Originally posted by spanky250
When FMF first came out with their "offroad" line of pipes with heavier metal, they were called "Burly". For some reason, probably because some marketing guru said it would sell better, or maybe it sounded more "manly", they changed the name to "Gnarly". It is still the same pipe.
Per FMF's advertising, the Gnarly is 2 gauges thicker steel than the Burly.
Since they only make one pipe for some bikes, and choose to make it in one thickness like the Gnarly, people confuse the thickness name with what the bike is supposed to do to the power. In reality it varies by bike model, and in some cases (like with the KDX) they make multiple pipes for the same bike, both called Gnarly nowadays. I believe the 30 and 35 designs were around before even the Burly designation.
As for the '89-'94 bikes, a "Fatty" is available. It would not surprise me if that pipe is currently being made out of Burly or Gnarly spec steel, but keeps the Fatty name.
The way to see what the pipe design does to the power, other than riding it, is for someone who knows 2 stroke pipe construction to look at them side-by-side and measure different parts of the pipe to see the differences and then state the theoretical difference they make. So many other factors effect HP and power delivery it is hard to say just how the bike will react to the pipe change, other than when you dump a stock two-wall like on the KDX or RMX and go to a real expansion chamber.