is it possible to replace a 90 hp alh engine with any other in the range,it is in a 2001 octavia.

It would be most straightforward to change it for the 110bhp 1.9 TDI as used in the Elegance as that's the same generation of engine.

I'm not sure what differences there are if you went for a newer PD100 or PD130 version of the 1.9

Welcome to Briskoda

Rather than swap for the 110, just swap the working parts from the 110 to the new engine - i.e the nozzles and the turbo. might need some other bits too possibly.

Or just remap it

Chris

Welcome.

As Chris, says, don't bother to replace the engine. A decent custom remap will have you looking at about 120 bhp, and close to 200lbft of torque, which is slightly more than the 110 makes, and is way less hassle (and expense if you use new parts, or risk using pre-owned ones).