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Exhaust? Yoshimura, FMF, Pro Circuit?

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Debating on finally biting the bullet and doing exhaust on my KX250F just don't know about dropping 800 bucks on such a fragile part. Does it make that big of difference for the bike? I know there are a lot of manufacturers now who is making the best product?

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i just got my 250 and read about the stock pipe making the best power , i did some research and found a dyno of just the yosh slip on and it made about half a hp more in one spot and lost alittle in a diff area , please correct me if im wrong but the stock setup has a resinator , for better bottom end , i dont think the yosh head pipe does? really I think unless your a pro sucking every last hp out of the thing , or your just going for bling , your not going to benefit ,personally I hate looking at that huge trash can hanging off the back of the bike.

sucks that nobody publishes dyno's anymore , I hate dropping anywhere from 200.00 to 1000.00 on an exhaust and not get to see a full dyno with hp and torque specs

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Even a dyno sheet is often suspect.

What kind of dyno? Some (the most common rolling drum) only accurately reflect peak power.

Any changes made to the bike between runs? Was the bike rejetted for the new pipe? Was it properly jetted for the old pipe?

Same bike (not just same model)?

Any changes in air desity between runs?

Tires?

Tire pressure?

Smoothing?

 

No manufacturer is going to publish a dyno sheet where they cannot claim at least a 5% increase in power. Buyers hear the increase in sound and are convinced the bike is 'way faster'. You never see people show changes in lap times, which often increase due to less usable power and sometime a more abrupt power delivery.

The only real gain I see from an aftermarket pipe on most bikes is the weight loss. Cutting back on Twinkies is cheaper.

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Even a dyno sheet is often suspect.

What kind of dyno? Some (the most common rolling drum) only accurately reflect peak power.

Any changes made to the bike between runs? Was the bike rejetted for the new pipe? Was it properly jetted for the old pipe?

Same bike (not just same model)?

Any changes in air desity between runs?

Tires?

Tire pressure?

Smoothing?

No manufacturer is going to publish a dyno sheet where they cannot claim at least a 5% increase in power. Buyers hear the increase in sound and are convinced the bike is 'way faster'. You never see people show changes in lap times, which often increase due to less usable power and sometime a more abrupt power delivery.

The only real gain I see from an aftermarket pipe on most bikes is the weight loss. Cutting back on Twinkies is cheaper.

thats what all the road bike guys always say "it's way cheaper to take weight off yourself than off the bike"

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Maybe I could wrap that trash can in carbon fiber tape and slap a Yosh sticker on it ,hehe , You make a great point about power delivery , on track lap times are where its at, example my son has a new KTM 125sx he's 120 pds we ran it stock a couple races , and he always complained it wouldn't hook up , i finally sent out the  suspension and had it dialed in for his weight , and now he loves it and lap times went down , I then decided to get the sxs ignition for it , I ran it up and down the street ,and new it was faster ,but when he got it on the track he said the power band wasn't as linier  and hit hard , and wasnt sure if he liked it , we just got our kx250 we immediatly found that the stock springs are not close for his weight, besides his favorite bars, the springs are the first mod this bikes getting

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Let me clarify.  C4MX builds our motors.  I trust Frenchie completely.  We see the dyne sheets.  Yosh puts out a better top end power.  On a 250f that's where it matters for us.  

have you seen a dyno sheet  with the stock header ''that has'' resinator and the yosh slip on ? or is that extra hp on top comming from a header without 

the resinator , 

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In my opinion the extra hp comes from the genius putting it all together.  It's an off the shelf, no mods, yosh full system.  The motor is significantly better than the customer spec PC one we used las year.  

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ok ,cool , is your builder also working with the mapping , or in other words will the system work well with the stock mapping?

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I agree, spend the money on suspension, tyres, and rebuilds, not worth it to go aftermarket unless you want bling.

 

Nothing like a stock bike beating a blinged up bike.       

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i have been able to find yosh dyno runs full system and slip*on not real impresive , but they are not dated nor do they say what yr kx they were i think they are pre 2012 sheets ,i would like to see a new run on the 13 14 15 bikes, but I do agree anyone serious about racing suspension is first , i'll be the first to admit i'll take a slower properly suspended bike , then a rocket motor and a poorly suspended bike, but its never a nice feeling working your ass off ,in corners and jumps , and see that hp pull back up on you in a long strait, also hp matters when your wanting to get up in the front off the gate and thats a fact

Ive also found full yosh systems for under 500.00 bucks, a simple remap for 100.00 might be a better choice hp per dollar

Edited by fgrote

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ok ,cool , is your builder also working with the mapping , or in other words will the system work well with the stock mapping?

