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  • William Maley
    William Maley

    Toyota Not Following Everyone Else With Small Turbo Engines, Sticking With Large Displacement Engines

    William Maley

    Staff Writer - CheersandGears.com

    October 17, 2013

    The trend with powertrains is to do small-displacement engine with turbochargers to provide the performance of a larger engine with the fuel economy of the small engine. Toyota looks to be bucking the trend.

    In a interview with Automotive News, Koei Saga, senior managing officer in charge of drivetrain research and development for Toyota said the company will be investing into turbocharged engines, but it will not "emphasize turbocharging across many product lines." Instead, Saga says the company believes that using large-displacement engines with the Atkinson cycle.

    Here's why Toyota believes this is the right idea. Atkinson cycle engines keep the intake valves open longer than a normal gas engine, which cuts the length of the compression stroke and in turn cuts pumping losses. The end result is improve efficiency at the cost of torque. This is why you see Atkinson cycle engines used in hybrid vehicles since the electric motor can provide the low-end torque. When paired with a large-displacement engine, the hope is that you keep the efficiency while gaining back the loss in torque.

    In addition to the large-displacement Atkinson cycle engines, Toyota will invest heavily into continuously variable and fixed-gear automatic transmissions, as well as its fuel-cell vehicle program.

    Source: Automotive News (Subscription Required)

    William Maley is a staff writer for Cheers & Gears. He can be reached at [email protected] or you can follow him on twitter at @realmudmonster.

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    Small displacement + turbocharging doesn't pan out for better efficiency. It never did and it still hasn't. The reason is simple... by going from a 2.0L I4 to a 1.4L I4 you haven't changed the frictional losses that much because you still have the same number of valves, guides, followers, pistons, rods, etc. The main efficiency gains come from having smaller cylinders working at bigger throttle openings which allows the engine to operate at a higher effective compression -- because larger throttle openings equals lesser vacuum and squishing less vacuum equals higher effective compression. But turbocharging mandates an ~2 point reduction in compression ratio while providing no charge density improvements at cruise. This cancels out much of the efficient gains from displacement loss.

    The best non-hybrid efficiency is actually achieved with a large displacement Atkinson Cycle engine with least amount of camshafts, valves and cylinders. If you want the most fuel efficient 140hp you'll use a 2.5L 3-cylinder engine with 17.0:1 static compression and a 70% Atkinson cycle cam for a 11.9:1 effective compression @ peak volumetric efficiency. You'll use a single overhead cam or a in-block cam with roller followers/lifters. You'll use 2 valves per cylinders. And, you'll use direct injection. Apart from DI, you'll basically do the exact opposite of what many automakers are doing.

    In the end, 1.4L Turbo, 2.0L NA and 2.5L Atkinson engines probably have approximately the same output. The 2.5 Atk has the best fuel efficiency whereas the 1.4T has the highest cost and most reliability concerns. The 1.4T is only useful as so far as to take advantage of various countries' displacement tax laws to lower the new car and annual taxes. Whether this is significant depends on the country.

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