Guys (& ladies), first you can’t compare the S85 engine with any other BMW engine, including the E39 M5 or any of the Porsche engines, many of which were designed for forced induction from the beginning.
While there may be aftermarket blown Z06s on the street, none of them are official Chevy products. As I said before,
bolting on a blower is easy, modifying an engine not designed for forced induction to last is not.
The ZR1 and M5's engines were designed to produce power through opposite methods.
Supercharging an engine produces increased power, (heat and stress) at low RPM. At high RPM the blower's parasitic power drain is significant. According to Jaguar, their supercharged engine consumes 100 h.p. at max rpm. BMW designed the S85 to produce power at high rpm by using low-mass engine reciprocating components (light weight valves and hollow camshafts) and avoiding extreme torque, instead allowing the driver to extract super performance by "revving" the engine. The engine also uses an ion analysis knock sensor system, that might not work properly with different density fuel charges. (More below)
Following are outlines of each engine. Read for yourself and decide whether supercharging is a smart choice for you. It's your car and money.
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Corvette ZR1/LS3 engine
"The engine is based on a modified LS3 6.2-liter block (
the LS7's cylinder walls are too thin to withstand boost), with the addition of oil squirters. These squirters direct cooling oil at the underside of the pistons, and are critical to helping the LS9 handle the increased temperatures that come with supercharging.
The LS9 is assembled by hand at GM's Performance Build Center, a unique, small-volume engine production facility in Wixom, Mich., that also builds the Corvette Z06's LS7 engine and other high-performance GM production engines.
Cylinder Block and Reciprocating Assembly Details
The LS9's aluminum cylinder block features steel, six-bolt main bearing caps, with enlarged vent windows in the second and third bulkheads for enhanced bay to bay breathing.
Cast iron cylinder liners - measuring 4.06 inches (103.25 mm) in bore diameter -
are inserted in the aluminum block and they are finish-bored and honed with a deck plate installed. The deck plate simulates the pressure and minute dimensional variances applied to the block when the cylinder heads are installed, ensuring a higher degree of accuracy that promotes maximum cylinder head sealing, piston ring fit and overall engine performance.
2009 Corvette ZR1 LS9 Engine Crankshaft
Nestled inside the cylinder block is a
forged steel crankshaft that delivers the LS9's 3.62-inch (92 mm) stroke. It features a smaller-diameter ignition-triggering reluctor wheel and a
nine-bolt flange - the outer face of the crankshaft on which the flywheel is mounted -
that provides more clamping strength.
Other non-supercharged 6.2L engines, such as the base Corvette's LS3, have a six-bolt flange.
A torsional damper mounted to the front of the crankshaft features a keyway and friction washer,
which also is designed to support the engine's high loads.
Attached to the crankshaft is
a set of titanium connecting rods and
forged aluminum pistons, which, when combined with the cylinder heads, delivers a
9.1:1 compression ratio. This combination is extremely durable and lightweight, enabling the LS9's high-rpm capability.
Cylinder Head Details
The basic cylinder head design of the LS9 is similar to the L92-type head found on the LS3 V-8, but
it is cast with a premium A356T6 alloy that is better at handling the heat generated by the supercharged engine - particularly in the bridge area of the cylinder head, between the intake and exhaust valves.
In addition to the special aluminum alloy, each head is created with a rotocast method. Also known as spin casting, the process involves pouring the molten alloy into a rotating mold.
This makes for more even distribution of the material and virtually eliminates porosity - air bubbles or pockets trapped in the casting - for a stronger finished product.
Although the heads are based on the L92 design, they feature swirl-inducing wings that are cast into the intake ports. This improves the mixture motion of the pressurized air/fuel charge. The charge enters the combustion chambers via titanium intake valves that measure 2.16 inches (55 mm) in diameter. Spent gases exit the chambers through 1.59-inch (40.4 mm) hollow stem sodium-filled exhaust valves. The titanium intake and sodium-filled exhaust valves are used for their lightweight and high-rpm capability.
To ensure sealing of the pressurized engine, unique, four-layer steel head gaskets are used with the LS9's heads.
Supercharger and Charge Cooler Details
The LS9's R2300 supercharger is a sixth-generation design from Eaton, with a case that is specific to the Corvette application. The supercharger features a new four-lobe rotor design that promotes quieter and more efficient performance, while its large, 2.3-liter displacement ensures adequate air volume at high rpm to support the engine's high-horsepower aspiration.
Maximum boost pressure is 10.5 psi (0.72 bar).
The supercharger is an engine-driven air pump that contains a pair of long rotors that are twisted somewhat like pretzel sticks. As they spin around each other, incoming air is squeezed between the rotors and pushed under pressure into the engine - forcing more air into the engine than it could draw under "natural" aspiration. The rotors are driven by a pulley and belt that are connected to the engine's accessory drive system.
2009 Corvette ZR1 LS9 Engine Intercooler
Because the pressurized air is hotter than naturally aspirated air, the LS9 employs a liquid-to-air charge cooling system to reduce inlet air temperature after it exits the supercharger - reducing the inlet air temperature by up to 60 degrees C (140 F). Cooler air is denser and allows the engine to make the most of its high-pressure air charge.
The charge cooling system includes a dedicated coolant circuit with a remote-mounted pump and reservoir.
The design of the supercharger case and its integrated charge cooling system was driven by the space and dimensions afforded under the Corvette's hood. To that end, the charge cooler was designed as a "dual brick" system, with a pair of low-profile heat exchangers mounted longitudinally on either side of the supercharger. Coupled with the supercharger itself, this integrated design mounts to the engine in place of a conventional intake manifold and is only slightly taller than a non-supercharged 6.2L engine. The air inlet and rotor drive pulley are positioned at the front of the supercharger.
