My FM70 Mod
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Joined: Mar 2007
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From: Pa
My FM70 Mod
I like my FM70 muffler I have but I want just a tad more sound out of it. I was going to buy a Magnaflow muffler but I figured I would try to modify my FM70 first to save some $$$ and if I screwed it up I would just buy a new muffler.
What I did was block off the one chamber directly inline with the inlet (Small Hole) in the picture below.
I took a piece of 10 Ga. Steel Sheetmetal and cut out a 1 3/4" circle to fit inside of the hole to block off the chamber. I used some weld through primer on the back of the disk I cut and MIG welded the disc to the opening blocking off the chamber. I welded the disc flush with the top of the chamber opening. After I finished welding I sprayed some high temp paint over it to prevent rusting and I was done.
Overrall I'm happy with the result. The muffler has more bark to it but not overly much. I have about 800 miles on it so far and I have not noticed any drone at any rpm range. I'll eventually get a video clip and post it.
What I did was block off the one chamber directly inline with the inlet (Small Hole) in the picture below.
I took a piece of 10 Ga. Steel Sheetmetal and cut out a 1 3/4" circle to fit inside of the hole to block off the chamber. I used some weld through primer on the back of the disk I cut and MIG welded the disc to the opening blocking off the chamber. I welded the disc flush with the top of the chamber opening. After I finished welding I sprayed some high temp paint over it to prevent rusting and I was done.
Overrall I'm happy with the result. The muffler has more bark to it but not overly much. I have about 800 miles on it so far and I have not noticed any drone at any rpm range. I'll eventually get a video clip and post it.
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Rep points for that one 
Ingenious! I wonder though, what it does to the flow of the muffer? Not much, I'm gathering, given that chamber right in-line with the inlet seems to have a dead-end right after it anyway...
Ingenious! I wonder though, what it does to the flow of the muffer? Not much, I'm gathering, given that chamber right in-line with the inlet seems to have a dead-end right after it anyway...
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From: Pa
I don't think it hurt the flow of the muffler anymore than when the exhaust was allowed to go into the chamber, but who knows.
The main reason I pulled the exhaust was to replace the section of pipe between the cat and muffler. I had a local exhaust put my cat-back system on because I didn't feel like dealing with it and a pipe had to be custom bent. The shop didn't have a Mandrel bender so as you may have guessed the tube was collapsed down to about 2.3" at the 2 bends on the pipe. Those bad bends are not good and drove me nuts. While I had the exhaust apart I figured I modify the muffler as well. Below are some pics of the old pipe and the new pipe I fabbed up out of two 3" 45 degree magnaflow stainless mandrel bends. Since doing the work I've noticed the top end power to be better.
Cut away pic of the old pipe from the muffler shop
Pics of the new pipe I fabbed up.
The main reason I pulled the exhaust was to replace the section of pipe between the cat and muffler. I had a local exhaust put my cat-back system on because I didn't feel like dealing with it and a pipe had to be custom bent. The shop didn't have a Mandrel bender so as you may have guessed the tube was collapsed down to about 2.3" at the 2 bends on the pipe. Those bad bends are not good and drove me nuts. While I had the exhaust apart I figured I modify the muffler as well. Below are some pics of the old pipe and the new pipe I fabbed up out of two 3" 45 degree magnaflow stainless mandrel bends. Since doing the work I've noticed the top end power to be better.
Cut away pic of the old pipe from the muffler shop
Pics of the new pipe I fabbed up.
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From: Pa
Could you possibly post my video when I get everything figured out?
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Joined: Mar 2007
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From: Pa
Yeah the pipe changed a purplish/red color, it was shiny stainless. The pic was taken after about 500 miles on it.
I got a sound clip but I'm having problems uploading it through Photobucket.
I got a sound clip but I'm having problems uploading it through Photobucket.
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From: Pa
Finally got my video uploaded. The camera was a little close.(6'-7' away) For those who don't know truck has Throley headers/ypipe, 3" Dynatech cat, FM Force 2 Cat-back w/FM70 with above mod and a 4" x 12" tip.
Video of 6.8l Exhaust - Photobucket - Video and Image Hosting
Video of 6.8l Exhaust - Photobucket - Video and Image Hosting
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Finally got my video uploaded. The camera was a little close.(6'-7' away) For those who don't know truck has Throley headers/ypipe, 3" Dynatech cat, FM Force 2 Cat-back w/FM70 with above mod and a 4" x 12" tip.
Video of 6.8l Exhaust - Photobucket - Video and Image Hosting
Video of 6.8l Exhaust - Photobucket - Video and Image Hosting