Well ....
86mm bore is about the max the M20 will go and I have seen a couple blocks that have had issues with going that big. Overall, if you have your machinist check the block prior then you should be fine, it's just an unnecessary risk to me.
Aside from that it's some simple things
-You can still use a std. headgasket on an 85mm bore, go to 86mm and you relegate yourself to running custom MLS headgaskets (maybe not so much a price issue as it is to be caught out needing a replacement and struggling to find one in a pinch, I've been on the other end of the phone call more than once).
-You will have to run a custom piston alloy that will wear faster or is pretty brittle and not an ideal crown shape. You will still get good use from the engine, just not nearly as long with the pistons I mentioned.
-Not taking advantage of the longer stroke when there would be no difference in price would be like saying "no" to your wife when she looks at you mischievously.
86mm bore is about the max the M20 will go and I have seen a couple blocks that have had issues with going that big. Overall, if you have your machinist check the block prior then you should be fine, it's just an unnecessary risk to me.
Aside from that it's some simple things
-You can still use a std. headgasket on an 85mm bore, go to 86mm and you relegate yourself to running custom MLS headgaskets (maybe not so much a price issue as it is to be caught out needing a replacement and struggling to find one in a pinch, I've been on the other end of the phone call more than once).
-You will have to run a custom piston alloy that will wear faster or is pretty brittle and not an ideal crown shape. You will still get good use from the engine, just not nearly as long with the pistons I mentioned.
-Not taking advantage of the longer stroke when there would be no difference in price would be like saying "no" to your wife when she looks at you mischievously.
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