1. Are turbo and non-turbo engines the same? If I found one that was a turbo, would it be the same engine if I removed the turbo?

No, the turbo engines are "beefed up". If you removed the turbo it would need a non-turbo injection pump, but would then be just a overdesigned non-turbo engine

2. Is the 4 cylinder in a 190D the same as the 240D?

no

If you want speed I would go with a 602, 603 or 606, if you want simplicity (and a more "vintage" looking engine), go with a 616 or 617.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine