Dual inlet high flow cat or 2 high flow cats?

For a small block that likely won’t be spun past 5000 rpm regularly, the single should be fine. Just removing the old GM pellet style converter is a big plus, they were pretty restrictive when new.
Patrick

Dual cats. Cats work best hot, as in close to the header. Running the single cat means a crossover pipe, under the oil pan so that at least the passenger bank is what's heating the cat. That's a considerable amount of customized piping to get it true and right, if you have the right oil pan, otherwise the piping hangs very low right there.

It's generally easier with headers to run dual exhaust, which can benefit with a sbc from an H pipe. Give the low end torque a bump.

Don't know where you live, but if you live in CA, you will have to stick with the single cat, as that was what came with the car. Otherwise, cats need to be sized based on flow, so 1 single cat for 350 cubes or 2 dual, each sized for about 175 cubes. Sizing is necessary to get the cat hot enough to work.

What darbysan said.

darbysan said:

Don't know where you live, but if you live in CA, you will have to stick with the single cat, as that was what came with the car. Otherwise, cats need to be sized based on flow, so 1 single cat for 350 cubes or 2 dual, each sized for about 175 cubes. Sizing is necessary to get the cat hot enough to work.

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I am in ca but I’m moving to florida in 2 years and I found away around the smog until then.

Karadjgne said:

Dual cats. Cats work best hot, as in close to the header. Running the single cat means a crossover pipe, under the oil pan so that at least the passenger bank is what's heating the cat. That's a considerable amount of customized piping to get it true and right, if you have the right oil pan, otherwise the piping hangs very low right there.

It's generally easier with headers to run dual exhaust, which can benefit with a sbc from an H pipe. Give the low end torque a bump.

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Thanks low end torque is what I need

Heisenbergselcamino said:

I am in ca but I’m moving to florida in 2 years and I found away around the smog until then.

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I spent over 20 years in Fla, finally getting the chance to get out. Best decision the wife and I ever made. It was a mess when we left 20 years ago with all the sinkholes, lack of home insurance as the companies all pulled out and rising crime rates. It's a total disaster right now.

Heisenbergselcamino said:

Thanks low end torque is what I need

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First, are you running fuel injection? Cats need to have the air/fuel ratio tightly controlled, feedback from O2 sensor in the collector.
I'm currently running FI 350, headers with cats right behind the headers, then H-pipe, then mufflers. Works well enough to be a daily driver.

Karadjgne said:

I spent over 20 years in Fla, finally getting the chance to get out. Best decision the wife and I ever made. It was a mess when we left 20 years ago with all the sinkholes, lack of home insurance as the companies all pulled out and rising crime rates. It's a total disaster right now.

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Damn. Well maybe not Florida then. But definitely somewhere down south. If you have any recommendations I’d love to hear

greywolf said:

First, are you running fuel injection? Cats need to have the air/fuel ratio tightly controlled, feedback from O2 sensor in the collector.
I'm currently running FI 350, headers with cats right behind the headers, then H-pipe, then mufflers. Works well enough to be a daily driver.

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No fuel injection. Carbureted motor. Headers will be wrapped with exhaust wrap. I think that’ll help heat get to the cats and them to work better and help my engine bay. I’m adding borla mufflers and I’ll probably add an H pipe too because I need low end torque. My car is also an 80’s gm car so when I swap the stock manifolds I’ll have to delete most of the smog stuff, I want to make sure I do a proper job at that. Also should I install my headers myself then have the shop do the rest or will an exhaust shop do headers. I know I can install headers myself but driving there with open headers seems a little obnoxious I don’t wanna get pulled over.

Wrapped headers tend to rust overtime. Consider Ceramic Powder Coat. Keeps the heat in the pipes, looks good, and lasts. For Torque, consider changing rear gear ratio. Will feel like you've added 100 hp. That's the best performance mod on a stock engine.

I would say do the headers yourself, if you can. Only because it's easier to wrap them when not on the engine, and you'll need to test fit for clearances with other components like the steering shaft. Tossing on some pipe and clamping on the mufflers after the collector isn't too difficult, it's only temporary. That'll cut down on a lot of labor costs in shop time if the exhaust shop has an easy bolt to collector starting point.

darbysan said:

Wrapped headers tend to rust overtime. Consider Ceramic Powder Coat. Keeps the heat in the pipes, looks good, and lasts. For Torque, consider changing rear gear ratio. Will feel like you've added 100 hp. That's the best performance mod on a stock engine.

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Hmm, what if I did both as far as ceramic powdercoat and wrap. It shouldn’t rust with the powder coating and I’d imagine with the power of both I’d get some great heat resistance

Karadjgne said:

I would say do the headers yourself, if you can. Only because it's easier to wrap them when not on the engine, and you'll need to test fit for clearances with other components like the steering shaft. Tossing on some pipe and clamping on the mufflers after the collector isn't too difficult, it's only temporary. That'll cut down on a lot of labor costs in shop time if the exhaust shop has an easy bolt to collector starting point.

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Forsure that’s what I was thinking, however from stock it’s only a single exhaust pipe, so I couldn’t just clamp it up for the ride to the shop. I’d have to run open headers. I know a buddy who stuffs t shirts into his cars exhaust pipes when he pulls into his girlfriends neighborhood to quiet it down. Maybe I could just do that