The Falcon 9 has 10 engines. One nine-engine first stage and a single engine second stage.
The Falcon Heavy has 28 engines. Three nine-engine cores and a single engine second stage.

SpaceX should soon be pretty perfectly recovering the first stages and the fairing and other parts. Only the single-engine second stage will not be recovered.

If 2018 production was 400 engines. Then ten Falcon 9 and ten Falcon Heavy could be produced along with extra single-engine second stages.

In 2018 and 2019, SpaceX could produce twenty reusable Falcon 9 and ten Falcon Heavy's along with 220 expendable second stages.

There are currently only a handful of Falcon Heavy launches on the manifest. Although Elon Musk has mentioned they have a dozen commercial customers for the Falcon Heavy.