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I want to verify this, supercharging my fj would not benefit me in mud ridding even though it would be nice to have the power to push the 35s
A TRD type supercharger requires higher RPM than a URD type in order to generate power to overcome the parasitic loss of the belt/gear and screw/fan it needs to spin, and to be able to compress enough air to give you good performance.
Short answer - probably not very much benefit. Read the centrifugal supercharger writeup below.
'Roots' supercharger (TRD)
Twin screw supercharger
Centrifugal supercharger (URD)
More supercharger information.
Basic - Supercharger Basics
Advanced - Part 1 - Superchargers A-Z (Part 1 of 3)
Advanced - Part 2 - Superchargers A-Z (Part 2 of 3)
Advanced - Part 3 - Superchargers A-Z (Part 3 of 3)
More info on centrifugal (URD type) supercharger - The Centrifugal Supercharger Explained
Superchargers (these days) are quite reliable and resilient.
There are a couple places where the type of supercharger needed for our off road activities would cause some problems.
A gear driven twin screw supercharger (Whipple for those of you who are familiar with them) would need some way to blow off back-pressure when you rev the engine to get out when stuck. The URD (and I presume TRD) one, since it is centrifugal and a fan type, will allow this pressure to flow back over the fan without a problem. As far as the engine goes, very high rpm is what causes problems and so no worries there.
I *might* suggest very closely logging your engine specs without the supercharger and seeing what kind of use you are putting your truck to. Then, after getting the supercharger installed I would see about getting a custom PCM tune made for it. (Note: URD might offer this I do not know.)
Check into an upgraded fuel rail. Not a lot of use to have more air in there if you can't feed in enough fuel.
ABSOLUTELY check into beefing up the following things:
Optional but advised
As Air2Air mentioned, you probably want to upgrade the transmission itself
if you are using this for highway and more speed, brakes, BIGGER ONES!
spark plugs - I always advised getting a 1 range colder as you are pushing denser, colder air into the system and as such your combustion chamber temp will be a little lower, plus it helps a little to control any tendencies to pre-combustion. (this is a BAD THING*)