Will it hurt my engine if I put regular gas in my 6 year old BMW?
Possibly. You will lose MPG and some power of the engine.
1: Your owners manual will either say “premium required” or “premium recommended”. Which is it?
2: What do you hope to achieve by putting regular in vs premium?
Question 2 is perhaps the most important. IF you can run it on regular without damaging it (re Q1), then the mileage will drop. If it drops enough to make up for the cost difference between regular and premium (which isn’t really all that much), then you’ve saved nothing, and lost the fun factor at the same time.
There’s some math involved. If you can do regular, give it a shot and see what it gets you.
Please search for the hundreds of existing threads asking this same question. The answer is the same for you.
I have found that either fuel nozzel fits quite well,so fill her up with what ever you chose, (M cars excluded)
You bought an expensive performance car. BMW designs its cars to use premium fuel, it also recommends top tier gas. Using cheap brands of fuel and low octane fuel means you are willing to accept the risk of damage to your expensive car.
Your car has a knock sensor to protect it from damage due to low octane gas. But, you are depending on that knock sensor to work and in extreme conditions even the knock sensor cannot fully protect the motor from pre-ignition. Holes in pistons can lead to an expensive motor repair.
If you are willing to risk an expensive repair to your expensive car you can use all the regular gas you like.
So you can save, what, $4 at the most each fill up?