If you lower compression but leave everything else the same...

1/ Brake Thermal Efficiency rises against Brake Horse Power.

2/ Fuel consumption rises against Brake Horse Power

3/ Exhaust gas temperature (energy) drops against Brake Horse Power

4/ Smoke density drops against Brake Horse Power.

Basically dropping the compression makes for a cleaner burning, less NOx producing, more thermally efficient, less fuel efficient, less powerful engine.

The turbo diesels are slightly lower CR than the non turbo, to allow for the turbo boost.


Basically from all the signs matey's turbo is shot. Either the unit itself or the plumbing, but he is running lower than spec compression.

Compression test won't catch it.

Take the car to a turbo specialist.