13" spinner on a -4?

I was looking to replace my 12" spinner for my 3-blade Catto with a 13" spinner. Has anyone put a 13" spinner on their -4 with a stock cowl? Is the extra .5" going to look odd (i.e. will the extra .5? radius extend past the cowl and if so will it be noticeable)?

We did. We replaced the metal fixed pitch Sensenich with the new Adjustable pitch carbon fiber prop. They offer a 13" spinner only, and our RV-4 is older, and had the 12" spinner.
The 13" spinner is slightly oversized, but I always thought the 12" spinner was a bit undersized, so to my eye it's no biggie. It's only noticable at the top.
I suppose you could blend the cowl to it with some light weight fairing filler...

Do a search on VAF. This has been talked about a few times.

Short answer; I did it on my plane and did not like it. Besides the fact that the spinner is 1/2 inch larger in diameter, the contour of the spinner does not follow the same lines as the old style cowling. No performance degradations or cooling issues were observed.

At the end of the day, if you like it and you are happy, then whatever someone else says (like me) does not matter. Good luck, whatever decision YOU make is the right one.