4WD MODIFICATIONS - TECH TORQUE
The LandCruiser 300 Series introduced the ‘hot vee’ diesel to Australia. In this short story we explain what that means.
In nearly all petrol and diesel vee engines the induction manifold is in the centre of the vee and the two exhaust manifolds are on the outsides. In the early days of petrol vee engines that was the obvious way to set out the engine, with the temperature-sensitive carburettor and fuel lines nestled in the centre of the engine and the hot exhausts well out of the way. That layout also meant that exhaust heat was quickly shifted out of the engine bay, under the vehicle.
Reverse-flow Ferrari 312 GP engine
That traditional layout remained mainstream, until some rear-engined single-seat racing cars were designed with ‘reverse flow’ cylinder heads. The aim was to get exhaust heat away from the rear underside of the car, where it upset aerodynamics. Instead, a ‘spaghetti’ layout of exhaust pipes was centralised in the vee and piped centrally out the back.
In the days of carburettors that would have posed some plumbing problems, but fuel injection solved that issue.
Porsche hot vee engine
When turbocharging became popular and, later, necessary, for emissions compliance in the case of powerful petrol engines, there was a return to ‘hot vee’ engines by some high-performance engine makers – notably General Motors, BMW, Mercedes-Benz and Porsche.
The rationale was the ability to locate a single turbocharger, or two turbos, close together and to feed into an almost integrated diesel particulate filter (DPF). In contrast, a conventional vee engine had a turbocharger located on the outside of each cylinder bank – widening the engine considerably – and needing a longer pipe run on each side to a single DPF, or twin DPFs. (DPFs work best when close-coupled to the hottest part of the exhaust system.)
Diesel ‘hot vees’
Ford 6.7L Power Stroke engine
Some Australian technical writers have expressed concern with Toyota’s move to a ‘hot vee’ engine for the 300 Series, but the principle has been well proved. There have been several experiments with reverse-flow diesel vee engines, but the first series-production ’hot vee’ diesel was Ford’s Power Stroke Scorpion V8.
After years of using Navistar’s conventional but troublesome V8 diesel, Ford designed its own engine for the 2010 model year. Originally rated at 290kW/997Nm, the 6.7-litre has been progressively upgraded to 354kW/1424Nm by 2020.
Millions of these engines have been produced and they have a strong reputation in the USA.
Since 2010 the Power Stroke has employed several changes to its variable geometry turbocharger. Intercooling is by an air to coolant system that is separate from the normal engine cooling system. It also boasts aluminium cylinder heads and individual rockers for each of the 32 valves.
Toyota’s 300 Series V6 diesel has two sequential turbochargers, instead of the Ford’s single blower. Like the Ford, the Toyota engine has an air to coolant intercooler, but it has twin overhead camshafts per bank, instead of a single block-mounted camshaft, pushrods and rockers.
As conceived, the Toyota 300 Series engine should have no inherent issues, but time will tell…