Just wanted to show you guys why I’m doing this stuff. Figured a cutaway would be a good place to start with the manifolds. These are actual Duramax manifolds we cut in half.
The top one is the stock one, and the bottom one is mine. Of course I picked on the drivers side because it looks the worst on the outside, but I was still shocked at what I found. I’ve numbered the “problem” areas to explain my thoughts on them.
#1. Notice how the runner is actually smaller than the port opening itself
#2. This little “crook” in the casting was a feeble attempt to direct the exhaust rearward I guess
#3. No “crook” here. If you look at it you can even see where some of the exhaust might actually be diverted the wrong direction because of the dimple for the steering column
#4. This is what I call the old right angle “dump and run”. #3 suffers from this also.
#5. This one and #6 really get me. Notice how large the main runner is here with only 2 cylinders in the manifold so far
#6. Now notice how small the main runner is here after 3 cylinders
Now spend a little time looking at mine. I can find a couple of flaws in the design, but I hope you can clearly see why mine will flow better.
Now lets move on to the up pipes. Click on the Read More button for the rest of the story.
The factory stuff is built out of 409 1/16th stainless. Ours are 1/8 304 stainless.
1. Their bends are stamped, fabricated, and mig welded. Ours are mandrel bent and tig welded.
2 Their bends are also on a very tight radius. This caused flow restrictions and turbulence.
3. Their tubes have dents and dimples all over them. These also cause restrictions and turbulence.
4. Their bolt holes are huge to allow for easy assembly and compensate for tolerances. Unfortunately, they don’t do a very good job of aligning the actual exhaust ports.
5. And finally the bellows. Theirs restricts the flow of 4 cylinders down to 1 5/16″. Ours maintains 1 3/4″ through a much better flow liner.