has anyone done this?

do you get a gain in horsepower, if you rejet accordingly?

what are the pros and cons of this?

thanks

 

Look at the new 4 wheel atv action(april) I tried it before we got a bunch of snow in Nova Scotia, and It is a lot louder. It might have a tad more power, but I would leave it in. although I like the sound of a somewhat loud exhaust, lots of people find it distracting, and more trails may close down. Just keep it in, like everyone else says.

 

Here's my opinion... A while ago I had a friend with welding skills remove the restrictor from the end cap, but to keep it legal for where I ride had him re-attach the spark arrestor screen. While it was a little bit louder with the modified end cap (definitely much quieter than most aftermarket silencers though) I don't think it made much of a difference at all. Just from a "seat of the pants" kind of observation, I think it may have added a tiny bit of power on the top end, and probably lost a little on the bottom end.

The bottom line is the stock silencer itself is somewhat restrictive, and modifying the end cap isn't going to make a noticeable difference. From some of the other discussions about the stock silencer though, some are saying if you drill another hole next to the existing one...looking in from the end of the silencer...this helps improve the outflow of exhuast. I've already drilled an extra hole in my stock pipe, and with my modified end cap will hopefully get a chance to test it out this weekend to see if it makes any difference. If it does, then I'll be selling my "way too loud" FMF Powercore IV2 SA pipe.

 

This is what I did to mine. Took the end cap off, ground the spot welds from the screen, cut just behined the welds(removing the center),poot the screen back on and welded it (you can weld stainless steel with mild steel rod)and just for a little extra spark eresting I rapped a pece of OO steel wool around it and stoffed it back in. I don,t know about preformance but it just sounds better. Good luck, hope all comes out well.


Danimal
2000 400EX

 

Read an article in one of the major mags called hidden free horse power they did a crap load of dyno runs on the 400ex and completely stock was 26.3 hp and exhaust baffle out was 27.0 hp I wouldnt say that .7 hp is a significant gain

 

Well what you have to do is unbolt spark arrestor(3bolts) from back of
muffler. You will notice spark arrestor screen is held on by ring at
base with 3 weld points. Carefully grind down welds until you can get
ring off. Dont grind to much into main housing.Once ring is off gently
pry loose screen,some of it will be damaged but as long as ring covers
it up the spark arrestor will still work properly. Now that the screen
is off you can cut the housing to the quiet core insert(skinny tube
with all the holes). Cut appx 1/4 above weld on main housing of spark
arrestor,draw circle around tube so cut is even.. You can use hacksaw or
cutoff wheel. Metal is appx 1/16 inch thick on housing.Once wall is cut
you can slide quiet core out with 1/4inch of housing skirt on it.File or
sandpaper edges of housing where cut so it is fairly smooth.Reinstall
screen and ring.You can braze it or JB weld it back on just make sure
there are no breaks in screen past collar.We wouldnt want to burn down
our fav riding spots.Put some anti-seize(very important) on 3bolts and
put sparky back on muffler.If you ride below 3k feet these are jets you
need. 40 pilot,160main,move needle clip down one notch(from center#3
from top to #4 from top),air screw out 2.5 turns from bottom. 3K-5k 40
pilot,needle clip down one notch,155-158 main. 5k and up stock pilot,
needle clip one down,152 main. Install K&N filter(ha 4099) with
prefilter(ha4099ow)(very important),put 3 inch hole in airbox lid
towards back center where it curves in.Put in splitfire
plug(sf416c).dont forget to adjust valves after first 10hrs.(.005
exh,.004Int)and again every 100hrs.This will give you 5+hp. I picked up
6.2hp on my quad at sea level.Obviously higher elevations with leaner
jetting will get lower results.the great thing is it only costs about
$50 in parts(filter/ow,jets,plug)if you really want to see it scream put
on White bros rev box,$110.ENJOY!!!