Skip to main content


Showing posts with the label Tuning

C6 tunnel plate upgrade

The tunnel plate was initially designed as a heat barrier between the exhaust and the torque tube, but the GM engineers discovered that a thicker plate reduced the torsional flex in the chassis, which was then used in the C5R race cars. With the tunnel plate already removed for servicing the drivetrain, this was a nice opportunity to upgrade the tunnel plate in my C5Z. The Elite Engineering and TPS Motorsport tunnel plates became all too expensive when adding overseas shipment, so I sourced a used C6 tunnel plate. Except for the increased thickness, the C5 and C6 plates are geometrically indentical, so upgrading to the C6 tunnel plate is plug & play. The C5 tunnel plate is an 1.6 mm sheet metal plate.With the introduction of the C6, the tunnel plate thickness was increased from 1.6 to 3.2 mm. The torsional rigidity of  aluminum increases with increasing thickness. This is because thicker materials have a larger cross-sectional area, which results in a greater resistance to torsion.

Monitoring critical engine data

  The stock head unit is removed and replaced with a small single board amplifier. I used the free space to mount a 8 inch tablet running Microsoft Windows. By using a HP Tuners OBDII-adapter and the VCM Scanner application, I can monitor engine data which is critical during track days. The gauges turn red when any values are below/above defined thresholds, e.g. oil temperature above 130°C (266°F) or oil pressure below 20 psi, so only a quick glance can give an overview of the status.

Transmission fluid temperature in the DIC

Did you know that the Z06 has a differential fluid temperature sensor that allows you to read the temperature in the DIC*/LCD display)? The reading is not available by default, but is added to the DIC after a "high trans temp" warning, which is activated when the transmission temperature exceeds 130°C (266°F) for more than 10 minutes. The trans fluid value can then be selected for viewing in the DIC similar to oil and coolant temperature. The sensor is a part of the the fluid fill plug in the T56 transmission.  The high thresholds are also why most owners have never seen the warning, as it will hardly ever happen during normal use. During continous heavy load on track days or circuit racing, the warning thresholds are actually too high. The fluid temperature can raise far beyond 130°C before the driver is notified, due to the 10 minute delay. Above 130°C, gear oils starts to break down and lose its viscosity. This can create a viscious circle of increasing friction and temper

Spec Stage 2 clutch kit with aluminium flywheel

Lightweight aluminium flywheel with steel insert Worn slave cylinder At 110k miles (178 000 km), the car had developed the "clutch pedal stuck to floor"  issue when shifting at high RPMs. This is caused by a worn slave cylinder, where worn seals allows dust to enter the circuit and cause the slave cylinder to get stuck by the high inertial forces and the increased friction. A sure sign of this happening is that the clutch fluid gets discolored again quickly after a change. State of stock clutch The car still had the stock clutch, which was in a surprisingly good state for the milage. Minimal surface wear and only a few small hotspots, one could even mistake the clutch disk for a new item.  So the OEM clutch from LUK is more than capable of handling the LS6 stock power.  However, with everything else disassembled, it would be dumb not to replace the clutch now, as it will probably not last another 20 years. Spec Stage 2 clutch kit I had originally purchased a LUK OEM clutch ki

Built 4.10 rear differerential

Late April, and the spring finally arrived with temperatures making it possible to start on the pending repairs.  I started by draining the oil from the noisy rear differential. This is what the T-1000 Terminator is made of; liquid metal drained from a Getrag differential. A magnet picked up a lot of metal shavings.  The output shafts have significant play, which is an indication of worn clutch packs and belleville washers, and possibly broken output shaft stubs (I will find out when I disassemble the differential later). With all these issues, this differential needs a complete rebuild. It is hard to find specialists with the knowledge and the tools required to perform this work in Norway. The cost of shipping the differential to the USA and back for a rebuild is also excessive, due to the weight. So, the conclusion was to purchase a built 4.10 differential, which obviosly also gave the opportunity to change to a different gear ratio. Built 4.10 differential C6 Z06 output stub shafts

