tooter's manifold adventure...

[tooter]

Originally Posted by Bluevitz-rs

I think you're confusing it with a 2 stroke. Atkinson cycle is the same as Ottos. The only difference is that Atkinson has a shorter compression stroke than power stroke. On the Prius, this is achieved through intake cam timing and duration. The intake valve is held open much longer allowing some of the intake charge to be pushed back on the compression stroke reducing the energy required to compress the intake charge. This in turn rises the efficiency of the engine by effectively making the power stroke longer extracting more energy.

You're right. Hybrid engines acheive the Atkinson effect with valve timing.

Found this by searching How does a Prius hybrid engine work:

"Its engine only runs at an efficient speed and load - In order to reduce emissions, the Prius can accelerate to a speed of about 15 mph (24 kph) before switching on the gasoline engine. The engine only starts once the vehicle has passed a certain speed. And once the engine starts, it operates in a narrow speed band."

The bottom line is that installing a different throttle body on the engine might impair the optimum performance in that very narrowly tuned rpm range.

This explains why they use that weird intake manifold.