I have heard of as high as 230, and my car (2.0L) is running great at 180-185 on all 4 cylinders... and I'm lining up parts for a ring job to coincide with my P&P head installation. An engine will keep running smoother and smoother (and weaker) until the mid-100s and even then it will probably keep going as long as the top end is sealing up. It would probably be gutless though, and the oil would get nasty in a hurry with all the blowby.
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