Quieter upgrade?

[Sean Buick 76]

Skip the headers only because you want low noise. Run two mufflers in line.

 

[L31MaxExpress]

Yeah, I've read all that.

I still think there's a mistake in his methodology.
1. I replaced an 048 with a 369...can't tell a bit of difference in how the truck runs.
2. The aftermarket sells the same module as a replacement for both of those numbers...and several others. If there was a real difference in ignition timing, I don't know how it would get past the EPA for either emissions compliance, or for CAFE compliance.

OTOH, I'm way too lazy to do a timing-test of the two modules of my own.

There is definitely a difference in them. RBob, Haulin@$$ and myself have all observed almost identical results doing the same testing.

 

[NMNorsse]

Honestly, I don't think the legalities are all that hard. Unlike the coal rollers, no one is going to bust you and confiscate your 35 year old vehicle if you made an effort to keep a catalyst on it. Or two. You'll use one slightly larger one or two slightly smaller ones, so the mass won't make that much difference. Especially since you'll be replacing a very heavy, pan-style converter with a much lighter, honeycomb style. In doing so, particularly if you use 2, you can put them closer to the engine. It's an improvement, not a reduction in its function.

What I'm considering now is getting the Toyota Tundra 5.7 pipes from the header to the muffler which are 2.5" and include 2 small cats per side with a cross over and stay dual until a 2-in/1-out muffler. You can find them for $200, which compared to a y-pipe and high flow cat isn't bad. I'd just have to change the flanges, plug the downstream O2 bungs, and figure out the hangers which isn't a big deal. Then either a 2 into 1 big muffler, or a y to join the pipes and a 1-in-1-out big muffler. If that isn't quiet enough, add a resonator or second muffler after the big one.

My thinking is that 4 smaller and less restrictive cats will help quiet down the exhaust and let it breath better. Toyota has the cats placed closer to the engine so they'll heat up quicker so I may have to add some shielding. They're designed for a higher revving direct injected 5.7 motor so the flow should be adequate for the old TBI 5.7. Since I need a cat now and in the long run I'd put in shorties, I might start with Mr. T's cats tied to the factory manifolds and muffler to see how that goes.

For example:

For 2007 - 2009 Toyota Tundra 5.7L Catalytic Converters Set Left & Right Side | eBay

Not for Use in California. Due to the increased emissions standards.This item is not certified for sale in California and New York. Tube material: Stainless Steel. Restricted States: California, New York, and Maine.

www.ebay.com

 

[jaybee]

Even if you have to cut it up and splice in an extra bend or something, that looks to me like a fantastic plan. The cats are so close to the exhaust ports, you should easily be able to pass a sniffer test if you should have need of it one day.