is this a goodthing to do for the g? and whats the main purpose?

 

prevents heating the throttle body/neck of plenum with hot coolant. Not needed in warm climates so you can run the plenum marginally cooler bypassing the coolant flow. Motordyne sells a kit...

 

cant you just make on yourself?

 

Yes, you just need to bypass the TB. Connect together the two hoses that go to it and you are done. GL!

 

Unfortunately the air at WOT is traveling so fast that it doesn't have time to heat up from the walls of TB or plenum.
If you can develop a method to actually drop air temperature 11F it might be worth 1% density increase.

A cold plenum can condense more PCV gases/oil vapor after throttle plate making things dirtier and risk thottle sticking.

 

this is true... as I've noticed with excessive build-up (I clean it every so often)… for this reason a “control” valve like Motordyne sells is a better option than completely bypassing… I run with mine open for a while every now and then.

However, a good oil catch can should keep the "PCV oil vapor" to a minimum.

 

not gd in cold weather