The history of the ZL1

Back in 1969, 69 Camaros were produced under a special code name called the ZL-1. At the heart of the ZL-1’s DNA were drag racing aspirations. Designed by a Dick Harrell and targeting the NHRA super stock class the Camaro was fitted with a 7.0 litre all aluminum engine pushing out 376 horsepower instead of the then standard 255hp V8.

69ZL1TRACO 01 Unveiling the 2012 Camaro ZL1Adding 47% more power to the package while stripping down weight through the use of an all aluminum engine block is exactly the recipe required for a higher power to weight ratio and great drag speeds. In road racing trim, the factory ZL-1s were able to clear the quarter mile in 12.1 seconds @ 116mph. Replacing the restrictive exhaust manifolds on the engine with tubular headers was rumored to bring power production closer to 550hp and running the car with aftermarket headers dumped after the collector with 9” slicks was proven to deliver a 10.9 second quarter mile @ a stunning 132mph for a car that was basically stock.

Recently, Chevrolet has announced the new ZL-1 line for 2012 and I was so impressed with the technical prowess of this car that I had to write about it. It seems that in the economic resurgence of the Detroit automotive companies Ford has gone heavily into the ‘app’ mentality with voice activated everything, rolling wireless hot-spots built into the car and high definition blue-tooth radio to allow you to stream your Pandora over the factory sound system.

It is refreshing to see Chevrolet’s take on modernization of their product lines with a deep injection of technology into the core product line. Reading off the specs of this new ZL-1 Camaro sounds like you’re reading off the technical feats of an Audi/VW, a brand which has long been known for it’s complex cars and their appeal to true car geeks. I don’t say that to belittle Chevrolet, contrary, my point is that Chevrolet has clearly set its eyes out on competing with the German Automotive companies which are considered to be at present the highest quality and highest tech manufacturers in the industry.

Here are the specs for the new 2012 Camaro ZL1:

At the heart of the package is the all aluminum 6.2 Litre LSA engine (originally prototyping for the ZL-1 started on the LS7 and LS9 but production finally settled on the LSA). Giving that this is a boosted application,  cast iron cylinder liners – measuring 4.06 inches (103.25 mm) in bore diameter are inserted into the aluminum block for increased strength. The bores are filled with Hypereutectic pistons (cast aluminum alloy pistons with a high concentration of silicone which gives them an increased strength through a unique crystal structure as well as a reduced expansion under extreme heat conditions allowing for tighter tolerances and higher combustion efficiency) of a 9:1 compression ratio. The pistons are cooled with oil squirters from beneath and the entire LSA oil system is beefed up with a larger sump oil pan and remote mounted oil cooler.

16 2012 chevrolet camaro zl1 1024x819 Unveiling the 2012 Camaro ZL1

The enngine is coupled with a 1.9 litre Eaton TVS (with its four twisted rotor design) positive displacement supercharger geared to 9 psi of boost. The supercharger blows through an integrated all black (for improved heat exchange) compact air to water intercooler core with a remote heat exchanger. Boost is then feed to a heat resistant A356T6 Aluminum alloy head fitted with 2 valves per cylinder. The head is fitted with a 2.16-inch (55 mm) intake valve and 1.59-inch (40.4 mm) exhaust valve. The valves are operated by hydraulic roller lifters actuated by what GM calls a ‘conservative’ camshaft with 12.2mm of peak lift and a very conservative overlap which is suited for a boosted application. The cylinder head is mated to the engine block via a 4-layer steel head gasket. And all the combustables exit the engine through a cast iron exhaust manifold feeding into a dual-mode exhaust system similar to that fitted to the current generation Corvette.

The result is 580hp @ 6100 rpms and a peak torque of 556 ft-lbs @ 4200 rpms.

Results:

ywlfbhlz 300x225 Unveiling the 2012 Camaro ZL1There are many other technical feats in this car including the Tremec TR-6060 six-speed transmission fitted with a 240-mm dual-mass flywheel matched with a 240-mm twin-disc clutch system for lightning fast shifts and delivering power to an upgraded rear end equipped with a factory limited slip differential for traction and safety.

The result of all of this technology is a car that “delivers more horsepower than a Ferrari 458, more torque than an Aston Martin DR9 V12 and a better power-to-weight ratio – 7.24 pounds per hp – than a Porsche 911 Carrera GTS.”

The car clears 60mph in just 3.7 seconds and is rumored to clear the quarter mile in under 12 seconds out of the box.

