Trying to find a good sound on youtube and dam almost all sound good!
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Then I must be remembering wrong. I'll need to measure because I'm very certain I did not make it overly massive and just for the sound.Dual 3" is huge for a street driven torque oriented vehicle.
Dual 3" is huge for a street driven torque oriented vehicle. The change from 3-2.75" isn't increasing ANY back pressure. In fact it's probably helping the scavenging effect by keeping the exhaust moving quickly and not cooling off as fast. It takes big HP and lots of revs to push dual 3" exhaust. The Magnapacks are giving you that old school glasspack rap. I won't argue that it probably sounds great, as I have a similar dual 2.5" setup on my LS powered '49 GMC, instead of Magnapacks, I've got the longest 4" case Thrush glasspacks they make.
Again, I think this is overkill, and all it will be is loud. This is just my opinion, based on the fact I have built dozens of different exhaust systems, and read up on as much exhaust theory that I could absorb.
WHY delete the rear O2 sensors if you're keeping catalysts?If a guy wanted to delete the rear o2 sensors in the tune what all needs to be changed?
Im finally thinking it's time for some shortie headers into high flow cats and dual exhaust with a H pipe.
Dual 3" is what my 97 Van with the L31 came with from GM from just off the manifolds to the muffler. I put a dual 3" in/single 4" out muffler and 4" tailpipe on it years ago. The old 350 could not have been happier. I then put shorty headers on it to address cracked manifolds. I later swapped out the shorties for Thorley Tri-Ys and the stock cats for 3" highflows which gained additional torque over the muffler/shorties. Granted if I had built the exhaust from scratch it would have been 2.5" dual to single 3.5" with a merge Y.
This is right after I put the Tri-Ys on it. No shortage of torque moving 6,200 lbs with a 4L85E and 3.73 gears. I was only reving it like 4,800 rpm.
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I've never seen anything bigger than 2.75" from GM on the headpipes. Even so, those large sewer pipes went back to a restrictive OEM muffler, negating any gains that might have been had.
I don't doubt the 350 was happy, but I bet you left some on the table with the 4" tail pipe and 3" headpipes, the 2.5" dual to 3.5" would have been more ideal for sure.
Exhaust theory is all about keeping the fine line between heat and flow to create better scavenging.
I think long tube headers into 2.25 or 2.5 to a merge Y and single 3" is tough to beat for the average small block be it 305 or 350.I think 2.5" is perfect for a 350 with a moderate cam. Since you have a 454 I'd go with 3". A helmholtz resonator like @OutlawDrifter showed isn't a bad idea.