You haven't seen our 2006 Corvette project car since summer 2007, and we admit, that's a long time. (More than enough time, even, for some readers to have gone from bachelorhood bliss to diaper duty.) We have no excuse, really; but we will say we've had a more-than-sufficient opportunity to mull over just how to crown this story series.
Our express purpose from day one has been to try and duplicate Z06 performance for a fraction of the price. In this, our final installment, we'll perform our last set of mods and hit the dyno to see just how close we got. But before getting into all that, we do have one piece of unfinished business to mention, and that is regarding the aftermarket clutch we installed back in our penultimate segment ("Preemptive Strike," August 2007). As it turns out, our SPEC Super Twin exhibited excellent streetability. We found nothing but smooth engagement during the great majority of starts, and even when it did show up once in a while, clutch chatter was quite livable, especially for a clutch with a 900 lb-ft capacity. We should point out that, again, we installed SPEC's entry-level Super Twin, which features its least-aggressive friction compound; we'd imagine SPEC's higher-horsepower materials would probably be a little grabbier. We also noticed the shifter glides through the gears with less effort, reportedly a result of more complete clutch disengagement. One aspect of this clutch system that took a little getting used to is that the pedal grabs a bit higher than stock and has a somewhat shorter range of engagement-but SPEC says this is fully intentional, to enable quicker shifts. Probably the only real downside to this clutch system-and one that has nothing to do with performance or driveability-is that there is some additional gear rattle in neutral with the clutch out, which according to SPEC is a result of having two disc plates, each with a higher clutch disc damper spring rate.
'Nuff said on that, so back to the case at hand. We've stated all along that we were planning on keeping this project naturally aspirated, and are sticking to that promise. With our C6's LS2 bone-stock from the coil packs down, this made the next obvious choice from a power perspective a head/cam package. But we decided to do things a little differently so as to both maintain stock-like driveability and to keep options open for forced induction further down the road. Therefore, we're opting to leave the stock cam in place and forgo having to put in a bumpstick that would be a compromise between N/A and boosted power. So although ponies will be left on the table with a head-only swap, it leaves the project more open-ended for the purpose of future upgrades, among other things (e.g., idle quality, less attention from the boys and girls in blue, et cetera).
Trick Flow Specialties, a proven name in LS performance, supplied us with a set of its GenX Street/Strip CNC-Ported Cylinder Heads. While there's a handful of cylinder head types TFS offers for LS engines, we're using the LS2 version of the head, which has 225cc intake ports, 65cc combustion chambers, and 2.055-inch intake/1.575-inch exhaust valves. (LS1 versions, for example, feature a 215cc intake port along with slightly smaller combustion chambers and intake valves.) There's a ton of technology in these TFS heads: they feature 5-axis fadal machined combustion chambers, and intake and exhaust ports with minimal machining stepover for max flow. The valve jobs are done using high quality Serdi machining centers for high concentricity from the valve to the valve seat, less runout, and a longer lasting valve job.
High-quality Ferrea stainless steel valves, ductile iron valve seats, high quality double valvesprings good for up to 0.600 lift, bronze alloy valve guides, and Viton seals round out the package.
Our complete "head package" for the project. The main items, of course, are Trick Flow's GenX Street/Strip CNC-Ported Cylinder Heads in 225cc form, fully assembled with valvesprings good to 0.600-inch lift (PN TFS-3060T001-C02, $2,395). Also shown is our set of TFS chrome-moly pushrods (PN TFS-21407500, $86), as well as Harland Sharp roller rockers (PN CSP-SLS17, $399), ARP Pro Series head bolts (PN ARP-134-3610, $111), and GM MLS head gaskets (2 x PN NAL-12589227, $90 for the pair).---->
In its current form, our LS2 puts 376.8 hp to the tires, benefiting solely from an aftermarket air intake and throttle-body spacer, headers, and a cat-back. And while its LS2/LS6 heads aren't a bad factory piece, they've seen their last days under this Vette's hood.---->
First order of business: disconnect the battery ground, then take off the engine covers and remove the induction system forward of the throttle body (in our case, this consists of a VaraRam ram air kit-see "Ethereal Rush," March 2007). The throttle body can stay on the intake.---->
Summit Racing Equipment provided us with everything needed for the install, including rocker arms, head gaskets, pushrods, and head bolts; see the photo captions for more information.
Note that Trick Flow also sells its heads and other necessary components paired with a camshaft as full "Top-End Engine Kits," and several versions are available for select LS engines that make between 485 and 515 rwhp. Indeed, the company tells us that adding a cam to our current recipe would pick up 30-40 more horses, and there is no question that this is the way to go if you're looking to optimize N/A performance. A higher-lift, longer-duration cam (the stock LS2 unit specs out at 204/211 duration at 0.050, 0.525/0.525 lift, 116 LSA) would definitely take full advantage of the added flow capabilities of the TFS heads.