We are running a Vortex ignition on the mod bike (a couple in air GET failures were enough).  The bikes are either bone stock or mod.  If they are mod, everything is changed.  There are enough people out there that dyno various pipes (who aren't beholden to a company) you should be able to get the info you seek.  Dyno is only part of the battle, but you want solid numbers.  Then you get to the feel part, which can be massaged with ignitions.  Once you get the hp numbers you want, feel is critical, at least for our pilot.  The stock KX ignition is too limited in its remap parameters.  

 

We just started running the Yosh based on Frenchie's research.  Haven't put one on a stock bike.  We have a few PC pipes and did put one on a stock bike.   On a stock 250f they do seem to move the power around (up) which is nice.  But I don't know if they produce more power.  Of course, any aftermarket pipe sounds much better than stock and your neighbors will thank you.  

 

I agree on running a stock bike.  We run our stock practice bikes in most events outside a few large races.   But you know you are giving up between 7-9 hp on a built 250f running good oxygenated fuel, and in a short four lap race what you lose on the start can be enough to change the outcome.  Certainly the straights won't be your friend, so it's up to the corners.  We'll be running a stock practice bike this weekend at Mill Creek.  I think it's great practice to be underpowered (my rider disagrees), except at the big events.  

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great info, so here is what im after in the end , since my rider is only 125pds , adding hp will add unwanted  wheel spin with my situation , I just shot off an email to tokyo mods , to ask if its possable to see any noticeable gains just on the top  and leave the rest of the map alone ,one last thing whats your take on the extended dog bone , at our practice track , another seasoned rider said that part alone makes a huge difference , since pc publishes stock length and the new pc length which is only a 1.5mm diff , i was thinking of throwing our stock link on the mill and removing that 1.5mm , theres plenty of meat back there to take it out without compromising it 

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We run a ride engineering extended length dog bone on each bike.  Matt Borgic from JM Racing Illinois handles that stuff.  I wouldn't let a worry about wheelspin affect anything as I don't think you can account for that variable in isolation.  Four stroke have built in throttle control.  On a 250f I'd getall the power I could.  We just have a chronic over revver.  We are working on it, but still rev too much, so we put a lot of the power up there and extend the rev limiter.  Every rider is different.    Your machine skills may be superb but I wouldn't modify a suspension part like you discussed for MX.  It's never worth the risk.  They subject these bikes to too extreme of loads.  Don't overlook Frenchie at C4MX.  He's always responded quickly and his work is phenomenal.   And...  he'll recommend a Yosh.  Good luck to you.  You can email me at michael499@me.com directly with questions.  I don't know much beyond what I learn from the builders, mechanics and our maintenance program (4 practice bikes in circulation with 3 hours a day being put on one, and three race bikes).  But I'll gladly share what I know in the chance it could save someone headaches or money.  

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We run a ride engineering extended length dog bone on each bike.  Matt Borgic from JM Racing Illinois handles that stuff.  I wouldn't let a worry about wheelspin affect anything as I don't think you can account for that variable in isolation.  Four stroke have built in throttle control.  On a 250f I'd getall the power I could.  We just have a chronic over revver.  We are working on it, but still rev too much, so we put a lot of the power up there and extend the rev limiter.  Every rider is different.    Your machine skills may be superb but I wouldn't modify a suspension part like you discussed for MX.  It's never worth the risk.  They subject these bikes to too extreme of loads.  Don't overlook Frenchie at C4MX.  He's always responded quickly and his work is phenomenal.   And...  he'll recommend a Yosh.  Good luck to you.  You can email me at michael499@me.com directly with questions.  I don't know much beyond what I learn from the builders, mechanics and our maintenance program (4 practice bikes in circulation with 3 hours a day being put on one, and three race bikes).  But I'll gladly share what I know in the chance it could save someone headaches or money.  

thanks for your input,very helpful , I realize alot of builders won't be completly open about alot of things ,because of the R&D time put into testing , unless you have your checkbook out LOL

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Let me clarify. C4MX builds our motors. I trust Frenchie completely. We see the dyne sheets. Yosh puts out a better top end power. On a 250f that's where it matters for us.

Add the $2000+ price tag on top of the exhaust....You're referencing a top rider, we're talking an amateur at best, there is very little in common...

For a guy with a stock motor, I could put on a fresh knobby and play with sag and clickers and he would be $700 richer and a be quite a bit faster...

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Add the $2000+ price tag on top of the exhaust....You're referencing a top rider, we're talking an amateur at best, there is very little in common...

For a guy with a stock motor, I could put on a fresh knobby and play with sag and clickers and he would be $700 richer and a be quite a bit faster...

monk do you ever have anything positive to contribute , its always FRESH  knobby tires with you..... do you know either of us ? I know you know nothing about me, Ive been riding and wrenching on bikes for 40+yrs , I know you think 90% of everyone here  is cluless, it just gets old dude

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