How to Prep a C5 Corvette for Racing

The C5 Corvette has never been an egregiously expensive car and, fortunately, the current pricing hasn’t changed much. With minimal investment, the C5 Corvette, which was built from model year 1997 to 2004, will morph into a capable racecar, and the ceiling is almost unlimited. Aftermarket support for this car makes the move into multiple categories simple and stress-free, and the incredible potential of the LS engine platform gives a wide range of power options. That might be the car’s greatest strength, but not just because it’s powerful. Easily attained power improves the C5’s versatility and operating costs.

Good aerodynamics — the glass hatchback is better than the fixed-roof coupe of the Z06 — lots of torque, superior suspension geometry, a low center of gravity, near 50/50 weight balance, and a traction-aiding transaxle indicate a design aimed at racing. It should be described as a car with good bones, but the C5’s final execution suggests Chevrolet had to make compromises along the way. Things such as proper fluid cooling, adequate oil pressure, and dependable braking have to be addressed by owners if they aim to take their C5 racing.

“The C5 Corvette was designed to be a racecar. It’s clear it was built to go fast, but without some vital upgrades, the fun won’t last long,” says Scott Blair, ST3 Mid-Atlantic racer.

Regardless of whatever category it is raced in, C5 owners must address several failure points and build around some of the car’s limitations. Do this correctly, and the car will be stout and safe enough for sanctioned competition. Unlike some of its rivals, it can be done very cheaply, too.

Non-Negotiables

• Unless the owner is interested in replacing the OEM wheel bearings and hubs every season, he or she ought to try the heavy-duty SKF replacements, which should last five years or more.
• Cooling from the factory is sub-par for racing. To race the car, a larger radiator, an oil cooler, a transmission cooler, and a differential cooler are essential.
• Stock brakes are not adequate for much more than casual lapping days. Bigger front brakes and brake ducts are necessary for anything more.
• The cabin is tight and may limit ingress/egress with a full containment seat, so those who need a little more room to get in and out of the car should run triangular nets on either side, and might consider a halo-less seat.
• Early versions of the LS6 valve springs suffered some failures, and the operating experience is well documented online. Swapping to LS3 spec or one of the many aftermarket valve spring options is an easy fix.

Non-Essentials

• Wide front tires place some strain on the factory power-steering pump, which may not be up to the task long-term. Turn One’s power-steering pumps and improved cooling will avoid an embarrassing mid-lap failure. The C5 cannot be driven without some assistance.
• The stock rubber suspension bushings should be replaced with delrin or monoballs. This will allow for less static camber.
• The rubber couplings at either end of the torque tube will fail and cause collateral damage. Avoid catastrophic damage with poly or solid couplers.
• ABS systems in the ’99 to ’04 cars perform the best, and the updated version from ’01 to ’04 is the cheapest to fix. These later modules can be retrofitted to an earlier car with some work.

Limited Lubrication

Both factory lumps are reliable, lightweight, and make good power. However, their oiling systems aren’t adequate for high-G loading, and the oil levels can overwhelm the LS6’s PCV system

“Oil can accumulate in the heads due to sustained high-RPM operation, hence the reduced diameter push rods some use, or some people also modify the lifter trays by drilling holes in them to help oil drain back to the sump faster. If you have sustained high revs, you have more flow-rate through the PCV system and it can entrain too much vaporized oil in the flow,” said Ben Grambau, an ST2 C5 racer. For this reason, a catch can with a wet-sump oiling system is a must. Lastly, like with any of the LS engines, it’s wise to overfill by a quart.

One way in which the LS6 shines above the others is that its broad, shallow “batwing” oil pan is sufficient for track use — provided slicks and wings aren’t used. Go beyond that, and you’ll need something more helpful.

At this stage, there are a few cost-effective options: do nothing, upgrade the pan’s baffling, or add an Accusump. “If you want cheap peace of mind, go for an Accusump,” says John Nguyen, founder of the burgeoning Spec Corvette series.

