YZ125 Pipe Comparison

Figured I'd throw out what I've tested thus far...
 

SST was marginally better than stock but not by much.
PC was a big disappointment - but more on that in a second.
FMF fatty a clear winner here...I didn't take the time to equalize EGTs for each pipe - which may make the results if each set up were optimized with best jetting for each pipe a little different but in any case good general picture painted

 

I tested a PC off a 2003 model yz and it matched the FMF through the curve almost exactly, so where did PC go wrong? One of the "selling" notes when yamaha released the 125 in 2005 was a straightened exhaust header - and in my experience - if a header can be kept straight for at least 5-6 inches you are good - if not you typically hurt power.  On the 2003 PC pipe - it has a straight header - on the new style pipe - it makes  turn almost immediately.  Not good!

 

The 2003 model pipe wont fit the chassis correctly but could cut and welded to fit better with some effort if you are a must have PC fan.  PC may have updated their pipe from what I have - not certain.

 

Screenshot (21).png

Edited by harrperf

Thanks for your hard data !  Me personally am "anti-pipe" and feel that for the average rider pipes are wallet bait. Unless you have an expert level tuning and "seat of the pants " feel your wasting your time.  However , among the expert ranks where 1 hp can be the difference between a poduim win (or not) a pipe can potentially offer REAL gains by means of reduced lap times.

I've experimented my '08 YZ144  with stock and the FMF fatty, and like your finding do feel a slightly better mid to upper pull. Many of us here are in agreement, that the OEM YZ pipes perform excellent and again getting real gains from an aftermarket pipe can be a challenge.  The performance shop that ported my 144 cylinder also commented that the 144's do respond well to the FMF Fatty . I'm an old vet, and for me it's all about attempting to extrude broad usable power , and efficiently putting that power into the dirt to fend off those pesky easy to ride 4 strokes !  ;)

Edited by Polar_Bus

Thanks for your hard data !  Me personally am "anti-pipe" and feel that for the average rider pipes are wallet bait. Unless you have an expert level tuning and "seat of the pants " feel your wasting your time.  However , among the expert ranks where 1 hp can be the difference between a poduim win (or not) a pipe can potentially offer REAL gains by means of reduced lap times.

I've experimented my '08 YZ144  with stock and the FMF fatty, and like your finding do feel a slightly better mid to upper pull. Many of us here are in agreement, that the OEM YZ pipes perform excellent and again getting real gains from an aftermarket pipe can be a challenge.  The performance shop that ported my 144 cylinder also commented that the 144's do respond well to the FMF Fatty . I'm an old vet, and for me it's all about attempting to extrude broad usable power , and efficiently putting that power into the dirt to fend off those pesky easy to ride 4 strokes !  ;)

 

 

 

 

I think in this instance it's fairly clear cut - the fatty is one of the cheapest gains you would get per dollar.

 

I like the character of the stock pipe on the track quite a bit and depending upon the cylinder's porting arrangement all the pipe data changes.  If modified to fit a certain pipe - then of course running that pipe is a must.  If modified where it fits "no pipe" of course a custom pipe is a must.  Fitting the pipe and cylinder arrangement to one another is the single most important aspect IMHO of a good build.

 

Figured I'd throw out what I've tested thus far...

SST was marginally better than stock but not by much.

PC was a big disappointment - but more on that in a second.

FMF fatty a clear winner here...I didn't take the time to equalize EGTs for each pipe - which may make the results if each set up were optimized with best jetting for each pipe a little different but in any case good general picture painted

I tested a PC off a 2003 model yz and it matched the FMF through the curve almost exactly, so where did PC go wrong? One of the "selling" notes when yamaha released the 125 in 2005 was a straightened exhaust header - and in my experience - if a header can be kept straight for at least 5-6 inches you are good - if not you typically hurt power. On the 2003 PC pipe - it has a straight header - on the new style pipe - it makes turn almost immediately. Not good!

The 2003 model pipe wont fit the chassis correctly but could cut and welded to fit better with some effort if you are a must have PC fan. PC may have updated their pipe from what I have - not certain.

Thanks for posting hard data! What length silencer did you use with the fmf fatty pipe? Thanks in advance.

i knew that the pc pipe for the 05 + had that hook design i have to maybe dig up the dirt rider from 05 where they tested a pc modded 125 it mentions this in the article and why they made it that way. backs up what an older user on here told me back then that the fmf fatty was good pc bad design. still want to know what the dep is really like the hgs and the dr d pipe. the scalvini sounds like a pretty pipe that doesn't do much. never checked i wonder if messico makes one now.

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