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Understanding Yoshimura's RS-4 inserts

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Yoshimura has several inserts for their RS-4 exhaust system that are not so easy to figure out on paper or after a tech call to Yosh.

My 2012 CRf450 ran good with the FMF RCT 4.1 exhaust that replaced the tiny outlet of the stock exhaust.  The outlet of the FMF muffler was about 1.67".. much bigger than the 1.05" stock outlet.

 

I then tried a full titanium and carbon fiber Yoshimura system which comes with their "AMA Sound Insert" which is 94 db.  I was surprised by the tiny outlet the Yosh muffler came with. It measured only 1.24" in diameter!

 

I had a very confusing call with Yosh tech. i dont like loud but I asked them which insert would give the best power.  He suggested the 2M Max insert. I asked him how many dB it was rated at and he said 110 dB. I naturally figured that the diameter of the opening of the 110 dB insert must be bigger than the 96 and 99 dB inserts so I asked him the diameter of the inserts and said they are all 1.5" which is written on the packing label. This made no f'in sense whatsoever so i ended the call and ordered every insert they sold to figure it out myself as there is no explanation anywhere about their insert system and it is not intuitive.

 

None of the inserts are 1.5" in diameter.. they are all less than that and all much smaller then the FMF. 1.5" must be the size of the muffler opening and not the nsert so refering to it is totally useless. The 99 dB insert measured 1.42" in diameter.. still no where near the size of the FMF outlet. If the 2M max insert is rated at 110 dB, I expected it to be bigger in diameter.. nope, it was the exact same 1.42" in diameter as the 99 dB insert except it had a piece of perforated steel welded over the end of it which makes it at least a but more restrictive than the 99 dB insert so how the heck could it be rated at 110 dB. The only answer to that is that the 2M max insert is rated in a different way than all the other inserts they sell and actually would be quieter than the 99 dB insert if measured the same way. You would never figure this out from the info they provide.

 

End of story.. if you want the least restrictive insert, go with the 99 dB insert which is what I did and dont bother asking Yosh or looking for an explantion in their literature as you won't find it.

 

Stock 2012 CRF450 - 1.05"
Yosh "AMA Sound" insert - 1.24" (94 dB)
Yosh "2M Max" insert - 1.42" + perforated screen on the end (I am guessing around 96 dB)
Yosh "99 dB" Insert - 1.42" (99 dB)
FMF RCT 4.1 - 1.67" (the loudest of all but from the rider's seat not that much noticable over the Yosh 99 dB insert)

 

The Yosh with the AMA sound or 99 dB inserts will defintely gave the bike more lower end power than the FMFbut not as much on top and not as smooth a transition from bottom to mid. The Yosh full carbon fiber and titanium muffler looks great ,but beware, it is pig heavy for the materials used.. it is .84 lbs heavier than the FMFaluminum and steel muffler and 1.58 lbs heavier than the FMF titanium RCT muffler!

 

Anyone running without the insert at all? This would bring the Yosh outlet diameter closer in size to the FMF RCT 4.1 muffler.

 

mike

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I see the points you are making, but remember bigger size doesn't not mean bigger gains. Basic fluid mechanics

Yup got that and it also depends where in the powerband you are looking for the gains. My experience so far with the bike is she runs better overall the more I uncork it.

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Similar story.  Picked up a used Ti/Ti RS4 system off CL for a 10 last year since it got the best reviews in the mx mags..  Went on Yosh's website & also seen different inserts available & wanted to understand how they affected performance.   Also called them up & talked to one their techs that really didn't provide any good info & didn't seem to have a grasp on the different inserts.   Ended up with the 99db one & the 10 motor now feels stronger in the entire rpm range than 05 / 06  models owned with stock motors.    Don't have any experience with the FMF system , but the motor pulls strong on top after an Eddie S. remap.  

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