My wife is concerned about the potential for the "money-shift" (downshift over-rev) in her MCS. We have an E36 M3 that can be severely damaged by this type of accidental shift because it is an "interference engine", i.e., the valves WILL strike the piston crowns when over-rev'd, doing horrible things of course.

My guess is that the MCS with lower compression is NOT an interference engine and would not suffer the same valve/piston damage as the M3 (not to say it would not be damaged in some other, less fatal, way). Is this correct or am I wrong?

 

The MCS is a pretty low-compression engine, but that doesn't mean it isn't an interference engine. The VW 1.8T is less than one compression point higher, but still is an interference engine. There are lots of factors like piston shape, valve angle, valve lift, etc. to consider.

Even if the MINI engine isn't an interference one, exceeding the design rev limit can cause other problems like broken connecting rod bolts, etc. The simplest solution is to not downshift when you are close to the rev limit in the current gear.

 

small bore = close valves. If you float a valve they're probably going to touch.

--
Cheese

 

I agree with Andy. Over-revving ANY engine interference or not can cause some serious issues. The best insurance is to not over-rev the engine. If you have a problem or think you may have an issue with selecting the wrong gear then you need more miles under your belt. FYI, most trannies will let you know if you're trying to do something stupid. Don't slam the tranny into gear. If you feel a strong resistance in the shifter when trying to d/s try the next higher gear.

 

We call that mechanical over rev where I hail from and there is not a g.....d thing you can do about it other than use your brain........with ANY engine.......