Basically this is only needed if you have your rail pressure turned up and have the oppertunity to blow the relief valve. You will see no change if you have not blown the relief valve. It is not capped on my truck, I do not need it capped yet since I have not blown the valve. You can spend the few dollars on this cap, or buy a new relief from Dodge that is around $400 iirc, or get a solid bolt made for around $25 iirc. My choice is to do this, just a personal perference. If you are constantly experiencing high rail pressure and you cap the relief valve it very well could cause something down the way to give up. Note the disclamer at the end of the origional post.