I had a similar issue when my old shorty header cracked.... only it was a bad #1 misfire...

 

air travels faster across a rough surface than a smooth one sometimes...(hence the dimples in the surface of a golfball . the rough casting is actually supposed to create a buffer of dead space to keep the fuel suspended and prevent the gas from pooling of the walls
when you grind away the runner material you move the rpm range powerband up a bit but you lose torque especially where most need it in a truck...down in the lower rpm range.... The kegger mod is a trade off at best.

 

Its just air. There better not be fuel in it.

 

Its called a boundry layer....the dimples in a golf ball have a slightly more complex purpose. They serve the same purpose as the stitching on a baseball. They both rely on the spin on the ball. I have researched extensively the properties of mass air flow due to my other hobby. Google somthing called "vena contracta".

 

OK so I installed the Magnaflow y-pipe with new cat and new O2 sensor yesterday. I have not really had a chance to get the truck out and open it up BUT from what little I have driven it I would say it drives like a whole different truck.

So I installed Gibson headers, Magnaflow Y-pipe/cat, new front NTK O2 sensor, FlowMaster cat-back, Harland Sharp 1.7 roller rockers, Kegger mod/Hughes plenum kit, Iridium plugs, MSD 8.5 wires, SCT tuner.

http://i1068.photobucket.com/albums/...0618063919.jpg

 

I am not clear how shortening the runners in the intake effects the torque at lower RPM?

 

Runner length dictates where the engines power band resides. Short runners give high end power, long runners give low end torque. You can have one, or the other, but, not both. With the correct cam/intake/heads, you can have a pretty wide power band, but, there is no such thing as a low-rpm torque monster that also makes good power in the upper RPM range. Shortening the runners on the keg will move your power band up a couple hundred RPM. You don't really "lose" anything, you just move where you have it. (provided runner length is the ONLY change.)

We don't have any hard and fast numbers on just how things change, as I have yet to see a dyno chart that actually starts below 2500 RPM....