Octane
 

I've been reading around and most people seem to recommend putting hi-test in their BMW's.

When I purchased my car, it did not come with a manual, and I'm used to putting in 87 octane gas. Through some reading, I see that the M42 is a "high-compression" engine, and further that it does not have a knock sensor.

Am I slowly killing my engine by putting '87 in it?

according to the manual, it can accomodate it, but you should use 89. someone on here only uses 87 i read somewhere.... there's a sticker on my fuel door saying 89, so wtf i run that.

Also there is a knock sensor on late M42 engines. If yours is a 95 then it has it. I think all M42's after (and including) '92 did. Also I use 89 octane and don't have any problems. It is what the manual recommends.

M42 and newer engines have knock sensors and unless you have a supercharger, you should be OK with 89. Superchargers call for 93 but in CA you have to settle for 92 which seems to be OK.
Gary

Since OCtane ratings are +- like 10% It makes little difference between ratings.

My 95 runs fantastic on 87, No issues, It runs cooler on long highway runs at higher speeds with 92, But pinging has never been a problem.

Dave