Water pump:
To compensate for the heavier load generated by the supercharger drive system, an LS9-specific water pump with increased bearing capacity is used.
Accessory drive system: In order to package the accessory drive system in the Corvette's engine compartment, the supercharger drive was integrated into the main drive system. This required a wider 11-rib accessory drive system to be used with the LS9 to support the load delivered by the supercharger.
New Six-Speed Manual Transmission
The Corvette ZR1's LS9 engine is backed by a Tremec TR6060 six-speed manual transmission, with a twin-disc clutch system. It is based on the proven T56 six-speed, but
upgraded to handle the LS9's torque output and delivers improved shift quality."
LS9 Engine Details - Supercharged 2009 Corvette ZR1 Powerplant - Vette Magazine
2009 Corvette ZR1
Chevrolet Corvette Zr1 Ls9 Engine Specifications Ls9 Camshaft Photo
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BMW S85 engine
"The V10 is designed around BMW's high revving concept.
Instead of setting high torque as the goal and achieving that through supercharging, BMW engineers sought superior driving performance through high revs and a surplus of power at the rear wheels much like a racecar. The S85 borders on racing engine technology with its
12.0:1 compression ratio, unique engine management and continued power output at unconventionally high engine speeds.
Its redline is 8250 rpm; its
maximum power of 500 hp is achieved at
7750 rpm and its
maximum torque of
383 lb-ft. is realized at 6100 rpm.
This strategy, which avoids extreme torque and instead allows the driver to extract super performance by "revving" the engine, facilitates the use of relatively light, low-mass reciprocating components inside the engine.
Structurally
the S85 is the first BMW V engine to use a bedplate design. The bedplate is
an aluminum structure with cast iron bearing inserts that replaces individual main caps to help distribute from the crank across the entire block. BMW even went to design unique self-centering main bolts that assure better stress distribution and obtain uniform bolt deformation.
The M5 V-10 does not employ the Valvetronic system now found in BMW's regular-production V-8 and V-12 engines as well as the N52 and the turbocharged N54 6-cylinder powerplants. Though Valvetronic eliminates the energy-wasting action of throttles, it is not (yet) suitable for high-rpm engines. Instead, the M5 V-10 uses a typical BMW M valvetrain with 4 valves per cylinder actuated by "box-type" hydraulic lifters developed for motorsports. These are small, lightweight and extremely rigid, as they must be to survive an 8250-rpm environment. They are also specially shaped for efficient valve operation, with an oblong cross-section (not round like bucket tappets), slightly curved contact surface and guiding tab to ensure a consistent position in their bores.
The
valves themselves are also light, with stems of only 5 mm/0.2 in. And, as on the new six-cylinder engines,
the camshafts are hollow, further reducing inertia and enhancing engine response. Altogether, the valvetrain's reciprocating mass has been reduced 17.5% from the previous M5's engine; an important facet of the high-rpm concept. So are the light, but ultra-strong pistons and connecting rods.
The higher redline of the engine is also requires less valve-train mass, which for the S85 was reduced by 17.5%. Operating this is a new generation bi-VANOS system that uses higher hydraulic pressure, 80 bar (1160 psi) for faster actuation of the sliding gearbox that phase the camshafts.
M engineers and Bosch developed the MS S65 control unit specifically for the M5. Equipped with three 32-bit processors, this unit capable of performing 200 million individual calculations per second. The MS S65 reads 14 digital and 44 analog signal inputs and outputs to 62 channels and 10 serial ports, which is comparable to the system used on their F1 engine. This is eight times the processing power of the E46 ECU of only four years ago.
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BMW makes its first introduction of a combustion charge ion analysis system first to be implemented on the S85. Similar to Saab's system of the 90's and based on theories developed in the 30's,
this ion analysis takes the place of a conventional knock sensor by monitoring the combustion event and combustion pressures for each cylinder. Using the spark plug as a positive pole and the cylinder as a ground, the ion current system measures the conductance of the air fuel charge throughout the combustion process. As combustion takes place and the charge chemistry changes, so does the electrical conductance of the contents of the cylinder. Based on the conductance as a function of crank angle, each individual combustion event is evaluated to better refine and control the sequential fuel and spark maps on a per cylinder basis. This is basically like a very smart version of an automotive oscilloscope. Unlike previous attempts of combustion ion charge analysis, the BMW system also discerns misfires either from inadequate fuel or spark, something neither Saab's system or a knock sensor can do."
BMW E60 M5 - European Car Magazine
2007 BMW M5 6-Speed Car Review and Specs | 2007 BMW M5 6-Speed Car Wallpaper Pictures Pics
The E60's clutch assembly is a weak link in the power train. Although manufactured of a heavier design, it's no larger than the unit used in the E39 M5. My S.A. told me it's not designed for city driving and the assembly on my beast has been rebuilt twice in the first 16K miles. I've typically gotten 50K - 80K before first clutch rebuilds with previous manual transmissions.
The E60's rear differential is also a weak link, the reason BMW initially disabled DSC Off with 6-speed models.
With aftermarket heavy duty parts, our beast's could be bulked up to handle the extra power, although IMHO turbocharging would be preferred and the cost high. Still don't know whether the ion analysis system would work properly and someone besides Steve Dinan would have to crack BMW's software encryption.
Finally, compared to the Corvette, how many heavy duty aftermarket parts have you seen for the E60 M5?
