For one thing, going with a high-output 1.5-liter engine was a matter of affordability and which team developed the car. While it may have been possible to detune a Type R 2.0-liter engine, the cost would have still been high to use the engine, even in low-output form. Honda wanted to keep the price tag affordable. In addition, the Si, a North American car, was developed by the American Honda team with the standard sedan and coupe, both of which are primarily designed for the US. The Japanese team handled the hatchback and Type R, and decided from the get-go they would focus on the 2.0-liter turbo engine. Adams told us that the team in Ohio working on the sedan and coupe spent most of their time with the 1.5-liter engine, and knew that they could get more out of it. The result is the engine you know now, and the power comes mainly from a different turbo map and more boost pressure. The internals are effectively the same as in other turbo Civics.
There's one more reason for the lower output. According to Adams, the car isn't designed to be exactly like more powerful options such as the GTI and the Focus ST. He described the car as being "a different flavor of performance" and that it's meant to feel more nimble and precise, something he said is associated with the Civic Si line. The reduced weight of the Si should support this, too. Adams said the new Si is lighter than the previous generation, but he wasn't able to disclose an exact number. If it is in fact lighter than the 2015, it will come in at under 3,002 pounds. In comparison, the Focus ST weighs 3,223 pounds. The GTI generally matches the 2015 Civic Si with the two-door at 2,972 pounds and the four-door at 3,031 pounds.
It's going to come down to driving it, of course. But like with the latest Miata, a newer, lighter car can be just as fun or more than the car it replaces even if it doesn't have an 840-horsepower Hemi. We'll see if that's the case with the new Si as well.