FMF Fatty vs. SST

[MX-727]

I just tried the FMF Fatty, back to back against the SST.  I actually rode with the Factory Fatty, but I find it hard to believe that the difference between the two Fatties would be much.  I used the shorty with both pipes.  The bike was my 2002 YZ250 with a milled head from Eric/Forward Motion, V-Force reed block/reeds and VP C-12/Yamalube 2R at 32:1 

I warmed up and rode with the SST, which I've been using for the last year, at a tighter track with several jumps right out of corners.  After getting a good feel for the track and bike, I switched the pipes.  I could immediately feel a huge difference in power delivery.  I was surprised because I didn't really expect there to be much of a difference.

The SST feels strong and has quite a bit of overrev when compared to the Fatty.  The Fatty pulls much harder off the bottom and into the midrange, but it signs off a lot earlier.  The differences were evident in the gear selections I used on the track.  With the SST, I rode almost the entire track in second with the occasional shifts to third on the faster sections.  The Fatty required/allowed me to ride in third and  fourth in the same situations.  Some of the slower corners were still easier in second, but an immediate upshift to third was called for.  Most SST second gear jumps required third with the Fatty.

I had debated whether there was any reason to even consider the Fatty, but after riding it, I found that the two pipes really seem to compliment one another.  I'll use the SST for faster, more open tracks such as Cooperland.  The Fatty will be used on the tighter SX style tracks. 

Understandably not everyone wants to buy two pipes, so if you are a revver, you'll like the SST and if you like to short shift, you'll like the Fatty. 

 

[rickyd]

Hey thanks for the review, i too have a FATTY & a SST for my KX.. Haven't been able too use the SST since i didnt buy a sparky for it, need too go out too a privately run mx track..
Thanks again,
RIck
PS.. Is the Factory Fatty supposed too be better than the regular FATTY?? Or is just the finish??

 

[bclapham]

interesting....ive got erics low end porting on mine (01) with the SST/shorty. i thought they would clash, but they compliment real well. it revs out real good but will pull 3rd through any corner! milling the head for race gas realled stopped it from revving, i put a thicker base gasket on and finally got the fmf ignition on there also, now it pulls very strong from the bottom but really revs, its the best ive ever had it running

its quite odd since i was considering the fatty for my new rm144 project since i was under the impression it would help the wider bored engine to rev out also.

 

[MX-727]

There were some comments made by a few of the magazines that the Factory Fatty performed "better" because it is made of thinner metal. People I trust to understand these things (DRNers or course) don't think very much of that theory.

It may not be that the Fatty kills overrev, as there is still a lot there, it's just in comparison the SST provides a lot more.

 

[MX-727]

Alright, I put some more time on the Fatty and I still love it for tighter tracks. Now that I've become used to it, I realize the bike still has a ton of overrev, just not as much as the with the SST.

As an all around pipe, the Fatty may be the best choice for most people.

 

[Matt_H]

When you say fatty is it the original or the factory?

 

[MX-727]

Factory

 

[bclapham]

Hey MX- just wanted to bump this to the top. did you use the 1st or 2nd gneration shorty silencer?? the new ones have kind of a reducer washer welded into the end of the stinger part- i think it is supposed to help top end and overrev. i am debating toretrofit one to my silencer. i currently run the SST but i am trying the Fatty soon- i like the idea of running 3rd a bit more often. which do you prefer nowdays????

 

[Binky]

Well, now that you've got yourself all convinced about the performance
quality's of each pipe, let me tell you what the dyno says.....All compared to stock.
YZ250...williams motorsports dyno, Nov 2003.
Fatty....slightly more LE, Loss on top of 4%
Factory Fatty, Same as Fatty on bottom, slightly higher RPM and HP peak than stock, untrackable on printer graph.
DOMA...Worse than Stock everywhere.
SST....Less bottom, Same midrange, 2% more peak HP
DEP....only pipe tested that was better thruout power band.
PC Pipe..not tested.
Oh yeah...throw the vforce away. Unless you like giving up 1.5hp on top.
Let me know if you want the charts.

 

[bclapham]

yes please, email them to me at bclapham@scripps.edu

ive had v-force on 2 bikes now, nothing but jetting troubles and they went back on ebay!!! i am going to try carbon reeds on the yz next time.

 

[Chili]

Binky any SST dynos on a 03 RM 125 with an SST setup? We picked one up for a song for my son's bike but I don't know that I want to use it if it gives away bottom end since that will most likely be where he needs help after just moving up to the 125's.