My comments on this engine:

1- Hydraulic Lifters:

First thing to note (and something many people might not realize) is that hydraulic lifters with fast bleed rates are an elegantly simple solution for achieving variable valve lift and variable duration out of a traditional grind camshaft. As engine RPM’s rise, oil pressure rises and as oil pressure rises the hydraulic lifter expands to its maximum extension delivering peak lift and peak duration at high rpms. At lower rpms though, with the lifter partially deflate, the engine can run up to 0.300” (7mm) less lift at idle as well as a reduced duration by as much as 10*. This makes it an ideal solution for getting a clean and stable idle out of a high lift camshaft fitted to a streetable engine. Furthermore, the low friction nature of roller lifters makes them ideal for camshaft profiles with steep ramps. Chevy claims that the 12.2mm of lift is conservative though that figure is typically not considered to be so, however it is very likely that the camshaft has a very steep ramp building up to peak lift and doesn’t spend a significant duration of time at that point making it more conservative in grind than it seems simply looking at the numbers

607d81f3 c20d 43fe 9558 a36b67a0005c Unveiling the 2012 Camaro ZL1

Illustration of 2 camshafts with the same peak lift with two different ramps.

2- Lift to Diameter ratios.

It’s commonly known that stock engines flow best with a valve lift to valve diameter ratio around 0.25:1 and with a ported cylinder head with higher peak flow velocities this ratio can be stretched out to 0.30:1 while still resulting in improved performance. After the 0.30:1 point most engines show diminishing returns with too big a flow curtain area where flow velocity at lower lift levels is compromised without any gain in peak flow.

With 12.2mm lift and a 55mm intake valve we find an LDR of 22% which is in fact somewhat conservative.
With a 12.2mm lift and a 40mm exhaust valve we find an LDR of 30.5% which is at the peak of what we expect for good desing.

3- Exhaust to Intake ratios

The ratio of diameter between exhaust valves and intake valves for a forced induction motor typically ranges in the 80% to 85% range for good design. Looking at a 40mm exhaust valve to a 55mm intake valve we find a ratio of 72% which is conservative for a forced induction motor and more typical for a naturally aspirated engine.

Seeing this explains the higher LDR of 30.5% on the exhaust side of the engine. The added lift on the exhaust side compensates for the slightly undersized exhaust valve, giving us a larger curtain area at peak lift and bringing peak exhaust flow back to reasonable numbers for an ideal intake to exhaust balance.

By doing so though, GM has gone conservative on the intake side of the engine with a conservative lift point which makes sense considering the intake charge is compressed due to the supercharger. The choice of exhaust lift has re-balanced this equation by compensating for the smaller naturally aspirated exhaust valve size.

4- Peak boost

Looking at our power calculator’s charger database, the Eaton R1900 is capable of a peak flow of 785hp and a peak boost of 21psi. Considering the LSA produces 580hp @ 9psi then we can expect to max out our supercharger at 785hp @ 17.5psi of boost.

5- Modifications

I think the following package of modifications makes sense on this engine:

  • Increase the supercharger gearing to max out at 17psi of boost
  • Increase the intake camshaft lift to maximize flow by reaching a 30% LDR giving us 16mm of lift (if possible depending on valve reliefs and clearance between the valve and the piston).
  • Once the boost is raised and the intake lift is increased, our exhaust side is definitely going to be overwhelmed, and with an already maxed out 30% LDR the only option here is to go to a wider duration camshaft with a narrower ramp (spending more duration at peak lift) to try and help evacuate more exhaust gas without oversizing the valve (which requires removal of the head) or increasing lift (which will reduce velocity at lower rpms).
  • With more boost and heat flowing through the system, the stock air to water intercooler should be able to handle the added cooling demands so long as it always has a fresh supply of cool water. This potentially means a larger reservoir and a larger heat exchanger but the intercooler itself need not be upgraded (similar cooling upgrade kits are typical on cars like the E55 AMG and support in excess of a 40% boost in power using the stock core).
  • Look into the cast iron exhaust manifolds and potentially replacing them with tubular units resonance tuned for peak at 6100 rpms. With the supercharger now geared for 17psi of boost, we should not face any problems with sacrificing low end torque for high end power with redline tuned headers.
  • Remap the ECU for 35% more fuel flow at peak and potentially around 5 degrees of extra timing retard at peak boost at redline.
  • On the Corvette Dual Mode exhaust the 3” pipes neck down to 2.5” near the muffler inlets. Swapping the axle-back section of the exhaust to a true 3” section (while retaining the stock control valve for quiet idle and cruise) is worth about a 10hp increase at the ~450hp level. Considering we’re planning on pushing power out to 785hp, the power deficit of the dual 2.5” exhaust vs a true dual 3” will be even more.
httpv://www.youtube.com/watch?v=rqYzRRJtcGw&feature=player_embedded
Considering all of the modifications here are ‘bolt on’ modifications that can be performed over a series of consecutive weekends without having to tear down the engine or swap superchargers, then I’m pretty sure that we’re going to see some really SICK ZL1’s hitting the drag strip over the next few years and that to me is really exciting.Read more: