Ford DOHC I4 Sierra Tuning Guide
It’s commonly believed that this engine is merely a Pinto with a twin cam alloy head bolted on, much like the Cosworth YB. Well, it isn’t, the only thing this engine has in common with the Pinto is that it replaced it in the Sierra in August 1989. Rather confusingly, it’s called an I4, which is also the code name of the current Duratec HE although again, it has nothing to do with that engine either.
Available in two basic versions - 8-valve Sierra / Scorpio and 16-valve Escort RS2000 Mk5 / Scorpio, the I4 has chain driven cams, a cast iron block and an alloy head with hydraulic tappets. It’s a pretty robust unit where every component is built nice and chunky - the cams look like they’re on steroids, whilst the flywheel is a whopping, heavy component.
Basically the engine is meant as a cruiser, especially in 8-valve format although it can be tuned to give reasonable power. The RS2000 engine came with 150bhp and it has seen as much as 230bhp wrung from its bores.
Not a particularly popular choice then, there is little available in the way of performance parts apart from complete induction swaps on RS2000 engines to the likes of throttle bodies and twin DCOEs. Good gains can be made but the engine is harder to tune especially when more straightforward engines are available.