The cylinder heads on the 4.5L are like nothing we've seen before. Check out the curved in
Diesel Power:
For a diesel engine, the 4.5L LMK seems small, as in both narrow and short. It's said to fit pretty much anywhere a small-block Chevy will fit, is this true?
Charlie Freese:
Yes. As you mentioned, the engine is quite compact. This was achieved through a few key design decisions. We selected a 72-degree bank angle, rather than a more traditional 90-degree V-8 configuration. The block material is compacted graphite iron (CGI), which allows us to do some interesting things with the bottom end that stiffen the structure and reduce engine height. We eliminated the outboard manifolds, making the engine narrower. The inboard exhaust arrangement allows turbochargers to package close to the exhaust ports and provides space for a closely coupled oxidation catalyst. This is an essential part of the new emissions aftertreatment system. By keeping aftertreatment hardware close, we can warm it up and light it off quickly. This enables a clean diesel with better fuel efficiency. These design characteristics allow the 4.5L V-8 Duramax to fit into about the same packaging envelope as a small-block gasoline engine.
From the top, you can see where the runners curve up and end in the intake ports. In case
Diesel Power:
With diesel and gasoline up over $5.00 a gallon, fuel mileage is a big concern. How will this engine compare to a similarly equipped gasoline engine as far as fuel economy goes? Any idea on how much of a premium people will have to pay for the 4.5L diesel?
Charlie Freese:
We expect the 4.5L V-8 Duramax to deliver about 25% better fuel efficiency than a comparably powered gasoline engine under light load operation. However, when the truck is used for work (towing and hauling), its fuel efficiency advantage extends into the 40-70% range. Think of this as a situation where you are towing a heavy load over a mountain. That is where the diesel best demonstrates its advantages. Naturally aspirated gasoline engines must run richer and go into catalyst protection mode. A diesel does not. We have not announced option pricing for the new 4.5L Duramax. It is still a little early for that.
On the exhaust side there are no ports, just a couple of outlets where the exhaust will co
Diesel Power:
There are a lot of different details within the 4.5L LMK that people might not notice; such as the cam arrangement, valvetrain, head flow characteristics, balance shaft, EGR cooler, compression ratio, and injection system. Tell us a little bit about those.
Charlie Freese:
Sure. To start with, the 4.5L employs a four-valve-per-cylinder DOHC architecture. This provides a very stiff valvetrain for efficient operation over a wide speed range. Hydraulic lash adjusters deliver maintenance-free operation with very low noise. Camshafts are chain driven from the front of the engine. Engine breathing is another place where inboard exhaust offered interesting design options. We eliminated intake manifolds by porting the intake down through rocker covers. Air enters the cylinder heads from above.
This eliminated parts, narrowed the engine, avoided leak paths, and reduced engine mass. Because exhaust ports exit toward the engine's valley, we shortened the passages into the turbine and the exhaust gas recirculation system. This approach better manages thermal energy and lowers fluid flow losses. By retaining more exhaust, gas heat, turbocharger, and oxidation catalyst performance are improved. Because we selected the 72 bank angle, this engine uses a single-balance shaft low in the block. We selected a rear-mounted nodal chain drive to minimize torsional vibrations. Considering manufacturing tolerances, a 72 V-8 engine can actually deliver better balance than a 90 engine.
The EGR cooler package is another interesting area. With all the exhaust components centered in the valley, we can more easily plumb the EGR system. Cooler, valves, and pipes are efficiently located with minimal cost, mass, and space penalties. The 4.5L operates with a 16:1 compression ratio, which supports our fuel efficiency, emissions, and durability objectives. Cold start requirements are satisfied using glow plugs, an air intake heater, control software, and proven practices from the 6.6L Duramax.
The fuel system is a high-pressure common rail. Peak injection pressures are set at 29,000 psi. Injectors are piezo-controlled, allowing multiple injections, precise fuel metering, and minimal dwell times. We can inject multiple pilots, split the main injection event, and achieve multiple post injections for optimal combustion and aftertreatment performance.