This was always my major gripe with the Zed. I'm afriad it's due to not using light weight materials. The engine isn't so much the issue as it's an all alloy unit, just the rest of the car. Light weight exotic materials cost money, that's why the Zed is so cheap.
By comparison my BMW is only 10% heavier than a Zed and that's got a big V8, 4 seats and about a foot longer. This is due to Alloy doors, plastic wings and boot plus an all alloy chassis.
BTW my Cossie weighs in at 1217 kg. That's not by using exotics materials, it's due to not having many extras, e.g. air bags and a bendy flimsy chassis with no crumple zones etc.