Keep the stock one, unless you just want your bay to look 'neater'
I was going to get the plazmaman rb20 plenum, but after reading a lot of info about these going onto rb20det it's a loss in power.
Also supposably it bolts straight on BUT other things will get in the way, battery ect.
So I'm sticking with stock, good for 270kw or more. An rb20 probably won't see much more than that anyway..