c4c5specialist
Technical Advisor
HI there,
These LS7 classification has been under validation for a while now. The following are fact, as far as changes for the new design.
First, the reasoning for the changes are as follows.
Adding a second intake valve improves intake air flow, which provides some value, but perhaps more importantly the design relocates the exhaust valve and the spark plug within the combustion chamber. The exhaust valve moves from alongside the intake valve to the other side of the cylinder, so less exhaust heat transfers to the intake port. The resulting cooler intake charge boosts power and efficiency.
Positioning intake and exhaust valves on opposite sides of the combustion chamber leaves space in the center for the spark plug, which improves combustion efficiency. Together, these improvements boost power output by 10-15%.
The three-valve engine has the intake valves in a straight line, operating them with a forked rocker arm off a conventional rocker shaft. The solution is a pair of rocker arms. One mounts on the rocker shaft where the exhaust rocker arm would be on a two-valve engine. Instead of acting on the valve, however, the first rocker pushes on a short, nearly horizontal pushrod that runs across the head to a freestanding stud-mounted rocker arm. A short, nearly horizontal pushrod links the intermediate rocker arm located on the conventional rocker shaft to the stud-mounted rocker that opens the exhaust valve. A forked rocker arm operates both intake valves. This second rocker arm pivots the movement into the right direction for the exhaust valve.
The three-valve heads are about 1 in (25 mm) wider than the two-valve heads, but they maintain the low profile that is an advantage of OHV engines. The new heads will work with the displacement-on-demand (DOD) cylinder-deactivation system that will arrive on the two-valve Generation IV engine.
"The three-valve design adds complexity but uses the type of components with which GM is very familiar, so reliability shouldn't be a problem," said Frederick Rozario, Development Engineer, Advanced Powertrain at GM. "And while the added mass in the valvetrain might seem to be an obstacle to high rpm operation, the Corvette engine will rev to 7000 rpm with a 30% margin of safety. It can go to 8000 rpm safely," he added. A special jig will hold the parts together so the whole valve actuation assembly can be installed as a unit on the head. "A weakness of single camshaft engines is the inability to separate intake-cam timing from exhaust-cam timing for maximum efficiency and minimal emissions. But a cam phaser that adjusts the advance or retard of even a single cam, depending on conditions, is still very valuable,"
"The cam phaser on this engine provides 80% of the benefit of a system with separate intake and exhaust phasers." The phaser mounts under the water pump in the traditional timing chain location, so it does not require any additional space underhood. The water pump is new too, because the higher-output engine increases the demand for cooling. The 6.3-L version of the engine will produce 500 hp(373 kW), for example. So the new pump produces twice the 80 gal/min (300 L/min) of coolant provided by the two-valve engine's water pump. The V8's is a two-phase oil pump, switching between high and low flow as needed to maintain the necessary oil pressure without suffering excessive parasitic losses when lower pressure is sufficient The engines also feature optimized exhaust manifolds with equal flow runners for each cylinder.
The exchange factor between c5 and c6 has been theorized alot. Fact is that the oiling system of these engines was totally redesigned by GM, due to the fact that the block is actually the same that will be going into the 2005 light duty truck lines.
Knock sensors are not mounted in the center valley anymore, they are external. Firing frequencys, internal harmonics and the like are also substantially changed. This would provide for a totally different knock sensor algorithm verses conventional Gen 3 small block.
I hope that this quells some of the debate going on with these new engine designs.
Allthebest, c4c5 :cool
These LS7 classification has been under validation for a while now. The following are fact, as far as changes for the new design.
First, the reasoning for the changes are as follows.
Adding a second intake valve improves intake air flow, which provides some value, but perhaps more importantly the design relocates the exhaust valve and the spark plug within the combustion chamber. The exhaust valve moves from alongside the intake valve to the other side of the cylinder, so less exhaust heat transfers to the intake port. The resulting cooler intake charge boosts power and efficiency.
Positioning intake and exhaust valves on opposite sides of the combustion chamber leaves space in the center for the spark plug, which improves combustion efficiency. Together, these improvements boost power output by 10-15%.
The three-valve engine has the intake valves in a straight line, operating them with a forked rocker arm off a conventional rocker shaft. The solution is a pair of rocker arms. One mounts on the rocker shaft where the exhaust rocker arm would be on a two-valve engine. Instead of acting on the valve, however, the first rocker pushes on a short, nearly horizontal pushrod that runs across the head to a freestanding stud-mounted rocker arm. A short, nearly horizontal pushrod links the intermediate rocker arm located on the conventional rocker shaft to the stud-mounted rocker that opens the exhaust valve. A forked rocker arm operates both intake valves. This second rocker arm pivots the movement into the right direction for the exhaust valve.
The three-valve heads are about 1 in (25 mm) wider than the two-valve heads, but they maintain the low profile that is an advantage of OHV engines. The new heads will work with the displacement-on-demand (DOD) cylinder-deactivation system that will arrive on the two-valve Generation IV engine.
"The three-valve design adds complexity but uses the type of components with which GM is very familiar, so reliability shouldn't be a problem," said Frederick Rozario, Development Engineer, Advanced Powertrain at GM. "And while the added mass in the valvetrain might seem to be an obstacle to high rpm operation, the Corvette engine will rev to 7000 rpm with a 30% margin of safety. It can go to 8000 rpm safely," he added. A special jig will hold the parts together so the whole valve actuation assembly can be installed as a unit on the head. "A weakness of single camshaft engines is the inability to separate intake-cam timing from exhaust-cam timing for maximum efficiency and minimal emissions. But a cam phaser that adjusts the advance or retard of even a single cam, depending on conditions, is still very valuable,"
"The cam phaser on this engine provides 80% of the benefit of a system with separate intake and exhaust phasers." The phaser mounts under the water pump in the traditional timing chain location, so it does not require any additional space underhood. The water pump is new too, because the higher-output engine increases the demand for cooling. The 6.3-L version of the engine will produce 500 hp(373 kW), for example. So the new pump produces twice the 80 gal/min (300 L/min) of coolant provided by the two-valve engine's water pump. The V8's is a two-phase oil pump, switching between high and low flow as needed to maintain the necessary oil pressure without suffering excessive parasitic losses when lower pressure is sufficient The engines also feature optimized exhaust manifolds with equal flow runners for each cylinder.
The exchange factor between c5 and c6 has been theorized alot. Fact is that the oiling system of these engines was totally redesigned by GM, due to the fact that the block is actually the same that will be going into the 2005 light duty truck lines.
Knock sensors are not mounted in the center valley anymore, they are external. Firing frequencys, internal harmonics and the like are also substantially changed. This would provide for a totally different knock sensor algorithm verses conventional Gen 3 small block.
I hope that this quells some of the debate going on with these new engine designs.
Allthebest, c4c5 :cool
