Tuesday, April 15, 2008

A peek inside Chrysler's new HEMI

By Justin Pritchard,

Chryslers updated HEMI V8 makes more power using less fuel. How's that work? Pritch asks the engineering team for a closer look.

The 2009 Ram is nearing launch, and a recent powertrain update sees its 5.7-liter HEMI V8 more powerful and efficient than ever before. Horsepower is rated at 380, a ten percent increase, while torque peaks at over 400 lb.-ft.

2009 Dodge Ram

It's also less thirsty than the outgoing model. Truly, it's probably never been more environmentally friendly to run a truck with enough torque to pull a tree out of the earth's crust. But how do engineers create more power with less fuel? And how much better on fuel could the HEMI actually be made, anyhow?

According to Chrysler, making more power with less gas has a lot to do with breathing. Imagine an engine as being similar to an Olympic runner. For either to achieve top performance, a huge volume of air needs to make its way in and out easily- and any restrictions can have a negative effect. Imagine the runner trying to race while breathing only through their nose, for instance.

The air intake system of an athlete is less physically complicated than that of a HEMI V8, but it remains that opening things up in the name of airflow can bring positive benefits. Additional power for the new HEMI was achieved primarily through three areas: reduced air flow restriction, an active intake manifold, and Variable Valve Timing (VVT).

Head ports, the engines equivalent of a windpipe, were redesigned using a sophisticated computer which helps engineers determine their optimal shape and size. They've even gone so far as to use a finer grain of sand in the casting process, which improves the surface finish inside of the head ports themselves. The valves have been made larger too- all in the name of allowing the air-fuel mixture in and out of the engine more easily.

The variable intake manifold is able to switch between different 'runners', which are passageways that air is drawn through on its way into the engine. A flap-valve directs air into the powerplant from one of two runners- depending on the situation. Longer runners aid low-RPM torque, while shorter runners rush air into the engine for high-RPM horsepower. A single manifold represents a compromise- but the variable unit allows for a performance-oriented manifold and a more economical manifold to occupy the same physical space.

Variable Valve Timing, (VVT), manipulates the valve timing to operate the engine in the most efficient manner for the situation. For instance, by closing the intake valve later, the engine has to do less 'pumping' as the piston travels down on the intake stroke. Optimized exhaust valve timing allows more of the combustion energy to be transferred to the crankshaft, rather than simply ejected as heat.

Chrysler's Multi-Displacement System (MDS) in on board as well- saving fuel through cylinder de-activation when full power isn't needed. Chrysler engineers estimate that MDS has saved about 100 million litres of fuel since hitting the road in 2005. For 2009, MDS has a wider operating range and an indicator light in the information display to tell drivers when it's engaged.

All said and done, fuel savings are in the neighborhood of 4 percent- respectable considering the extra power. Thing is, I was left wondering just how much more fuel-efficient he HEMI engine could be made. Is the new one as good on gas as it can ever be? Is there some technology or system that a gas engine can employ to save significantly more fuel, but that isn't affordable yet?

Chrysler's team says that they're reviewing technologies that can improve fuel efficiency of current engines by another 10 to 15%. Trouble is, they're very expensive and need to be introduced in low volumes to gage customer response. A technology that can save $1,000 worth of fuel won't sell if it costs $2,500.

That said, will the world ever see gasoline-powered full-size trucks get 50 miles per gallon? Or is some mathematical minimum amount of fuel needed to make a full-sized truck move?

Chryler's engineers say that there is a theoretical limit for fuel consumption in a full size pickup with attributes similar to those sold today- and that it's considerably less than 50MPG. Not to say that it's impossible- but the vehicle would need to be considerably lighter, far more aerodynamic and offer a huge reduction in rolling resistance, as a start. These attributes would come at the cost of strength, size and traction, which are vital for a pickup.

It was an interesting question nonetheless, but it still looks like today's consumer will have to take their fuel-savings a few percent at a time. The 2009 Ram HEMI goes on sale later this year.
Photos: Chrysler

No comments: