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There's a vehicle whose engine is 1332cc which produces 94 hp in its home country. It was recently launched in my country with the same engine, but they downsized it to 1299cc (91 hp) for tax benefits. The torque of the engine is the same.

I was thinking what are effects of downsizing the engine can have? Keep in mind, the engine is exactly the same. I am not sure how the manufacturer downsized it.

The two things that came to my mind were slightly lower acceleration, improved fuel economy maybe?

Update:

  • I understand 3 hp difference may not be noticeable, but suppose the power difference is slightly bigger. Then what effects can it have?
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3 Answers 3

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A simple view:

force = mass * acceleration

horsepower = force * velocity

Given the same car, if you decrease the horsepower by 3%, in general, especially if you are talking about speeds under the point where aerodynamics take a significant effect, you are either going to reduce the acceleration or velocity or both.

The internal combustion engine, ICE, is largely an air pump, so if you have a smaller displacement and the RPM, engine design, engine controller, transmission design, etc. stays the same, you will pump less air. You will use less gasoline given the 10% ethanol gasoline, the stochiometric ratio is about 14 to 1. 14 parts air by mass to one part gasoline. You are pumping less air, so you need less gasoline.

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3 hp less?

Not much difference.

As to how, then that is probably a change of stroke which changes the swept volume.

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  • Yes, 3 hp may not have noticeable difference. Suppose the power difference is slightly bigger. Then what effects can you think of in that scenario?
    – ifadey
    Commented Aug 2, 2021 at 15:08
  • @ifadey this is not a discussion blog.
    – Solar Mike
    Commented Aug 2, 2021 at 15:16
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    More than likely, they've downsized the bore, not the stroke. There's a lot less to it than changing the stroke (where you'd have to worry about rod length). Just changing the piston diameter is pretty easy (yes, the rings would need changed as well). But I guess it's all theoretical and could be done either way.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 2, 2021 at 15:29
  • @Pᴀᴜʟsᴛᴇʀ2 some stroke changes just involve a change on the crank...
    – Solar Mike
    Commented Aug 2, 2021 at 15:34
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Keep in mind that different jurisdictions have different methods of measuring the engine power (and in some cases, displacement - even if one could think it is a simple geometry).

Different regulations dictate differnt constraints over the engine operating envelope - the engine may be derated by these 3hp in order to get into the local eco norms.

Some cc are lost (or gained) in the conversion between cubic centimeters and cubic inches as well. People like round numbers and one doesn't get a round number by multiplying by 2.54 three times, no matter what the other number is.

It may as well be that the engine is exactly the same.

On the other hand, these ~3% difference in power are less than the usual difference between the day and night (because of the different temperature and air density). Winter/summer can be even more.

You don't feel your car is more powerful at night, do you? Because most cars are.

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