Pop the hood of an ’02 and this is what you see: nothing different on the outside. Lots different on the inside, though. Image: Author. Click Images for Larger View

New Catalytic Converters The day before my run up GMR, I sat down with Dave Hill, Sam Winegarden, GM Powertrain (GMPT) Division Chief Engineer for Small-Block V8s and "Doctor" John Juriga, GMPT’s Assistant Chief Engineer for Gen III Passenger Car Engines, to talk about LS6 for ’02. Almost the first thing Hill said answers claims advanced by some conspiracy theorists that GM delays engine performance increases to enhance marketing.

John Juriga (at left) and Dave Hill brief the motoring press on the LS6 engine revisions during the ’02 Z06 press conference at Irwindale Speedway on May 10th, 2001.  Image: Author. Click Images for Larger View

"We never set out to obsolete the 2001 (LS6)" Hill said. "The horsepower increase was possible only after we completed a lengthy development of a new catalyst. I want to set the record straight: the 2001 was the best Z06 we could possibly make and 2002 is better because new catalyst technology let us get the back-pressure down, increase the breathing and make that power increase."

Sam Winegarden gave the C5 Registry On-Line and the C5 Registry Newsletter a similar opinion,"To be bluntly honest with you, we weren’t quite ready. There were some valvetrain issues we needed to work on. Reducing the mass of the valves and working with the aggressive ramp rates on the cam were challenging. There were other challenges, obviously, but I think the valvetrain was the trickiest to get solved and balanced. We’re not going to do this thing if we don’t have a quality solution in hand. Not having resolved those issues in the final weeks before '01 production, we agreed to do it as a two step process, ’01 and ’02. So it was purely a case of when we were ready. We’re still not selling wine here before it’s time." "A lot of the increase stems from the exhaust system–the catalytic converters," John Juriga added. "In 2000, we had to meet the LEV (low emissions vehicle) here in California, so we added close-coupled convertors up front (of the regular cats) on the California package–our "pups" as we call ’em.

’02 LS6 vs.’01. Below about 3750 rpm there is no practical difference between the two but get on the loud pedal and let the motor rev through 4000 rpm and, trust me; you’ll feel the difference. Chart: GM Powertrain Division. Click Images for Larger View

Here’s the ’02 LS6 and ’02 LS1 compared. Again, up to 3750 or so, the two engines are very close, but get to four grand and, whoa, you’ll be gettin’ some serious religion with the LS6. Chart: GM Powertrain Division. Click Images for Larger View

"A lot of the increase stems from the exhaust system–the catalytic converters," John Juriga added. "In 2000, we had to meet the LEV (low emissions vehicle) here in California, so we added close-coupled convertors up front (of the regular cats) on the California package–our "pups" as we call ’em. "In 2001 we carried those pups across-the-board. Even while we were implementing that, we were working on a design that would eliminate the pups. This reduced back-pressure by two inches of mercury. On its own, that was worth about 5hp. That seems not much but, if you reduce back-pressure by even small amounts; you can make a bigger gain with improvements on the induction side, especially with the cam."   The "under-floor" catalytic converters (aka "catalysts" or "cats") on a C5 have been the same since model year 1997 (MY97). Cats must sustain a high interior temperature for the catalytic reaction necessary for the conversion of exhaust pollutants to occur. The period of time after engine start but before exhaust temperature gets high enough for the cat to begin working or "light-off" is always difficult from an exhaust emissions standpoint.

To meet LEV for MY00 and keep Corvette saleable in California, Juriga’s team of engineers had to make cat light-off happen sooner. The solution for ’00 California cars and all ’01s, because LEV went nationwide at that point, was to move the catalytic reaction closer to the exhaust heat by adding small, close-coupled, catalytic convertors or "pup cats" upstream of the under-floor cats, near the exhaust manifolds. While the official ratings did not change, ’00 cars with pups were about 5hp short of the ’97s, ’98s and ’99s. MY01 had no loss because LS1 was changed in other areas negating the pups’ effects.

Engineers call the interior structure or substrate of a catalytic converter a "brick" because of its characteristic shape. The ’97-’01 under-floor cat used a single brick having palladium and rhodium as the reactive ingredients. The ’02 cat is a two-brick design. The front brick uses palladium and the rear brick uses a platinum-rhodium combination. This new cat, along with some changes in PCM calibration, allows the LS6 to meet LEV without pup cats and their exhaust back-pressure. There were other benefits, too. Going pupless means less cost and a 5.5lb. weight reduction.

Air Flow Enhancements: Next