Winnipeg Free Press - PRINT EDITION
Vette's driving force an updated old friend
The history of Chevrolet's Small Block V-8 engine is mind-boggling.
Introduced in 1955, it has been the anchor of GM's engine lineup and the Chevrolet Corvette's driving force. When it went into production, it displaced 265 cubic inches (4.3 litres), relatively small for a V-8. Remarkably, when the Turbo-Fire V-8 arrived, it was 19 kilograms lighter than the Blue Flame in-line six it replaced!
You name it and a Small Block has likely been that size -- the list of displacements is bewildering in its magnitude. It has been every size, from the aforementioned 265-cu.-in. motor right through to 400 cu. in. (6.6L) and it has touched just about every displacement in between.
The second-generation Small Block debuted in 1992, meaning the first generation had a staggering 37-year run, and displacement aside, it had remained basically unchanged. The second iteration's debut coincided with the production of the one-millionth Corvette, a white convertible.
Since then, there have been a number of generations. The fifth-generation Small Block will debut in the 2013 seventh-generation C7 Corvette when it hits the road next year. It's an important consideration, given that the Small Block has been a key component of the Corvette makeup for the past 57 years.
The latest Small Block is a V-8 that still uses good old pushrods to open its valves and not the twin-overhead cams and turbochargers many had predicted. The new 6.2L, which is named LT1 yet again, is completely new. The only carryover parts are the starter-motor bolts and valve keepers. That's it.
It took more than six million hours of computer time to develop the combustion chamber, the shape of the piston crown and the placement of the fuel injectors relative to the spark plugs within the cylinder.
This was done to ensure the very best fuel economy without giving up on the quest for power. The new LT1 produces 50 pound-feet more torque than the outgoing engine, and it develops the same amount of torque between 2,000 and 4,000 r.p.m. as the mighty 7.0L V-8 that powers the Corvette ZO6.
Now for the all-important numbers, albeit the preliminary figures: The latest Small Block produces 450 horsepower at 6,000 r.p.m. and 450 lb.-ft. of torque at 4,000 r.p.m., which will give the C7 Corvette a claimed run from rest to 96 kilometres an hour of less than four seconds, which is pretty darned quick.
The high output and fuel efficiency (GM claims an average fuel consumption rate of 9.0 litres per 100 km) is due to a number of important factors. This engine employs direct injection, a first for an overhead-valve engine, continuously variable valve timing and a high 11.5:1 compression ratio. The latter is allowed because direct injection cools the cylinder, which prevents detonation and the need to retard the timing to prevent it. Though it does mean the engine prefers premium fuel, it will live on a regular diet.
The cam phasing alters the intake and exhaust opening and closing points in unison over a 62-degree angle. Some will argue this is not as effective as altering the intake and exhaust camshafts separately, as is the practice in modern overhead-cam engines. GM counters that the LT1's system delivers 80 per cent of the advantage associated with cam phasing without the cost and complexity.
It weighs just 211 kilograms. By way of comparison, BMW's 4.4L twin-turbo V-8, which delivers 400 hp and 450 lb.-ft., tips the scales at 228 kg. The difference is the mass the engine places over the front wheels and the effect it has on handling. GM says the C7 Corvette will have less understeer because of the lightweight all-aluminum construction of the engine. Likewise, the compact height allowed the C7's designers to incorporate a lower hood line without impinging on pedestrian-impact regulations.
As for efficiency, the key in a large-displacement engine is cylinder deactivation -- it's the most important fuel-saving device. The new engine will spend a lot of its running life in its four-cylinder mode. GM says this is why it picked the larger 6.2L displacement. When operating in four-cylinder mode, the operational cylinders still displace 3.1 litres.
A smaller-displacement engine may have been more fuel-efficient when all cylinders are firing, but it could not spend as much of the time relying on four cylinders. As it stands, GM claims a 20 per cent reduction in fuel consumption when the engine stops firing cylinders one, four, six and seven. At the heart of the horribly named Active Fuel Management is an electro-mechanical system that bleeds off the oil pressure in the lifters, which then deactivates the cylinder.
As for some of the stuff included, the new engine has oil-cooled pistons, a forged crank and connecting rods and there is an available dry-sump derivative that is better able to withstand the lateral g-forces the engine is subjected to in a track environment.
Finally, the fear a Corvette operating on just four of its eight cylinders would sound more than a little wimpy is a non-issue -- as throttle input is small and the engine loads are low, the exhaust note would be muted anyway.
-- Postmedia News
Republished from the Winnipeg Free Press print edition November 30, 2012 A1
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