Why did bmw take a step backwards in 1987?

[massive]

Can anyone explain why bmw lowered the compression in the M20 engines when they facelifted them

Is there a reason for this step backwards?

[E30BeemerLad]

think it was to do with emissions and cats etc but may be wrong.

Possibly also that their crystal ball saw that petrolheads on the zone may want to turbo

[ed325i]

Yes it was to do with cats.
ED

[blingsta]

what would explain that mines an 89 and has no cat??

[E30BeemerLad]

cats were an option in the UK I believe, until they became compulsory in 1992.

American market they were compulsory from mid/late 80's I believe

[Dan318-is]

Early engines also were designed to run on four star, not unleaded. People running them on unleaded often experienced high combustion temperatures and often pinking. This caused the exhaust valves especially to become extremely hot and be subject to pitting on the valve head itself. Most valves were replaced under warranty im told

whether this is to do with the lowering of the compression ratios or not i dont know, but its food for thought,

[Simon13]

cats became compulsory in germany at this time, for everywhere else it was offered as an option like the uk.

Back then they couldn't get engines to make the same power with cats fitted or keep the compression as high.

This is also why 2 piece exhausts appeared on facelift 325i's, so in the factory when cat option was ticked the front section was replaced.

[klobuznik]

It has to do with fuel consumption, cats and engine electronic management introducing MOTRONIC insteda of JETRONICs...
Therefore after reestying: Less power but also less fuel consumtion and higher efficiency....