One Step Beyond - April 2006 Corvette Magazine

[6 Shooter]

One Step Beyond

The 2006 Z06 has barely been with us a few months, and already buyers and tuners are figuring out what comes next. Nick and George wanted to know how the industry is planning to beat the last word.

Tweaking. Hotrodding. Tuning. Whatever you call it, the art of modifying cars is as old as the car itself. Even in today's high-tech environment of sensors, multiple processors, and central computers, developing post-factory upgrades is big business.

While many tuners have been able to keep up with the ever-changing state of the OEM art, the hotrodding road certainly gets tougher to navigate every year. The sheer complexity of the systems involved constantly grows, as do the legal and financial limits on what shops feel they can try to do. But there's another problem now looming on the horizon, and it's one very few hotrodders ever contemplated: New cars may be getting too good.

The 2006 Corvette Z06 is the best example to date. With over 500 bhp, flow characteristics on par with the best hand-massaged motors, and displacement approaching that of the biggest musclecars, it's tough to imagine where even greater performance might come from. The Corvette Z06 is in essence already a tunercar: 2.2-inch titanium intake valves, a souped-up cam with 0.591 inches of lift, forged titanium rods, dry-sump oiling, and solenoid-opened exhausts are really the kinds of things that Corvette shops—indeed high-end race shops—would have turned to themselves. This time, it's been-there, done-that.

True, thanks to the awesome performance right out of the box, most owners will leave their LS7s alone. But tuning isn't really about having more power; it's about having more power than the next guy. No matter how strong the car's starting point is, speeds shops are there to help owners go beyond that.

In preparation for the inevitable desire for more Z06 speed, aftermarket-tuning firms were contemplating mods long before the car made it to showrooms. Though most of these companies were confident that speed parts could be developed and sold for the car, until the engine reached private hands few would guess what they were likely to be. Would the usual hotrodding tweaks that were successful on the earlier, less aggressively built LS engines work on the new LS7?

In a word, yes.
They think.

Most of the tuners we talked to are still in the early stages of their Z06 projects, but every team is optimistic about its basic chances. Without exception, they all believe useful, bolt-on LS7 upgrades will be a reality by summer '06.

At its most fundamental, the real question for each tuner is whether to approach the LS7 as an already-hotrodded version of the LS2 or as an entirely new and different engine. While subscribing to the first notion quickly curtails the options, the second view gives them an all-new starting point for ever-loftier achievements. Guess which they all chose.

Nor is this argument purely semantic: Even though common sense and the spec sheet suggest the LS7 is simply an already-worked-over LS2, the relationship between these engines isn't so clear-cut in practice. By the time GM Powertrain gathers up all the new pieces and hand-assembles them at its Wixom Performance Build Center virtually no crossover remains between the two mills. Instead of thinking of the LS7 as an LS2 minus the low-hanging fruit, there's no fundamental reason not to treat it like a brand-new tree.

 

[6 Shooter]

As of presstime the Z06 has only been in dealerships a few months, so development time in the speed industry has been minimal. Nonetheless, almost every firm we talked to has already been tinkering with the LS7's Powertrain Control Module, flow-testing its cylinder heads, and experimenting with different cam profiles. Clearly, the race to become the first C6 Z06 supertuner is on.

Of all of the tweaking processes, cracking the electronic code of the PCM is widely considered the most pressing. "Nobody's got anything for the computer yet," Rick Hollenback, of Synergy Motorsports in Fremont CA, explains. "That's the biggest drawback right now. [GM] changed the computer so radically that we've got nothing to work with."

Doug Rippie of Doug Rippie Motorsports, Buffalo MN, agrees. "We're waiting until the computer issue gets solved. General Motors makes it harder and harder to get inside these things, but I estimate that we'll have something in a couple of months."

Rippie, like Houston-based tuner Motorsport Technologies Inc, uses an outside electronics firm to handle the bulk of the computer dissection. "I wish I had more information," MTI's Jayson Cohen says ruefully. "We've really been on hold with the Z06, [since] we like to wait until the software is available before we do anything else. It makes the entire package come together. Sure, you could take a brand-new Z06 and bolt on a cam and a set of headers: If you can deal with a flashing check-engine light in your $70,000 car, that's fine. But I can't do that with a customer's car. Besides, having the right software will be absolutely critical for dialing the car in correctly, [just as] it was absolutely critical on the LS2."

