My 454 Rebuild

[Spareparts]

Trying to find a good sound on youtube and dam almost all sound good!

xc_hide_links_from_guests_guests_error_hide_media

 

[Mangonesailor]

Dual 3" is huge for a street driven torque oriented vehicle.

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.

 

[L31MaxExpress]

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.

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.

xc_hide_links_from_guests_guests_error_hide_media

 

[Schurkey]

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.

WHY delete the rear O2 sensors if you're keeping catalysts?

 

[Spareparts]

Because i bought HPTuners and im gonna get my moneys worth out of it.

 

[OutlawDrifter]

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.

xc_hide_links_from_guests_guests_error_hide_media

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.

 

[L31MaxExpress]

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.

Some of the vans are 3" OD when measured and I agree on the OE muffler being restrictive especially with the OE crimped down over the axle 2.75" tail pipe. The 454 and 8.1L vans have the same 3" tubing, cats and muffler. The muffler swap was low hanging fruit to add power everywhere. Backpressure is a power and efficiency robber. With the tri-ys and sewer pipe exhaust the 350 made 330 tq @ 2,900 at the tires through a 4L85E and 9.5" 14-bolt. Relistically I do not believe the 2.5 to single 3.5" would have drastically changed power atleast at WOT although it may have helped part-throttle torque a bit by adding scavenging. I actually plan to build just that exhaust setup someday in the nearer future. I will Y the pipes together right after the cats where the exhaust is the hottest. I had the 2.5 to single 3.5 on my 1st generation Titan and it loved the setup. It might have done slightly better with a single 3", but it already had real issues planting the torque and was cutting a 1.9x 60' on P305/50R20 street tires with an open diff. I lost a touch of mid-range torque (like single digit losses) but actually gained torque down in the 2,000 rpm range as well as nearly 20 hp up at the shift point and the truck was nearly 4 tenths quicker down the track. That was on a slightly smaller 5.6L. The 383 in the van is larger CID and makes more power than the 5.6L did so that setup should work even better for scavenging. The surprise to me was how much power it gained over peak, I have seen mild cams not increase the top-end power as much.

You must be registered for see images attach

 

[Erik the Awful]

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.

 

[L31MaxExpress]

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.

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.

 

[Spareparts]

This is about 454's not 350's. Two different animals and surely 350 exhaust is different from a 454 exhaust.