Larger 330 mm rear brakes from C6 Z51

Don't drive with your nannies on! With active handling in competitive driving mode, yaw control is still active and using the rear brakes to correct excessive yaw on corner entry/exit. This is not an issue on regular street driving, but on a racing circuit this continuous correction causes the rear brakes to overheat. In my case one of the rotors cracked as the car cooled down in the pit. I even heard the *PING* as it happened. 305 to 330 mm brake rotor After some research, I found that the C6 with the Z51 option code uses a larger 330 mm brake rotor, but still share the same caliper and parking brake dimensions! Plus Increased thermal capacity. The EBC Z51 rotors are ventilated on both sides, have a higher mass and increase the swept diameter of the brake pad Better looks, the brakes fill the 18" wheel and looks more in balance with the front big brake kit. Reuse of stock brake calipers and parking brakes Minus Change of brake brake bias. The increased rotor diameter causes a

Trackspec T1 hood vent

Heat management is still an issue on track days, so I decided to add a Trackspec hood vent. Trackspec T1 hood vent Optimized louver design to maximize extraction flow velocities within a vehicle in motion Reduces under hood pressure delta to reduce front end lift and increase net vehicle downforce. Significantly reduces under hood temperatures by extracting heat and allowing fresh cold air to enter the engine bay. Maximize life of engine accessories by reducing overall operating temperature. Increases dense, cold air flow through radiator to promote lower coolant temperatures. -exactly what my C5Z needs! I managed to source a second hand T1 hood vent in good condition. For the install, I decided to use countersunk hex screws rather than pop rivets, as I don't like the look of pop rivets (it is not a kit car, after all). To countersunk a screw, you need enough material thickness for the screw head. I looked up some tables and concluded that M3 (3 mm) screws would work. An Ø6.3 mm 90

Upgrade from 16 row to 30 row oil cooler

Engine oil temperature, the never ending story part #3 The 16 row oil cooler did help to lower the oil temperature, but not enough. I was advised that the absolute minimum was 25 rows, so I sourced a new 30 row oil cooler. I have to admit that I'm using a "Made in China" product, but the cost of a Setrab or Mocal was too high at this time. The G-PLUS brand does feature a stacked setup, but it might be that a Setrab or Mocal have a higher cooling capacity (BTU). I'll now when I get rich and buy a Setrab... 90 degree AN-fittings can cause flow restrictions, so I chose to bend the hoses when mounting the 16 row cooler. With the larger oil cooler, this was no longer possible as the bends would get too tight. To my luck, AN10 90 deg fittings still have a large cross section so the engine oil pressure didn't drop.

4 wheel alignment for circuit racing

It was time for a wheel alignment after installing poly suspension bushings. I also wanted to a more aggressive geometry better suited to circuit racing. I asked for zero toe front and rear, which in my experience evens out the wear caused by the negative camber. I also like the handling with zero toe.

Auto-Blip, down-shift rev-matching

My CPU appears to have limited processing power, spending too much time to complete a successful rev-matched down-shift while braking at the same time. The end result is that I brake too much and too late, burning off too much speed. As my CPU is a one-off special edition that can't be easily upgraded, I decided to help it with a co-processor - the Auto-Blip Intelligent downshifter. After a quick test drive after installation, I conclude that two brains works better than one. I can now focus on driving the car, while the Auto-blip handles the rev-matching. The ever so difficult downshift to 2. gear is now a breeze. Designed to fit in that spot? The Auto-Blip kicks into action when you brake and clutch simultaneously, blipping the throttle at a configurable delay. The amount of throttle blip (how much the revs increase) is also configurable. I did have some issues getting the unit to work in my C5Z. The manual states to only connect two off the APP sensors (throttle position sensors

Hoosier A6 tires on square setup, 18x10.5"

I managed to source a set of C5 Z06 18x10.5" replica wheels with 315/35-R18 Hoosier A6 tires. It will be interesting to see how the A6s perform on circuit racing, as they are designed for short autocross sessions generating less heat. Sticky tires like these will not work with the stock suspension rubber bushings. Even if you adjust maximum negative camber, the rubber will deflect too much under load and screw up the alignment. End result is that the sticky tires can wear out in short time, especially the outer shoulder. To give the tires a chance to survive I'm installing poly bushings and changing to  more aggressive suspension geometry  settings.

