(August 31, 2009)  After more than two decades of offering optional diesel engines made by Navistar in its heavy-duty trucks, the 2011 versions will get an all-new Ford developed V8. The new diesel which had been code-named Scorpion features a reverse-flow layout for the first time on a diesel engine along with a novel new turbocharger.

The biggest architectural change for the new engine is the reversal of the usual arrangement of the intake and exhaust manifolds. Traditional V-type engines have the intake manifolding and fuel system in the valley between the cylinder banks with the exhaust manifolds on the outboard side of the cylinder heads. Virtually all modern diesel engines are turbocharged and this intake-exhaust arrangement is not optimal for turbocharging.

With a single turbocharger setup, the exhaust manifolding has to be run either around the ends or over the top of the cylinder heads. This configuration contributes to turbocharger lag since the exhaust gases have to travel further to get to the turbine and spin it up.

Ford has used the same concept that BMW has implemented on its new 4.4-liter gasoline V8 by turning everything around. General Motors also incorporated a similar configuration for the 4.5-liter light duty V8 it had developed for 2010 introduction. That engine has been put on hold pending an uptick vehicle sales.

Putting the exhaust ports on the inboard side of the heads with the turbocharger in the valley. This allows the runner length to the turbocharger inlet to be extremely short. From the compressor outlet, the intake charge flows around the end of the cylinder heads to the outboard manifolds.

The second innovation that Ford has incorporated to minimize turbocharger lag is a new type of turbocharger from Honeywell. Because a turbocharger spins at speeds up to 100,000 rpm, rotational inertia affects response. Some engines use a small turbocharger to provide quick response but this limits top-end gas flow. An alternative is a sequential dual turbo setup that diverts the exhaust gas flow to a larger turbo as speeds climb. This adds to plumbing complexity and cost.

The new design from Honeywell uses two smaller diameter compressors mounted back to back on a single shaft to reduce the effective radius and inertia. This should allow faster spin up while accommodating the necessary air flow for maximum performance. Also benefiting the performance is a valve-train with four valves per cylinder. In order to help keep overall engine size and mass down, Ford has opted for a push-rod arrangement with a cam-shaft in the valley of the engine block.

Ford claims the overall arrangement not only improves performance but makes the engine much easier to service. The turbocharger arrangement on the Navistar engine requires removing the truck cab from the frame to service it. The top mounting of the new engine allows everything to be serviced from under hood.

In order to improve fuel efficiency, refinement and emissions performance, Ford has incorporated the latest Bosch common rail fuel injection system. The Scorpion uses a 30,000 system pressure with piezo electric injectors. The eight hole injectors can execute up to five injection pulses per combustion cycle. Using multiple pulses allows the power delivery to be spread out, reducing noise and combustion temperature. The lower combustion temperature results in reduced production of NOx.

The fuel system alone is not sufficient to meet Tier 2 Bin 5 standards so Ford's new diesel uses a complex after treatment system like most other modern clean diesels. The first stage is an oxidation catalyst which reduces unburned hydrocarbons to water and carbon dioxide while also raising the exhaust gas temperature. Raising the exhaust temperature helps improve the effectiveness of the next two stages.

The second stage is a selective catalytic reduction system (SCR) that injects an aqueous urea solution into the exhaust stream. The heat of the exhaust converts the urea into ammonia that reacts with the NOx in a catalytic converter. The NOx is converted to water and nitrogen. The final stage is a diesel particulate filter to eliminate most of the soot emissions.

Ford has also put significant effort into reducing the mass and improving the durability of the new diesel. Ford and Peugeot pioneered the use of compacted graphite iron (CGI) for engine blocks for the 2.7-liter V6 they jointly developed and introduced in 2003. Since then it has been adopted by Audi for its V8 and V12 diesel engines. CGI has twice the strength of gray iron allowing the block walls to be made thinner and thus lighter without sacrificing durability. Another mass reduction factor was the use of aluminum for the cylinder heads. The heads get dual water jackets to ensure they don't overheat.

Ford's new diesel joins the updated 2010 version of General Motors' 6.6-liter Duramax in being fully compatible with the new standardized B20 biodiesel blends. This is a distinct change from the current engine with has had numerous field reports of damage to the diesel particulate filters when running on B20.

Ford has not yet announced specific figures for the new engine although it claims the new engine will beat the 350 hp and 650 lb-ft of the 6.4-liter Navistar engine. The new diesel which will retain the Power-Stroke badge will debut in updated 2011 Super-Duty pickups.