Start Simple

Some prefer to keep their C5 basic. Nguyen wanted a silhouette-style racer that was capable of fast times without spending a lot on tires, brakes, and aerodynamics.

To try to limit spending and emphasize the driver element, Spec Corvette uses near-stock C5s with a few modifications to run in close competition at reasonable costs. The car runs on a durable 200-treadwear Nankang tire, and the only aero element is a 3-inch ducktail spoiler from Trackspec. To give it a greater sense of urgency, the spec car wears a reasonably-priced set of one-way Penske 8300 shocks and replaces the factory rubber bushings with monoballs.

“Nothing changes the feel and response of the car as much as getting rid of that factory rubber,” says Grambau.

Even with the horsepower and it’s not-inconsiderable weight of 3,200 pounds, a Spec Corvette isn’t that hard on consumables. A set of Nankang NS2Rs can last three weekends, and if you opt for the recommended Wilwood six-piston brakes, a great budget option, its rotors will last a year, and pads can last six weekends and still provide front-running performance. Retain the stock brakes and you’ll be working on them a lot of the weekend, but the stopping power is sufficient. Best of all, a front-running Spec Corvette can be built with all new components for about $40,000 — quite inexpensive for the lap times it can turn.

Regardless of whether the donor car is powered by an LS1 or an LS6, it shouldn’t have much difficulty making the maximum 380 rear-wheel horsepower per the Spec Corvette rules. To keep things simple, there are a few easy ways to make that power.

According to the regulations, the LS6 only needs to retain the factory headers, but everything behind that is open. The LS1 needs to borrow the intake manifold, heads and camshafts from the LS6 to make the necessary power, or, as the rules stipulate, if the LS1 is kept factory, a set of long-tube headers are allowed. Best of all, these mildly modified powertrains can handle a few years of competition without issue.

Stepping Into ST

Lots of displacement and 380 horsepower means the car has the straight-line speed to match more expensive cars. That alone is such an advantage when it comes to climbing the racing ladder. In fact, Greg Nester entered his Spec Corvette in ST3 at the NASA Championships last year and finished third. Interestingly, the car ran in full Spec Corvette trim, with no aero or slick tires. To be fair, the Spec Corvette was suited to the track and the conditions.

“We have less drag without wings, so we tend to do well at the power tracks,” Nguyen notes. Plus, the slippery conditions suited the Nankangs on Nester’s car. At tracks that do not favor horsepower, the C5 requires a little more aerodynamic grip than what the Spec Corvette offers.

“Aero and race tires are a big requirement if you’re going to be competitive in ST3 and ST2, as with most any NASA ST class. A good chassis-mounted wing and splitter are all that is needed to be competitive, though, of course, things like flat floors and diffusers can give an additional edge,” Blair said.

One can take a clean-sheet approach if one so chooses. Blair’s jump into ST3 came after he wanted to race something faster than his GTS2 E36 M3 that he had loved and campaigned for years. After learning more about the C5 platform from friend and fellow racer Ben Grambau, he realized that he could go a lot faster for a little more money. Sure, the Corvette would not run consistently on stock brakes and without oil coolers like the M3 would, but that beautiful sounding V8 motor opened up a whole new realm of possibility.

As any half-awake racer knows, it’s cheaper to buy an existing racecar than to build one. Blair wanted to save himself the headache of doing the basic work, and he craved something simple, thoughtfully prepared, and relatively light. He settled on a ’99 FRC race car with minor performance modifications, and the basic foundation proved itself the first weekend out.

Blair’s elation atop the podium that Sunday confirmed the C5 was the right way forward, and his enthusiasm spurred him to start looking for the next few modifications to find an edge. Sadly, his joy did not last long, and after just three events, the LS6 let go. The combination of low oil pressure in high-G corners, and excessive blow-by meant it was time for a replacement motor.

