Thanks guys, good stuff. Should have stopped by to see you guys down south, didn't think of it. Decided on not installing cutouts and I am thankful for all input on the topic too. IT will save money, cut down on fab work, save space, and whatnot.
Not too much of a progress update recently, got busy with some other things.
I did get some time to cut out some sections of the oem frame-rails on the passenger side of the transmission tunnel. There is no other way to truly tuck a 3" collector along the area of the 700r4 transmission and the design of the oem inner "frame-rail". stick shift guys have more space and those with smaller automatic transmissions, but not me with the 700r. But, No need to be alarmed, as I immediately used very beefy angle iron to reinforce the remaining frame rail and welded this angle iron to the floor-pan sheet-metal. I also welded a reinforcing flat plate in place on top of hte angle iron too, so it is strong and all stitched together. Once the final placement/fitment of the 3" collector pipe is in place, I am probably going to add a type of triangle brace into the framerail also. I still have to wait to do all that until I build a full transmission cross-member from scratch, so I have some work cut out for myself. No photo updates for now, and taking that much metal out of the frame was a bit scary, but I assure you guys that I welded a lot of reinforcement to make up for the removed frame. keep in mind that I have the subframe connectors coupled to extra bars that go to the rocker area and another section where a sandwich-plate bolts through the floor...along with a full 6-point roll bar. The reason I did all this, is simply to retain ground clearance with the entire exhaust. There was no other way to do this without notching/removing the section frame. I am certainly not the first person to do this, but it is a path less traveled.
after Speaking with some knowledgeable people, I decided to get some sections of that "flexible" 3" pipe...(which is still surprisingly rigid!). This is simply to allow an element of FLEX in the entirety of the exhaust pipes, while the engine torques and twists, and the car travels along the road/tracks. Lots of stories about cracking welds, exhaust leaks, and stuff because of rigidity in the entirety of the pipes, and this has been the culprit of a lot of people having crazy efi/tune issues; even running way rich via ecu fuel correction and killing oxygen sensors. While the flex pipes are unsightly, I think that these flex sections will be beneficial. I made sure I got the kind that are braided on the outside, but fully lined inside the pipe.. not the cheap-o kind.
https://www.summitracing.com/parts/sum-643030. These will go after my o2 sensor, but before the two 3" pipes join to the 4" mufflex exhaust. (using hat flowmaster scavenger 3"to4" merge)
Regarding the oxygen sensors, I was never a fan of where the sensor bung was in those Dyno Dons headers. I wish the bung was a little further back in the collector so it got a "blend" of the 4 cylinders, instead of just the two cylinders nearby it. (Its not visible in my above photos due to the angle I took the picture at, but its just real close to the edge of the primary pipes in the small merge) Anyways, this always seemed to cause a bouncy/erratic AFR reading... that probably was just due to the firing order and exhaust pulses. Along with the holley sniper's wideband oxygen sensor, I use the highly recommended HBX-1 oxygen sensor extender, which is a MUST do for nitrous.
-- my question for you guys is about oxygen sensor placement. I've read a bunch about it, and know that it has to be upright or at the very least, angled so that it can't retain moisture. We don't need to discuss that.... My question is more about how far back from the collector it can be? Since I will not have exhaust cutouts, there will be no chance for ambient air to give a false-reading through the backside of the exhaust system. It is very crowded under these cars, and I want the sensor in a safe spot, where it can get accurate oxygen count readings, and the closest I can get to weld a bung onto a collector pipe is 17-18" from the very end of the ending edge of the primary pipes. * This is exactly where the oem transmission mount/crossmeber is... and is the best chance I have with enough real-estate to install the bung/sensor. Is this too far back? One oxygen sensor will run the holley sniper efi, and I plan on adding in a second o2 sensor so I can finally have some type of reading of what the passenger side of then engine is actually doing. This will go to a gauge in the A-pillar, because the sniper can ONLY use one o2 sensor for its calculations... but I can compare the left bank with right bank in my brain and probably have enough length in the o2 wires to switch them side to side for comparison.