454 exhaust on my 350?

[2002maniac]

Was this ever a factory option?

I was changing a bad midpipe flange gasket on my 99 suburban 2500 5.7 and the guy at the parts store brought out the new gasket for me and it was obviously not the same. It had smaller holes that were spaced differently. The guy was like, "Are you sure it's not a 454?". I said that I was positive it was just a 350 but grab that gasket just for kicks. Sure enough the 454 gasket was identical to my blown out POS.

I got under the truck again and it looks like it has the full 454 exhaust setup aft of the manifolds. Dual 2.5" pipes all the way to the rear muffler with 2 staggered cats in between (1 in fwd of flange, 1 aft). I wouldn't have even thought the downpipes would bolt up to the manifold. It does not look like a custom job which leads me to assume that it was a factory install or that the manifold outlets are similar enough that someone was able to do the swap without any hacking and welding.

I double checked all the RPO codes and did not see anything that looked related to the exhaust.

Anyone experience this?

I was planning on a full exhaust to add a bit of power but this system looks like it should flow quite well! Maybe I'll just throw a 3" magnaflow out back for the sound.

Yes, I'm absolutely certain that it's only a 350.

Here's the 454 front cat section:

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350:

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[michael hurd]

I know the 8600 gvw 3/4 ton 5.7 pickup gets a much bigger y-pipe with staggered cats. The gasket is much bigger than the lighter duty 2500, all the parts stores around listed the wrong gasket, had to get it from GM for my brother when he had his system apart.

 

[98_k1500]

Mine actually measure just a hair under 3". i have a 8600 gvw 3/4 ton / 350. I need that gasket and doughnut gaskets also. When i added to my pipes, a piece of 3" exhaust tubing slid over the existing pipe perfectly. I have the exact same setup you do.

 

[2002maniac]

Very cool. I guess these 5.7 2500 trucks need all the help they can get to deal with the extra weight!

 

[TylerZ281500]

wasnt it the heavy 3/4 got lower compression as well

 

[98_k1500]

Mine has got a 310 horse crate engine in it... seems like they got dished pistons instead of the regular vortec "flat tops"

 

[GMRedline]

I was under the impression that all 3/4 ton and higher GMT400s had the larger exhaust systems independent of the engine type.

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[98_k1500]

^^ me too.

 

[Wagonbacker9]

I was under the impression that all 3/4 ton and higher GMT400s had the larger exhaust systems independent of the engine type.

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