Well I finally got the new exhaust on and I dynoed it.

Here goes the procedure.

Did some research and came to the conclusion that a Gibson catback would be an acceptabe performance system and it would be the quietest. I chose the swept side because it was recommended for towing and off roading.

I get the box from ups. The first thing I notice about the muffler is that it's not a muffler. This thing is a 3 inch pipe with little holes poked in it. It is covered by a larger pipe (outer shell of the muffler). In the middle of the "muffler" the smaller pipe has a 4" gap all the way around it and baffle walls between the little and big pipe. This thing is like a big silencer. Cool.

Intalling was a pain. My advice to people is to forget neatness and cut the old system off with a sazal. The pipe a foot after the cat, the two pipes just before the axle, and the hangers that hold the two pipes after the axle, they all had to be sawed because the were rusted to Hell and back. Once I got the old system off. I started the truck with just one foot pipe coming out of the cat. NICE. I went driving on the farm roads and damn did it sound nice. Still quiet, nothing like a harley or anything. But you could hear it roar when the engines revved and hear it burble when you downshifted. If I wanted a loud system I would probably just run a 3inch pipe after the cat with no muffler.

But I do want it to be quiet (and I spent all that money on a muffler) so I need to install the Gibson. This is straight forward and easy. Except for: This system comes in pieces. You have to fit the pipes together and then put clamps on. Well the last peice, the one that come out after the axle, kept rotating down. It would not hold even with the clamp. So I get a friend to hold it in place and I interlock two wrenches together. I then pull as hard as I can to tighten the clamp enough to hold the damn pipe. Snap. One of the wrenches breaks off and procedes to imbed the two pointy parts in my forehead. Well after 5 minutes off cussing I try to figure out what happened. The clamps are an u-bolt with a bar and two nuts. When I was torquing the nuts I managed to break the bolt. Upon inspection the bolt is made out of some sort of composite cement coated with chrome. So I went to O'Reilys and bought an iron one. Worked fine.

Now I have the system on. Quiet. Stock and idle. Resonace in the cab at 2000 RPM under power. Other wise you can't hear except with your windows down and then it's only slightly loader thaen stock. I notice the rear tires break lose more often then before when starting out.

I dyno at KC. See the graph below. Two runs. The first run (#8) was on the back tank which was nearly empty and with what i thought bad gas. On the second run (#9) I switched to the front tank full of good gas. Earlyier this year I dynoed before and got a baseline. #2 was the best it is just the truck with a K&N air filter. I will compare dyno run 2 with number 9.

You'll notice that the torque increased by about 4 ftlbs at lower RPM, peaked about 1ftlbs higher than before, and increased 14 ftlbs at 4400 RPM. It really helped after 3400 RPM. What this mean is that my HP curve doesn't fall as rapidly after 3800 RPM as it did before. I gained 11HP at 4400 RPM and 6HP at 4000 RPM. My peak it now 175HP and 267ftlbs of torque. But I have a flatter TQ and HP curves now. I now make 90% of TQ from 2000 to 3800RPM.

My next series of mods will be to free up intake some more. Hot rod says this is where the 351W falters.

The reasons I went with a single 3 inch pipe as opposed to two 2 inch pipes.
I have an exhaust area of 7.06 square inches.
2, 2 inch pipes have a total area of 6.28 square inches
I have a circumference (drag area next to the pipe) of 9.42 inches
2, 2 inch pipes have a circumference of 12.5 inches.
And, as I said before, this muffler has no restriction in it what so ever. Mandrel bent piping also.

All in all I'm happy with the system. Plus the 3.5 inch tip looks awesome.