainly is a possibility. I'm sure there are people out there that will do something like that.
Vette: What do you see in the future of the LS3?
JR: We're looking at all kinds of technology. We definitely can't sit still, because the competitors aren't sitting still. We have to focus on many of the regulations out there, [including] emissions. Fuel efficiency is one of the most important things customers want right now, but we want to deliver the class-leading performance along the way, too.