Yay for a Ron Davis, boo for not getting the "Supercharger" version which is a little shorter. You know - for future use!
For a “halo” sportscar designed to be an off-the-shelf track-capable machine, the C5 Z06 sure has some substandard engine cooling capacity. It’s especially noticeable in autocross conditions, where full throttle runs are made immediately before parking the car with no airflow. Without airflow, the Corvette’s engine—which gets all its cooling air from under the nose while the car is in motion—heats up quickly and cools down slowly.
The smallish stock radiator is partly to blame for this situation. Honestly, it’s frightfully thin for use in anything resembling a performance car. Thankfully there are high-quality options that bolt right in like the unit we used from Ron Davis Radiators. Ron Davis has been building radiators for street cars, desert racing trucks, road race machines and custom applications for nearly half a century, and they have a drop-in option for the C5 that fits right in to the stock location and is nearly twice as thick as the factory rad.
Install is straightforward, if a little awkward. It’s a two-person job as it requires about 3.5 hands to hold various wire looms and hoses out of the way while the old radiator is lifted out and the new radiator is lowered in, but once the path is cleared it fits nicely into the original factory location. Its thickness requires a little Dremel work on the plastic upper support, but it’s worth the dust in your hair.
Our first experience with the new radiator post-install was a test day in steamy Moultrie, GA, where ambient temps were in the low 90s. We had actually done a test at the same site a couple months prior, in ambient temps about 5-degrees cooler, and were having to wait several additional minutes with the hood open, or take drives around the local roads after runs to get engine temps to stabilize properly between test runs. With the new radiator installed, off-course heat soak was greatly reduced, and engine temps would quickly stabilize back to the 200º-210º range shortly after a run.
Our new radiator also features built-in plumbing to run oil lines to and provide supplemental oil cooling. We haven’t taken advantage of that feature yet, but plan to as we add additional supplemental oil control to the car.
Yay for a Ron Davis, boo for not getting the "Supercharger" version which is a little shorter. You know - for future use!
Superchargers are lots of weight high and forward. making power with naturally-aspirated LS variants is too easy already. Under $7500 gets you a 495hp (before any bolt-ons) aluminum LS3 crate motor from GM with a warranty. Unless you're building a drag car a supercharger just seems kind of like overkill*.
(* which, of course, is the best kind of kill. But this is a car that will see most of its use on 200tw tires. There is a point of diminishing returns with power.)
Don't even bother with a crate motor. A cam swap and long tube headers can easily add 75rwhp.
I am making 410 whp and 395 ft-lbs of torque on a LS6 with forged rods and -2cc forged pistons, ceramic coated LG 1-3/4" LT headers, X-pipe with cats and a Comp 226/230 0.598/0.608 113+2 cam, a full Comp valve train upgrades with the stock 243 heads and stock LS6 intake, 78mm throttle body and descreened 85mm MAF. A FAST 90mm (older) or 92mm (current) intake with a LS2 sliver blade 90mm throttle body would add a few more to the total, especially with ported heads 
.
The Ron Davis (or DeWitts) fabricated full aluminum radiators are top notch, but are fairly expensive for those on a budget. The ECP units has been used by many with great results and its about half the cost. That fact that the C5 Z06 came from the factory without any oil cooler is almost criminal. Improved Racing offers a thermostatically control adapter block in three (3) temp ranges (depending on oil weight and usage) that should be used with any setup. Choosing the EOC in the radiator option can make things a bit easier with installation, but it is more of a "temperature equalizer" vs. using an external cooler. Also Improved Racing makes a trap door baffle kit for inside the later C5 2-pcs bat wing oil pan that is also highly recommended. Not sure if you have a catch can installed yet, but Elite Engineering offers a excellent kit.
As far as swapping in the GMPP LS3 crate engine into a C5 - there are a few of things that have to be done to convert to the Gen IV 58x control setup. Plus you are still dealing with factory powdered metal rods and cast piston, which may not be the best for use at the track. A rebuilt 6.0L/6.2L short block with a 24x crank, forged rods and pistons along with ARP fasteners would be a better option along with either the stock cathedral or later rectangle port heads/intake of your choice.
A few other LS6 coolant system pointers -
Make sure the foam is still in place around the shrouding. This helps to force all the high pressure air through the radiator and keeps it from spilling out the sides where it does no good..
Periodically clean out the radiator, a/c condenser and oil cooler (if installed) fins with compressed air and/or water spray from the back side.
When GM switched to the LS6 intake with its deeper plenum, due to clearance they removed the steam tubing/coolant crossover setup for the rear of the cylinder heads that was found on the LS1 engine. This can cause a problem in a LS6 that is being pushed hard at the track. A result has been that numerous LS6 engines have failed due to overheating issues with the back two cylinders. You can help prevent this by either - modifying the bottom of the LS6 intake manifold (remove the webbing) so there is clearance to install the LS1 tubing setup, install the front LS2 tube or the rear tube from a LS Vortec truck engine in the rear of the LS6 and tie either into the front hose leading to the radiator or you can install an aftermarket four corner tubing setup.
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