Still haven't had the chance to drive an E21. This one must be a blast!
https://silodrome.com/bmw-e21-race-car/
"The original 2.3 litre engine has long since been removed and replaced with a larger and higher-performing M20B25 engine. Advanced Tech Automotive imported and supplied the engine, it's now also fitted with a cold air intake system and it was fitted with new gaskets, a clutch kit, a new flywheel, and a new exhaust system including Hi-Tech headers and a performance exhaust system."