Hey,,,my xr600r has 13 discs in the supertrapp and a few people have been

bitching about the noise...no cops yet??,,,,If I take it down to 4 or 5 discs

I've heard this will lower the noise????

My real question is if I do the change,,,,will this effect my "rich/lean" mixture???

thanks Newbie :ride:

i've got 18 discs in my trapp. i dropped down to 6 to see how quiet it would be and within 15 minutes put them all back in. it did make it a little quieter but cut my power by a 1/3. can't help with the rich/lean ? btw my pig is much quieter than 98% of the Harleys i hear.

the Supertrapp Race exhausts will never qualify as a "quite" exhaust :smirk:

i run 15 for topend riding and 10 for tractoring around the woods :thumbsup:

as u remove disks u r reducing flow/adding back pressure(better for bottom end/torque)...this richens the mixture

on the other had adding disks increases flow/reduces back pressure(better top end/peak HP)...this leans out the mixture

personally on these bikes i wud never run less than 7 disks.

the only time jetting is critical is if ur running on the lean side and adding a significant number of disks, leaning it out further :thumbsup:

also sound wise if u control ur right hand and stay off of WOT u can keep the sound down :smirk:


:cheers:

I was running 16 discs up until last weekend. I went out and bought new packing and dropped it down to 10 discs which includes the heat deflector. Didn't make too much difference on power but quieted her down quite a bit.

By the way I called Supertrapp to ask them about the discs. The gal I talked to was probably over 50 and I was thinking this would go nowhere fast and that lady taught me more about that exhaust then I could have expected. She said on a 650 XR you do not want to go lower then 8-10.

Hey guys, it's important what size SuperTrapp discs your using. 3" don't use the same amount as 4" or oval discs. Displacement cam and carb are relevant too. The general rule I have used is outlet area a minimum of %60 of inlet pipe area. Going less than that will reduce power drastically while only slightly reducing noise level. The 2-3" discs per 100cc rule works too for getting in the ballpark. That's a baseline too start at. 4" discs don't need as many and oval discs even less. A better option for less noise is the deflectors available for some disc sizes. First and last disc in a stack have virtually no flow so don't count them in your calculations. The big problem for the disc design is they disperse the noise in all directions. If you redirect as much to the rear as possible percieved noise level is reduced. I have 14 large oval discs on my 650 because of the cam/carb/pipe combo. Its not much louder than it was with 10 before the hopup.

valvesrule said:

u bring up sum gud points...

my comments were in reference to the 4" SuperTrapp Race exhaust...

...as us stated and i have observed the outter ends of the disk stack do not flow exhaust gasses but i did include them in my disk count :thumbsup:

i know sum people have them and like them but IMO stay away from the 3" ISD2 Series(quite or race) for these big bores :smirk:


:cheers:

P.S. so on the "oval" does it approximately measure ~4" in one dimention and ~3" in the other???

I base the 2 per cc rule on 3" cause they were the first available in the 70s and the ones I learned on. I like them because they work better than any Krizman type spark arrestor of the day and they are quieter than all current screen types I have used. Take a feeler gauge and check the gap (average) between assembled discs, do the math if you want to do the area rule. Use inside diameter of the disc to calculate. I can't tell you the exact numbers cause I kinda "freeball" it anymore. If jetting is anywhere close to right when you start it won't change much while swapping discs. Don't worry about rejetting til you find the best noise/power ratio. 3" internal discs forget all this and put as many discs as the screws will hold and run it. The case itself is the restrictive part. I have a hi comp 617cc motor running great with one(18 discs). I can't tell you just what the oval discs measure i.d. mine are all installed. And the FMF Megamax discs are a different size too. Thinking both are more like 4 1/2 X 3 1/2. When you get your base count going 2 disc less will be the least # discs you should try. Less will get your power. As many as 6 more might be needed for best power. More than that and you might as well have open exhaust both power and noise wise. Good luck!

thanks to all you guys!!!!!!!!!!

XR-Cyclone said:

A lot of good info in this thread. Thought I would clarify that my supertrapp is the 4" cacn type.:banana:

I too got concerned about noise and reduced my disc count from 12 to 7. I lost quite a bit of top end power. I travel up a 7% grade 10 miles long every night on my normal commute so each night is like a dyno test. I slowly added more until I got back to 12 again, 4" discs. More than 12 made no difference so I settled there.

I still felt guilty about noise till one time a Hardley passed me on the hill, I could not even hear my bike at all. I have no more guilt now. Though I do practice the tight hand volume control if needed as Kenzo suggests.

Thank you for not asking how I let a Harley pass me.