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Here's a just-out-of-curiosity question for you tech guys and gals:

I understand that the 1.5L ICE in the HSD Prius is similar to the one used in the US-sold Echo and maybe other Toyotas. I get this understanding from what I've read on this site and from my personal experience of changing the oil on our new Prius and our old Echo: the filters and the ICE around them seem the same.

Okay then. Why does is the Echo engine rated at about 105hp (~6000rpm), whereas the Prius engine is rated at 76HP (5000rpm)? The rpm difference is probably the answer to my question. But I wonder why the engines' hp are rated so differently? One guess is that their output is the same, but that as part of managing fuel consumption, the Prius's hybrid system won't allow the ICE up into the upper rpm's because it'd be inefficient.

Any insight or explanations? Thanks!
 

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ICE's hp rating is not just a function of their size of their cylinder displacement. Given the same size engine, the HP rating can differ significantly depending on the valve timing, ignition timing and stoichiometric chemistry (mixture of fuel and air.) My understanding is that the Prius engine is tuned for maximum fuel economy and minimum emission and with power output as a secondary consideration. I think that's what accounts for the hp difference.
 

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Where's my HP, dude?

Mostly commonly explained as Atkinson/Miller combustion cycle. Prius achieves this by varying the intake value timing, so that there can be some overlap between the opening of the intake and exhaust valves. Advantage = increased therodynamic efficiency over a wide range of rpm. Disadvantage = reduced torque at low rpm. Less torque is compensated by assist from the electric motor MG1.

Is the Echo ICE permitted to exceed 5000 rpm? I really don't know.

DAS
 
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