The modularity of the LS motors powering several different variants of the C5 and C6 gives the C5 owner the chance to retrofit this car easily. With healthy examples of used LS1 and LS6 motors getting harder to find, the best bargain for big power is arguably the 6.2-liter LS3 motor, which can be purchased brand new from GM in several variants.

More Power, More Seat Time

Blair could have sourced another LS6 for less, but he took the opportunity to install a new factory GM LS3 crate motor, mainly for one reason.

He wanted to be able to fit into two different classes, depending on where the car counts were highest. Having the necessary average rwhp at a weight of 3,200 pounds makes it easy for a C5 Z06 to fit into ST2 at 8:1 without crazy mods to add power or reduce weight, so he sought out an engine that would do that easily.

The crate LS3 comes in three variants, so Blair chose the version making 525 horsepower, thinking that detuning as is necessary for ST3 and ST2 would lengthen its life. With the ability to reflash the ECU, courtesy of HP Tuners, this version of the LS3 allowed him to alternate between ST3 and ST2 power levels.

Versatile, straightforward, and ubiquitous, the LS3 will make life easier for most, but it requires a few pieces to swap, and the costs cannot be ignored.

An LS3 swapped C5 will require owners to swap to an LS3 intake manifold, fuel rail and a “silver blade” LS2 throttle body, because the gold blade LS3 throttle body is not compatible with a stock C5 ECU. Additionally, you’ll need a few wiring harness adapters and sensors, which include a crank and cam sensor trigger wheel converter box, a MAP sensor extension, knock sensor extensions, and, depending on your intake and engine tune setup, a MAF sensor adapter. These swaps have been well documented and the prospect of one should not cause any worry.

The financial problem with an LS3 swap is not the immediate cost of a crate engine, nor the ancillaries. The LS3’s oiling system is slightly worse than the marginal LS1/6 oiling system, and it needs an expensive dry-sump system to support it on-track, especially if wings and DOT R-comps are involved. Blair saved thousands by piecing together an ARE dry-sump and building it himself. Still, the cost to swap in a new LS3 crate motor with a dry-sump can fall between $12,000 and $20,000.

A Thin Line 

Now, with the exception of the stiffer penalty in ST3 for a sequential transmission, the main difference between ST3 and ST2 versions of the C5 is power — all else can stay the same. At a competition weight of 3,200 pounds, the ST3 car at 10:1 can make 320 wheel horsepower, and the ST2 car at 8:1 can make 400 wheel horsepower.

The additional power does make a noticeable difference in straight-line speed, the driving experience, and the bill at the end of the season. A driver must pay more attention to putting power down with an ST2-spec car, and the additional straight-line speed increases the consumable costs somewhat.

Mixed Drag

The C5’s svelte shape and its big motor are its greatest assets against ST competition. Even against slippery Porsche Cup cars, the C5 has a serious advantage down straights. This is a large part of why front-running ST2 racers are willing to spend upward of $10,000 to get the best aero packages available and expend considerable effort installing them.

Whether you’re running ST3 or ST2, good aerodynamic grip is necessary to compete. You’ll need a square set of 315mm wide Hoosiers, a 72-inch rear wing, and stiffer springs to support the aero loading. You’ll also need a 4-inch splitter, which takes a surprising amount of work, especially if it needs to be removed easily to load/unload from a trailer.

“Adding a splitter to the C5 isn’t as straightforward as other model year Corvettes,” notes Jim Tway of Tway Motorsports. Among the cognoscenti, the C5 is referred to as a bottom-feeder, which refers to how it manages the air entering from underneath the front bumper. In stock configuration, there’s an air dam mounted at the bottom of the radiator and perpendicular to the road’s surface. This meets the air head-on and forces air into the radiator core at a 90-degree angle.

This imperfect design works decently until a splitter with an undertray is fitted. Then, the airflow must be gathered from elsewhere, and a laydown-style radiator must be fitted.

