I have an '00 cr250 and while trying to get more lowend it was suggested I try the Fatty over the Gnarly. Some say the gnarly makes it harder to jet cleanly over the entire range and most of the jetting became a compromise. Some blubberiness somewhere in the power range. I have yet to install the Fatty and try but it's going on for this weekend.
I put the Gnarly on my 00 CR250 and it really made a BIG diiference in the bottom to mid acceleration. So much so that for really mudfest races I'm going to run the stock pipe. Keep in mind that I ride Enduro and H/S but power is power and that pipe makes it. By the way, I didn't have to change any jetting specs and it runs super clean from bottom to top.
Do you run a SA with it? If so, which one? What other mods have you done to the bike.....I'm trying to get some lowend in the thing for enduro work and although I've gotten some, not as much as I'd like.
WR, the Gnarly is the same design as the Fatty, just with heavier guage steel.
derekb_55, Try extra spacers in the exhaust (the metal o-rings between cylinder and pipe) You can run 3-4. They seem to help some, effectively lengthening pipe length. I have also heard good things about power valve cover spacer (or larger volume cover), although haven't tried them personally. But best bang for your buck will be a port job specific to low end power. Spend you pipe money on the porting, you won't regret it. I have used the Gnarly pipe and PC pipe, neither was as good as stock IMHO.
I suspected the pipes to be the same but my dealer told me to try the FATTY. I have the pipe washers(3) and a pv cover spacer with the torque reeds and flywheel weight also and the bike is ok. I haven't tried it yet with the fatty. Porting is probably the next step.
Where are you getting this info. that the Fatty and Gnarly are the same with just thicker material? :silly:
Now granted, I didn't test on a CR250. But, on my YZ250 I have tested the FMF Fatty, Gnarly and SST pipes, along with the PC unit. I conjuction with this I also tested the FMF Power core II, Shorty, stock, PC standard and shortened silencers with these pipes.
After testing all these pipes and silencers in different combos, I can tell you each one is much different than the other. I even ran three of the different length silencers back to back on the dyno with the same pipe. The silencers probable make as much or more difference in power as the pipes.
I have rode CR250's with both Fatty and Gnarly pipes, not back to back as with the YZ, but they are different.
As gawoodsrider suggested, I think the Gnarly makes too much bottom end. You put the Gnarly and Shorty together and you have more bottom than you can imagine.
If you're talking '01 yz250 then it's tough to compare the bottom end to the cr250's. I've ridden them back to back and the yz is better than the cr down there. Now I've tried a cr with the Gnarly and it's good but it still wasn't a match for the stock yz. I have yet to try the fatty on my cr but I still think I have to get it ported.
When looking for bottom end, Rev vs. Torque is the issue rather than Gnarly vs. Fatty. I have a Gnarly Rev and a Fatty Rev for my KDX. Both pipes are the same (power, jetting, etc.) except for pipe wall thickness. FMF also offers the Gnarly Torque for KDX. Other bikes, like Gas Gas, have only a Gnarly (not Rev or Torque) pipe. It sounds like on some bikes, the Fatty is a Rev, and the Gnarly is a Torque.