The Last Hurrah

Also from Issue 30

  • Milford Proving Grounds visit
  • History: Two-Rotor Corvette
  • C4 pickup truck
  • Market Report: C5
  • History: 1958-59 design
  • Racing: GT1 title tightens
  • How-To: TPI fuel injection rebuild
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Amazingly, this three-way “synchronous en­gineering” scheme went pretty smoothly, ultimately saving the program time and catching several pot­entially major hassles before they became irreversible. GM and other carmakers embarked on a rash of similar group projects in the wake of the Chevy/Lotus/MM experiment, but few of those turned out to run nearly as smoothly.

While engine development progressed the rest of the C4 had to be prepped to accept the new high-output V8, which had been designated LT5. Many of the pieces needed already existed, such as ZF’s six-speed manual gearbox and (with minor geometry changes) the current C4 suspension. The most obvious change was adding very wide rear tires, which McLellan hoped would give all the extra pow­er some prayer of reaching the ground. To cover this rubber, the bodywork was widened three inches at the rear via subtle swelling that began at the doors.

When the ZR1 debuted in the fall of 1989 the press couldn’t rave enough about its silky-smooth, tire-smoking LT5, which debuted with 130 more horses than the smallblock L98. Although the price of the ZR1 option was over $27,000 above and beyond the base Corvette, there was no question the result was a rival for superexotics costing three times as much.

Yet even as the accolades poured in, two groups of GM employees were doing a slow burn over the LT5/ZR1: smallblock-devoted engineers and dollar-obsessed beancounters. The latter were ticked because no matter how they sliced it, the LT5 was prohibitively costly. There was absolutely no way it could ever be widely affordable—and, as such, GM could never make it a viable long-term solution. That meant embarking on yet another new engine program, leaving the whole LT5 adventure one big financial black hole.

As for the former, Chevy’s venerable thinwall V8 had grown from 265 cid to over 400 with time, but in production form it had failed to kick out more than 250-odd net bhp—a lot less than many engineers felt was possible. Tired of watching from the sidelines, this camp set out to completely re-think GM’s traditional pushrod V8 (it was the first time anyone had seriously questioned its fundamentals since the early ’50s). The team saw that—glamorous or not—the bone-simple two-valve V8 offered big advantages in cost, weight, assembly time, packaging ease, and reliability potential. If LT5 levels of power could even be ap­proached with the simpler engine, it would be a huge coup for the whole Corv­ette program.

Spearheaded by Anil Kulkarni, this group tackled the most pressing of the old smallblock’s problems, namely spot cooling—the ability to maintain workable temperatures at key points around the combustion chambers. They realized that reversing the coolant flow would help lower piston and head temperatures, which in turn allowed them to release more energy with each revolution. That breakthrough, together with ongoing advances in fuel delivery, ignition, sensor technology, and valvetrain geometry, let the aging pushrod en­gine leap up to 300 horsepower, with more waiting in the wings. Further research indicated that redesigned heads, a beefed-up lower end, and improved fuel delivery could bring the figure to then-current LT5 levels.