I heard on the Bill Handel Show - he said he has a 7 series
BMW and he uses regular gas all the time, he said there is
something about the high performance engine and it switches
over when regular is used. Has anybody out there ever put
regular gas in a 2006 525I ???

BMW cars can go on regular fuel.The ECU can adapt to the fuel u put in your tank.
However I strongly say NO to regular usage in BMW cars.
Your will hear heavy knocking noise in the engine after regular use of less octane fuel.
If you are unlucky,u may land up for major repairs.
Considering the saving and expenditure.You will see a big loss end of the day.

BHS must be having 735 or bigger.In his case the car can still move with 50 per less power.But how it performs.Am sure
the engine otuput power is not as premium useage.

This is penny wise and pound foolish experiment.
So dont try it.

The computer will compensate for the lower octane. However, you should experiment with regular. The reason is that you might find that you get better mileage with the premium.

It won't hurt (as long as it's quality gas) and you might save, but you might find the mileage diff is not worth worth saving a coupla bucks.

haven't owned any bmws. but what does the manual say? if nothing else try using regular. maybe half and half. i use to race my 69 and 70 mach 1s. the 70 would only use 93 octane, it would ping and knock something awful if used any octane lower. but the 69 drove the same whatever octane i used.