It's interesting that this thread comes up as I am about to arrange for a mandrel bent stainless in the coming month. It was suggested to me that a 2 1/4 would be sufficient as I will have light mods (mild cam, extractors possibly higher compression pistons). I was leaning towards a 2.5 inch and am now solidly confused... and I have done a fair bit of research!

Oh, and in case you were wandering - I have a B20A gold top engine - the original JDM B20A made for the 2nd gen prelude