Even though a reverse-engineered understanding of the new PCM is still a way off in the future, it doesn't take more than a few dyno pulls to reveal the fundamental nature of the factory's program. "The stock software is very conservative," Cohen confirms. "We dyno-tested one and found that the PCM pulls a lot of the timing as the engine warms up. We were putting something in the 450-horsepower range to the ground when it was cold, but it dropped into the high 430s when it warmed up. If you were at the dragstrip the car would run great cold, then start slowing down after a pass or two." Varying the ignition timing based on engine temp is nothing new, but the range with the LS7 seems to far exceed that of earlier LS-series V8s. "On the LS1, once the engine started drawing in hotter air the PCM could retract anywhere from one to about four or five degrees of total advance. The LS7 maxes out at 11.5 degrees."

Hollenback has experienced similar results on his own dyno. "They went extremely conservative on the tune. They run the timing real low and dump in a rich mixture. They just played it very safely. Bear in mind, they've gotta keep the thing safe so they can say 'here's a warranty' with a straight face." Hollenback is optimistic that simply applying more aggressive computer code to an otherwise stock LS7 will yield noticeable results. "I think the LS7 will realize larger gains from the same kinds of tweaks we applied to the older LS motors. On an LS2 I'm used to seeing 12- to 25-horsepower gains from a [computer] tune on a stock car. With the LS7, I don't see why 30 shouldn't be possible right off the bat."

A fully programmable PCM may be a hangup right now, but few think it's that far off. "God didn't make that computer," says Rippie. "We'll be in there soon."

Once the electronics are under control, some tuners think the next step will be to simply apply the same techniques that have worked on their earlier LS builds. Others are hardly so sure: One of the main sources of previous LS gains has been cylinder-head cleanup, they point out, and the LS7 already has exceptionally efficient performance there. "The heads are flowing wonderfully," confirms Hollenback. "We're talking 360-plus CFM at .600 cam lift. Half of the aftermarket stuff out there can't even touch it. It's awesome."

MTI's Cohen has found the same thing. "That head just wants to run—it never stops flowing. We've run it up to something like .750 lift and it never backs up."

 

[6 Shooter]

Rippie, who's offered heavily massaged LS heads seemingly forever, adds that, "...these heads flow just as well as some of our ported LS6 heads." But that doesn't necessarily mean the tuners have hit a wall. Maybe, says Rippie, the factory heads are just the opposite. "I think they'll just mean larger gains from upgrades like cams and exhaust systems. And hey, even though the heads flow so well, we'll be able to find a way to clean them up more."

Because Cohen received an early set of LS7 heads MTI was already testing them on the flow bench while most other tuners had yet to see their first car. "A production cylinder head that flows between 360 and 370 is really phenomenal," he says. "Even so, we changed the valve job and saw a 20-cfm improvement right away. We have our own specific angles that we cut on the valve seat and the valve itself, and that makes a dramatic improvement on the intake when the valve cracks off the seat. I don't think they're putting the best valve job possible on at the factory."

While most tuners are guardedly optimistic about finding improvements on the intake side, they're downright anxious about tackling the exhaust side. Rick Hollenback at Synergy again: "The only bad part about these heads is that they didn't do much on the exhaust. That's probably the most obvious area for improvement."

Cohen, who's had more time to test and experiment on the units, agrees with the problem but isn't so sanguine about the solution. MTI discovered early on that the original 2.2-inch intake valve was more than adequate but that "...the exhaust didn't flow so well." On closer inspection, it appeared that "...when [GM] moved the valves apart in the chamber to make room for that 2.2-inch intake valve, they shoved the exhaust valve way over into the wall. By doing so, when the exhaust valve extends down to allow the gas to flow out, it's heavily shrouded against the edge of the chamber. There's really not a whole lot you can do [to change that]; the chamber is already cut to match the cylinder-bore size. We just don't see a lot of room. We've spent a lot of time looking at the exhaust ports, and we think the biggest restriction is the location of the valve itself. We're still doing tests." Is the situation hopeless, then? "I think it may be possible that we'd improve the flow by going with a smaller exhaust valve and doing the right valve job on it, but I can not tell you that with accuracy."

