I know that they make a 5/16" and a 1/2"...so which is
better..Motordyne makes a basic,
iso thermal, and a copper iso thermal....What
should I go with? and will I really feel a difference?....some opinions please

 

You query might be better served, if you post here.

https://g35driver.com/forums/intake-exhaust-23/

In any event, what model year is your G? A bit more info will afford you much better results.

 

i have a manual 03 coupe sport package

 

Search it. I usually don't like saying that, but this is probably one of the most talked about mod.

Both are good, no such thing as "better". It's just a matter of preference, which most people seem to prefer the 5/16.

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i just put the 5/16 copper iso on mine and i love it. get copper is it ever snows or gets cold in your area.

 

5/16"

 

my preference: 5/16" iso thermal