ORIGINAL: earlwb

It depends on the engine. The smaller engines tend to benefit from more heat being kept in to aid in combustion whereas the larger engines need some cooling fins to help take some of the heat away so there isn't too much heat being kept in the engine.
I would suggest just trying it and see what happens.
If the engine starts to detonate a lot after it warms up, and you wind up having to back off the compression a lot, then you probably need more cooling fins.