My 454 Rebuild

[OutlawDrifter]

Frieburger has an Engine Masters 2.5" vs 3" exhaust video on youtube. They are using a 620hp solid roller 454. The part I find comical is where they are discussing it being ran wide open and how the power under 3500rpm picked up with the 2.5" exhaust doesn't matter. And it only lost 20hp with full 2.5" exhaust that's a 3% loss over open headers with extensions, and I would be less on lower HP engine/setup.

A 620hp solid roller carb'd BBC doesn't really match a cammed Vortec 454 with stock injection that will spend most of its life under 4k rpm.

Optimizing the scavenging where the engine spends 80%+ of its time is important when building the exhaust system.

I take a different approach for our dirt track hobby stocks, than I do for my daily drivers.

 

[Supercharged111]

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.

My 454 trucks are 3" precat and 2.75" post. Coming right off the manifold it's closer to 2.5" or so, then flares out to 3". I believe the 350 8 lug trucks got the same for Vortec trucks.

 

[Spareparts]

Exactly. My engine will be under 4k most of its life. Being a stock bottom end i dont like turning it over 4.5k but i have hit 5k a time or two making data logs.
Exhaust needs to be optimized for the 1k to 4.5k rpm range.
I can say that from about 1.2k to 4k it pulls pretty dang hard for being mostly stock.

 

[L31MaxExpress]

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

On the vans it is not except perhaps at the manifold flange end of the head pipes.

 

[Piratehunter]

behind the jbs's, my '97 has dual 2.75" through the cats up to the single Magnaflow with dual 3" inlets and single 4" outlet behind rear wheel. sounds real healthy, so people tell me, without the sound being obnoxious in the cab. I think it sounds awesome thundering up through the narrow canyon walls on hwy 24.

 

[Mangonesailor]

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.

Measured today. 3" from headers until after mufflers, then 2.5" to the back with 4" tips.

It's fine.

 

[BNielsen]

Measured today. 3" from headers until after mufflers, then 2.5" to the back with 4" tips.

It's fine.

Why is it that my exhaust is super similar to yours but my truck sounds like a$$? No headers and I still have cats though.
Are the Magnapacks really just that good?

 

[Mangonesailor]

Why is it that my exhaust is super similar to yours but my truck sounds like a$$? No headers and I still have cats though.
Are the Magnapacks really just that good?

Well, it's basically a glass pack, and glasspacks are, well, glasspacks. Flow enough exploding air through them at the right size and it sounds great. Flow it quickly and without a bunch of turbulence (headers, no cats) and it sounds even better.

A 80 series or super 40 also sounds good with a lot of displacement.

I'm sure there's other nice combos out there for our trucks

 

[OutlawDrifter]

Measured today. 3" from headers until after mufflers, then 2.5" to the back with 4" tips.

It's fine.

That 2.5" pipe after the mufflers is aiding in keeping the gasses fast and hot, increasing your scavenging. Dual 3" out the back is a different animal, and would be less than optimal. I don't doubt your setup works great on your pickup.

Well, it's basically a glass pack, and glasspacks are, well, glasspacks. Flow enough exploding air through them at the right size and it sounds great. Flow it quickly and without a bunch of turbulence (headers, no cats) and it sounds even better.

A 80 series or super 40 also sounds good with a lot of displacement.

I'm sure there's other nice combos out there for our trucks

80 series is the crossflow muffler for 3rd and 4th gen F-bodies and is probably the worst flowing muffler in the history of crossflows(I can say this having run one on my car when it was a stock L98 350).

Chambered vs absorption muffler is a debate for the ears. Everyone has a specific sound they like.

 

[Scottm]

When I modified some ebay stainless headers, I put on v band clamps and extended the 3 inch collector by 10 inches or so before reducing into 2.5. The longer collector lets the pressure pulses expand more, increasing the suction pulse going back to the head. Supposably.