The main savings that was to be had with a Rotary was on the production side -- fewer moving parts, cheaper to build and assemble. Fuel efficiency was no better than a piston engine of similar output. There would be a small amount of fuel savings due to less weight, about 2/3 the weight of a typical V-8 of similar output. Hot rodding one is a different story -- not easy to do. Can't just change cams and intakes like a V-8. But manufacturers weren't concerned about that! GM was interested in the production costs savings, as were all others. In the end, GM dropped it because they couldn't get it to meet upcoming pollution standards. They got it to meet early 70s standards (dropped it around 75), but couldn't get it to meet future proposals. So they asked the government for a 10 years freeze just on their rotary, and it was denied. So they just wrote it all off. The real cost savings came from designing a car around the smaller package, not just fitting it in a currently produced car. AMC had a license to build rotaries, but not the capital to do it. GM agreed to sell to them in order to increase production levels for GM, making the engine cheaper to build due to numbers. AMC designed the Pacer around the relatively large (compared to other production rotaries -- Mazda and NSU) GM rotary only to have the rug pulled out from under them. They had done too much work on the design to scrap it , so they made their straight six fit. That's why it sits under the cowl so far and has a big trans tunnel -- it originally had all kinds of foot room in the front.