But that's not our plan for now, so with that background information out of the way, let's get going on the install.
It's time to pass judgment on just how well we did accomplishing our initially stated tasks. The final bill for the mods we've undertaken breaks down as follows (pricing current as of their respective dates of publication):
Note that the Innovate O2 is not a necessary part of the build, and in the case of the B&M shifter, it offers a distinct advantage over a stock Z06 unit, so these should probably be kept out of consideration for an apples-to-apples comparison (ditto for the SPEC clutch and DTE diff strut). This cuts $2,234 from our grand total, leaving us with $7,237 worth of mods to compare to a Z-car. That money spent pales in comparison to the extra $25 large you'd need to pony up for a new Z06. Even still, a no-excuses grand total of $56,006 for the vehicle you see here (including the $46,535 vehicle sticker price, but not including tuning, sales tax, or shipping) is almost exactly what you'd pay for a brand-new C6 convertible. The price disparity when shopping for used C6s vs. C6 Z06s would of course not be as much, but it's still significant. And of course, the Z06's advantages in handling are not being taken into consideration, since most readers "live their lives a quarter mile at a time" (bad joke, for those of you misfortunate enough to have sat through a certain Hollywood atrocity that shall remain nameless).
So while we did not achieve our stated goals of meeting or exceeding the 445 or so rwhp of a stock Z06, you can chalk most of the remaining difference up to false knock. Indeed, we don't consider this project a failure in the least: even a mild-to-moderate cam swap would easily put this car at Z06 power for just a few hundred bucks (and a supercharger, way beyond), but again, we didn't want to be doubling the work and re-swapping should a blower be chosen down the road.
We speak of possible mods to come, yet also of the completion of this project in the pages of GMHTP. Why? Because we've pretty much decided there needs to be a little room in the garage for a 2010 Camaro SS. So while the Vette's stay in the Werner household is likely limited, we've created what we think to be a great ride that's a no-excuses daily driver, and looks and sounds stupendous-simply put, it has made Chevrolet's fantastic sixth-gen Corvette even better, and that's no small feat. Regardless of whether he or she adds any further modifications, we hope the next owner will enjoy this gorgeous C6 as much as we have!
The fuel feed line is disconnected from the rails (which can also stay on the intake) via a 3/8 disconnect tool. Also at this point (not shown): the coil brackets come off. Disconnect only the large white plugs (seen just below my left hand here), then the five stud-headed bolts holding each coil bracket to the valve cover (you may have to loosen the upper alternator bolt a bit to get a socket on the forwardmost bolt on the driver side). You risk less damage to the plug wires if you disconnect them from the spark plugs and not the coils.---->
To get the alternator out, first disconnect its electrical connections, including the black plug and the fat red wire (the latter via a 13mm). Peel this wire's harness off of the top of the engine (it's routed under the fuel rails), and clump it out of the way over by the brake booster. Then the two 15mm alternator bolts come out, and after a sideways pry, the alternator is free from its bracket. Now also isn't a bad time to disconnect the coolant temp sensor in the front of the cylinder head, as well as all four driver-side injectors, and tuck this whole electrical harness out of the way (do the same for the similar harness on the passenger side).---->
At this point, we opt to take the hood off-not only for photography purposes, but for improved access at the front of the engine (though it's by no means mandatory). Time to tend to the headers; while underneath loosening the collectors where they meet the X-pipe, we also drain the engine coolant. Lo and behold, this car actually has a petcock!---->
A bit of clarification to Harland Sharp's installation instructions is in order. First, lifter preload must be checked. With both valves closed on cylinder 1 (remember we've left the crank at this cylinder's firing position), the rocker pair is installed and the bolts tightened just until each pushrod can no longer be jiggled or turned, representing zero lash. From this point, each bolt should turn within the range of 3/4 and 1 1/2 turns before reaching the final tightening torque of 22 ft-lb. We find that the intake takes 1 turn and the exhaust 1 1/4 turns, so we're OK and don't need different length pushrods. The rockers are then removed, their pushrod cups lubricated, and they're reinstalled. With cylinder 1 taken care of, we proceed along the firing order of the engine (1-8-7-2-6-5-4-3) 1/4 crank turn at a time, installing each rocker pair as we go. Also, Trick Flow's instructions state to use Teflon tape on the intake bolts, but we use threadlocker instead (this stuff usually seals well too). Here we install the rockers on cylinder 2.---->