Square setup with 4xC5Z OEM rear rims (18x10.5")

With the original staggered setup, the wheels can't be rotated to even out tire wear. This is a big minus as the front and rear tires wear quite differently. This can be solved by using the same rim and tire dimensions front and rear - a square setup. The wider front tires also improves the front end grip and shift the chassis balance rearward, which I prefer. The 14" Wilwood Aero 6 brake kit requires 18" inch wheels, and are known to fit behind the C5Z rear rims. I was fortunate to get two OEM rear Speedline C5Z rims from House of Wheels at a good price, in the same finish as on my car (there are variations in color).  They even survived the long distance travel from the USA to Norway without any dents. I have to issues with this configuration, no wheel arch or liner rubbing. This is how GM should have configured the C5Z.

Wilwood Aero 6, 14" big brake kit

The stock brakes hold up surprisingly well on track days, but rotors and brake pads burn off at an alarming rate. 2 track days on the rotors, 1-2 track days on the brake pads. I put a request on to purchase a second hand big brake kit. I got hold of an Wilwood Aero 6 kit, complete with spare parts and an additional set of new rotors.

Energy Suspension poly bushings install

Based on experience with tyre wear from the previous season, I knew that a set of Hoosier A6s wouldn't last long with the stock setup. With sticky tires, the rubber bushings deform too much, throwing off the alignment. Time for an upgrade. I was lucky to source a front and rear Energy Suspension poly bushing kit that someone had purchased, but not installed. Removing and reinstalling the upper and lower suspension arms was easy, although quite a bit of work on the rear, as the driveshafts have to be removed. The real challenge was to remove the rubber bushings. I tried with basic hand tools and a bench vise, but quickly gave up on the first bushing. Time to expand the toolset in the garage. A hydraulic bench press would be nice, but would take too much time - and money - to source. I found a nice toolkit for removing and installing bushing in the local hardware shop, which made the work surprisingly easy. With this toolset, you only need hand power to remove the bushings. The tools

Engineering Cooling Products (ECP) radiator

With a large oil cooler in front of the radiator, I noticed that the water temperature exceeded 115 °C. At such temperatures, the ECU starts to pull timing to reduce engine power output. I resealed the radiator shroud, cleaned out debris, installed a 160  thermostat (71 °C) and lowered the fan settings with HP tuners, but this was still an issue. The stock radiator had developed a hairline crack in the plastic end tank, which I discovered by luck when running the engine without the radiator and the fan shroud removed. A DeWitts or Ron Davis radiator was my preferred solution, but after adding shipment costs and import taxes the total was above $1000, so I decided to go for the less expensive Engineering Cooling Products (ECP) radiator for the C5. The ECP radiator arrived without any visible damage, which is always a risk when having fragile parts transported long distance. I bought it with a consumable electrode, to replace the flimsy petcock supplied.  The radiator installed nicely an

Flipped airbox to lower air intake air temperature

While stationary in the pit lane on a track day, I observed the intake air (IAT) temperature exceed 70°C. It took almost a full lap at speed to cool down the intake air again. High intake temperature sets of a series of events which reduces engine power and response. Increased risk of engine ignition knock / detonation The engine ECU retards ignition timing above 30°C IAT If the ECU detects ignition knock, the ignition timing will be further retarded by the ECU Time to do some improvements! By cutting the radiator shroud and inverting the airbox, colder air is drawn from the outside the engine bay. The most noticeable improvement afterwards is the IAT drops quickly after leaving the pit lane on track days, which was my main goal.

Adding a 16 row engine oil cooler

During the previous track day at  Vålerbanen in July 2020 , I had to run the engine at maximum of  5500-6000 rpm to keep the oil temperature below 140 °C if the session lasted more than 10 minutes. The C5 Z06 does not come from the factory with an oil cooler, but it is clearly required to avoid overheating the engine.  The stock temperature sensor is M12x1.5 while the oil cooler block is 1/8 NPT. I decided to drill and tap the correct M12x1.5 thread, which worked out nicely. I thoroughly cleaned out debris using brake cleaner and compressed air.  Oil cooler brackets being made Finished brackets New oil cooler block installed. The part of the hoses passing by the exhaust manifold are protected by additional heat insulation. This block  has no thermostat, as I simply cover the oil cooler with a sheet metal plate when not doing track days. A thermostat also restricts the oil flow, by the nature of its design. Oil cooler installed. I decided it had to be installed in front of the radiators