“Once the splitter and undertray are in place, we have to route air into the radiator through the front bumper. This can be accomplished by either adding a World Challenge-style front bumper with an integrated opening, or grabbing a tool and opening up the stock bumper and fitting a custom fabricated duct,” Tway stated.

“We also have to improve cooling and aerodynamic capability, which means changing the radiator orientation from its OEM upright position to a laydown orientation.” Laying the radiator down will also require the air intake to be routed under a headlight to grab fresh air.”

An unfortunate side effect of adding a front splitter and modifying the air flow through the radiator, is that it leaves the air with nowhere to escape. Regardless of radiator orientation, drivers taking their stock C5 to the track for the first time might be startled to see their car’s hood bulging from the unrelieved air pressure concentrating underneath. Therefore, plenty of hood venting is a must.

ST2/ST3 Versus Spec Corvette

It’s hard to make sense of the spending landscape when first looking at the C5 and all the ways it can be modified. The Spec Corvette package is aimed at low running costs, moderate cornering speeds, and large, competitive fields. Roughly 75 percent of the platform’s potential can be enjoyed with minimal expense. The Spec Corvette and lower-end ST3 builds provide this amount of performance for relatively little money — somewhere around $35,000 to $40,000.

It should be noted that the ST2/ST3 price range varies wildly. An ST2/ST3 Corvette can run as high as $100,000. Of course, a Spec Corvette will not come close to a no-expense-spared ST2/ST3 build, but at a typical regional race weekend, a Spec Corvette remains competitive with most ST3 entries with aero and Hoosiers.

Full ST2/ST3 C5 Build Options:

• 320-400 horsepower from a detuned and dry-sump engine.
• Full aero, 72-inch rear wing, 4-inch front splitter with tunnels, and canards.
• AP Racing front and rear brake kit.
• Triple-adjustable Penske or Ohlins coilovers.
• Significant chassis lightening via carbon body panels, Lexan windshield, stripped chassis, unnecessary wiring removed.
• Option to add widebody fenders and increase tire size (335 or 345).
• Upgraded TR6060 transmission or a close-ratio sequential gearbox for ST2.
• Lightweight 7.25-inch clutch allowed 50 percent weight reduction.
• Upgraded limited slip differential.
• Bosch Motorsports or Teves MK60 ABS systems.
• Aftermarket ECU such as Motec, Haltech, AEM.

Whereas a Spec Corvette Runs: 

• 380 horsepower, no dry sump.
• Duckbill spoiler.
• Standard MN6 or MN12 Z06 gear ratio.
• LS7 clutch, stock differential, and stock ABS.

Consider these costs and compare them to an equivalent E46 build. This is considerably cheaper than an E46 running at the front of the same pack, but the Corvette’s weight, power, and footprint all add to the running costs.

Going beyond that point requires an exponential hike in costs — nearly tripling with some ST1 builds. Still, it’s far cheaper than building a top-flight Porsche or BMW.

For that reason, it’s best to avoid the temptation of a bargain Corvette that’s a little rough around the edges. The entry costs of a nice C5 will still be considerably less than a comparable BMW, and provided the car’s driven well, the entry costs of a nice C5 are considerably less than a comparable BMW — and provided the car’s driven well, it’s just as fast, if not faster.

The C5 was designed to go quickly, but it needs a bit of assistance when the owner aims to jump into the fastest club racing categories. At the lower levels, it’s fast, fun, and much cheaper than a comparable BMW.

That addictive powerplant comes at a cost, though. As the owner climbs into faster categories, the expensive dry sumps and tires make themselves felt. Even so, the C5, even in its fastest guises, is versatile and supported by a wide aftermarket, so building one is never venturing into unknown territory. It might require a hefty check, but at least the build won’t require forum scouring or exotic parts.

The C5 might not have the feel or precision of certain rivals, but its remarkable straight-line speed, supportive aftermarket, and straightforward operation more than outweigh its shortcomings.