While the flow-bench crowd keeps mining for gold in the top end, others are getting excited about work further down in the block. The OE camshaft is hardly a shrinking violet, with atypically fast and high lift for a street unit. All the same, the factory setup must still do a difficult balancing act between performance, efficiency, driveability, and emissions. Any aftermarket cam grinder willing to gamble away some of the last three elements should in theory find more of the first.

The factory grind features almost .600 inches of lift—which is a lot for a streetbound production car—but Rippie says there's plenty of latitude left over. "The stock lift is nice, but the duration isn't there. [They say] a cam is no good without cylinder heads; conversely, since the LS7 heads flow so well just as they are, they can easily accommodate a more serious cam. Plus there's lots of piston-to-valve clearance. It's as if Chevrolet was just saying 'here you go—put in a big cam.'"

Cohen echoes that thought. "The cam isn't even coming close to taking full advantage of that intake flow. Going with higher lift won't be a problem because the heads can accommodate it. You've also got that 12-degree valve angle, and the flatter the valve is to the piston surface the better piston-to-valve clearance you're going to have. And I'd expect to see big changes to the duration as well. Even if you're trying to keep an emissions-legal car, I still think there's room for improvement."

Rippie and Cohen both see the OE valve springs as this engine's potential Achilles heel, and both note this problem will only be exacerbated by installing a hotter cam. "[Upgrading the valve springs] is almost mandatory," Cohen warns. "Even if I had a stock Z06 I'd be extremely nervous about those. I'd want some performance aftermarket springs that aren't going to break and drop a valve."

Programmable PCMs and more aggressive cams are hardly the only routes for LS7 modification, but until these are sorted out there may be little incentive to start trying other tweaks. All of the usual bolt-ons, from cold-air intakes up front to wider exhaust tips in back, will find their way onto the new Z06, but to make those thing really matter requires solving the first things first. Right now, tuners are only seeing the tip of the LS7 iceberg, and everything else is speculation. Speculation, however, is part of what moves tuning forward. "I don't know if anyone is going to make a header for the Z06," is Cohen's example. "The exhaust that's already on there is pretty damn good. An LS2 header will bolt up fine, but I'm not sure it will be correct for the ports and the angle of the exhaust flow."

Despite the seven-liter displacement, Rippie wonders if there are additional cubes yet to be found. "There's always something that can be done there. The first thing we'd look at is putting a stroker crank in it, maybe something like 4.125 inches. I haven't looked at the block yet but I bet we could bore that .020- or .030-over as well. That would make something like 445 cubic inches."

Hollenback, still eagerly awaiting his hot-wired PCM, recently did a few dyno runs with various LS-series bolt-ons in place just for fun. "We got a basic idea of air/fuel, and then we stuck on a set of LG headers and pulled out the air filter. It pulled almost 500 horses at the wheels just like that—there's definitely a lot that can still be done here."

Those are encouraging words, especially in light of the LS7's initial strength. But after the dyno rollers come to a halt, what will the owners of these cars be left with? Could Rippie, Cohen, Hollenback, and the rest be pushing the car past the point it should really go?

Probably yes and no. In part, those concerns can be answered with money. "People are already commenting on the brakes," Rippie notes. "I don't know why the factory has not addressed that, but either way it's good for us. We're going to offer 15-inch rotors with six-piston calipers." The Corvette-tuning industry knows that whatever the problem may be, solutions are there if you look for them. On the other hand, turbo- or supercharged C5s and C6s in the 650- to 900-horsepower range have shown that strange things begin to happen at those levels. Axles break, lugs snap, sensors go funny...the list is long, varied, and usually hard on the checkbook.

In the end, of course, any debate over the relative excess of Z06 hotrodding is moot. Regardless of rationality, if there's more power to be found, somebody's going to find it. Doug Rippie sums the situation up perfectly: "The factory stability control won't be affected by extra power, but hey—I can't imagine that you can keep the tires under it even now."

 

[Rowdy1]

Very Good Article

The last words are the ones that seem to be the key...

"I can't imagine that you can keep the tires under it even now."

Then again, if "they" can make it run like that, "they" will figure out a way to make it hook up, somewhat:L

 

[korvettekarl]

Thanks 6 Shooter. Nice read and now I want to know EXACTLY where my name is on that long list of people waiting for thier chance at a new Z06.