 

[bclapham]

Chilli: just give it a try and see how it runs. if you are worried about bottom end, just fit a billet clutch basket and tell him to give it some clutch!:)

 

[Chili]

Bruce I've been trying to turn this kid into a clutch abuser for 2 years now, someday we'll get it right :laugh:

 

[Binky]

No runs on the RM125, sorry.
We have done 01,02,03 - KX250.
the 02,03 - KX125
The 02-04 - KX85
and the 02-04 -YZ250
and the 04 KX250f

 

[bclapham]

Binky- please email me the kx125 and the yz250 runs

thanks:)

bclapham@scripps.edu

 

[Binky]

Binky- please email me the kx125 and the yz250 runs

thanks:)

bclapham@scripps.edu

Will do...gimme a day or two.

 

[bclapham]

:thumb:

 

[marcusgunby]

Is this any use?? its a 02 rm125 std vs a SST pipe-not very good the sst-the 03 might be different but i doubt it will change much as the 02 was very similar i think.

 

[Chili]

Thanks Marcus. Not sure of the differences to be honest but I do know that the 02 and 03 pipes are different part numbers so I imagine there is some differences. But most likely the way the pipe produces power is probably pretty consistent year to year. It's of no huge concern as I don't imagine we are going to be in a rush to get more power out of this bike his first season on the 125's. More likely will be looking to move the power around and perhaps enhance the bottom end. I bought the SST because it was a steal of a deal and I always like to have an backup pipe and silencer around during race season.

 

[Studboy]

Well, now that you've got yourself all convinced about the performance
quality's of each pipe, let me tell you what the dyno says.....All compared to stock.
YZ250...williams motorsports dyno, Nov 2003.
Fatty....slightly more LE, Loss on top of 4%
Factory Fatty, Same as Fatty on bottom, slightly higher RPM and HP peak than stock, untrackable on printer graph.
DOMA...Worse than Stock everywhere.
SST....Less bottom, Same midrange, 2% more peak HP
DEP....only pipe tested that was better thruout power band.
PC Pipe..not tested.
Oh yeah...throw the vforce away. Unless you like giving up 1.5hp on top.
Let me know if you want the charts.

:ohmy:

Here is my experience with the doma pipe/silencer.
Bike: 02 YZ250, V-Force 2 High tension, Stock ports, Stock compression. 4,000 FT Alt. Pump/C12 Mix 32:1 MX2T.
I'm not sure what the dyno says, but here is what I can say back to back with the stock pipe/silencer combo. Jetting adjusted of course.

The stock pipe has a very wide range of power with very little hit. The bike is very rideable with this pipe with a wide and smooth powerband. I prefer this pipe for off-road and slippery/technical conditions.

The Doma pipe feels like the motor revs easier. The power down low feels less, with a bigger hit and a definate overrev advantage. The bike feels much stronger mid to top. The bike also climbs sand mountain much faster with the Doma on instead of the stocker.

If the doma makes less power everywhere on the dyno, how come the bike climbs sand hills much faster? Altitude, or what? :think:

 

[Binky]

:ohmy:

Here is my experience with the doma pipe/silencer.
Bike: 02 YZ250, V-Force 2 High tension, Stock ports, Stock compression. 4,000 FT Alt. Pump/C12 Mix 32:1 MX2T.
I'm not sure what the dyno says, but here is what I can say back to back with the stock pipe/silencer combo. Jetting adjusted of course.

The stock pipe has a very wide range of power with very little hit. The bike is very rideable with this pipe with a wide and smooth powerband. I prefer this pipe for off-road and slippery/technical conditions.

The Doma pipe feels like the motor revs easier. The power down low feels less, with a bigger hit and a definate overrev advantage. The bike feels much stronger mid to top. The bike also climbs sand mountain much faster with the Doma on instead of the stocker.

If the doma makes less power everywhere on the dyno, how come the bike climbs sand hills much faster? Altitude, or what? :think:

I'm not gonna argue with you...I just know what the
dyno say's and what it does not say.
Your doma is crap. However it feels to you.

 

[Studboy]

I wasn't saying that your dyno is crap either... Maybe altitude, maybe the V-Force, maybe the load makes the difference, but for sure the doma is faster on my bike in the sand.

 

[jho410]

Does anybody have an opinion on the FMF Gnarly?

 

[marcusgunby]

The Gnarly is a true low end pipe that is designed to favour bottom at a trade for top-it should give more bottom as it is a no compromise design for bottom end power.If you dont use/need the top or overrev of the std pipe then it should work well.

 

[marcusgunby]

Studboy when you say you know it is faster? how are you measuring this? timed runs back to back maybe a good indicator of performance-seat of the pants isnt really as it's maybe a hit that makes it feel fast.This generally provides a fast feel, but slow lap times and un even traction.The dyno isnt perfect but it is repeatable and can be accurate when used correctly-this isnt the same as seat of the pants riding which is determined by many factors.