Magnaflow Y-Pipe Cat Flange?

[99'Subourbon]

Hey All,

So when I looked under my truck, I noticed I have the double to single Y setup, unlike the magnaflow double Y setup. Does anyone know where I can get an additional flange to mate to it so that I can get a custom exhaust dome?
This is the product I am looking at; Magnaflow Y Pipe Cat Direct Fit

On a different note, do I need this? I want to go LT's, but I also want to stay emissions legal, so I need cats and pre/post o2 sensors. Would it be cheaper to get a pair of coated LT's and 2 high flow cats, then have a shop weld up the rest? I want enough flow for 325rwhp (KN Drop in filter (and a fabbed up smooth tube from box to tb), LT4 Cams, LTs, Full exhaust, and Tuning).

Thanks!

 

[99'Subourbon]

Alrighty

 

[Blind]

your muffler will have the mating flange to match and bolt up to that magnaflow, have you looked under your truck?

If you go LT's, depending on your state you won't pass visual smog. For example in CA you won't.

The stock stuff from my truck -

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The magnaflow CA legal stainless Y-pipe on the truck -

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The magnaflow stainless catback compared to the stock setup -

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The mods you listed will not make 325rwhp either. A stock `96-`99 5.7L truck makes about 205rwhp, a filter, exhaust, and LT4 cam will not make an extra 120rwhp, 325rwhp is about 400hp at the crank...that's not going to happen without boost or more cubes, especially not with the stock intake, injection system, and heads.

 

[99'Subourbon]

your muffler will have the mating flange to match and bolt up to that magnaflow, have you looked under your truck?

If you go LT's, depending on your state you won't pass visual smog. For example in CA you won't.

The mods you listed will not make 325rwhp either. A stock `96-`99 5.7L truck makes about 205rwhp, a filter, exhaust, and LT4 cam will not make an extra 120rwhp, 325rwhp is about 400hp at the crank...that's not going to happen without boost or more cubes, especially not with the stock intake, injection system, and heads.

Odd, I read somewhere on this forum that with full header back exhaust, lt4 cams (beehives, 1.6 roller rockers, etc) and a tune 325rwhp was attainable. On another note, yeah I looked under my truck and it Y's into a single before the flange.

 

[99'Subourbon]

Here's that thread http://www.gmt400.com/forum/showthread.php?10906-What-mods-can-1000-do-for-a-1998-Vortec-5-7

 

[SCOTTYINWV]

I would order a set of mid length or Lts with collectors included and high flow cats to fit your setup, I think yours has a o2 in one of the cats And have it done custom. As far as coated headers, i would buy a set of bare steel or painted ones. Blast them and coat with vht header paint and wrap them. I would also wrap to the cats to help keep some heat in the exhaust. When I redo my setup with headers, i plan on double wrapping the system all of the way to the mufflers to cut down on some heat. (I'm catless...)

 

[99'Subourbon]

Here's what it looks like - is this a 3/4 ton setup?

I would order a set of mid length or Lts with collectors included and high flow cats to fit your setup, I think yours has a o2 in one of the cats

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And have it done custom. As far as coated headers, i would buy a set of bare steel or painted ones. Blast them and coat with vht header paint and wrap them. I would also wrap to the cats to help keep some heat in the exhaust. When I redo my setup with headers, i plan on double wrapping the system all of the way to the mufflers to cut down on some heat. (I'm catless...)

Is there a set you could recommend? For some insight, I plan on putting in 4.56s and want as much low end as possible. I plan to tune for Towing and In-Town Economy.

None of the 02s go directly into the cat; they are pre and post.

Driver First

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Driver 2nd

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Passenger 1st

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Passenger 2nd

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[Blind]

that setup is totally different from mine so I'll have to assume it's a 3/4 ton - that looks like 3" pipe after the Y, maybe 2.5" before it?

the linked thread looks full of people making assumptions with no facts, the guy who claimed that an lt4 cam, exhaust, and tune would be good for 325hp on the first page didn't even know if the stock heads would need machine work to function with the lt4 hot cam (which it does, the L31 heads can only support 0.475 lift without work) so it's pretty obvious that he doesn't have that combo in a truck with a dyno to show it's worth.

A stock LT4 corvette makes 280-290rwhp on a dyno, and those heads flow better than L31 heads

LT4 heads flow 250 intake and 172 exhaust @ 0.500 lift
L31 heads flow 239 intake and 160 exhaust @ 0.500 lift

fwiw I have a pretty stout combo in my tahoe (HT383E stroker crate motor, MPFI, full exhaust, e-fan, underdrive pulley's, airaide intake) and it feels no where near 325rwhp, 280rwhp maybe.

 

[99'Subourbon]

that setup is totally different from mine so I'll have to assume it's a 3/4 ton - that looks like 3" pipe after the Y, maybe 2.5" before it?

the linked thread looks full of people making assumptions with no facts, the guy who claimed that an lt4 cam, exhaust, and tune would be good for 325hp on the first page didn't even know if the stock heads would need machine work to function with the lt4 hot cam (which it does, the L31 heads can only support 0.475 lift without work) so it's pretty obvious that he doesn't have that combo in a truck with a dyno to show it's worth.

A stock LT4 corvette makes 280-290rwhp on a dyno, and those heads flow better than L31 heads

LT4 heads flow 250 intake and 172 exhaust @ 0.500 lift
L31 heads flow 239 intake and 160 exhaust @ 0.500 lift

fwiw I have a pretty stout combo in my tahoe (HT383E stroker crate motor, MPFI, full exhaust, e-fan, underdrive pulley's, airaide intake) and it feels no where near 325rwhp, 280rwhp maybe.

Good to know - thanks for the info. For power, what I intend to do is; efans, drop in filter with a custom smooth tube from box to TB, LT4 Cams (or equivelant, beehives, 1.6 rockers etc to make the cam work without machining), LTs, and Full header back exhaust with custom tuning. Whatever that gets me, I'll be happy with. 33's with 4.56s should make it feel spry enough.

 

[99'Subourbon]

On another note, it does look like 2.5" to 3" at the Y - you think this flows well enough stock that I could just replace the cats with high flows and run a 3" si/so muffler and be good (after my listed intended upgrades)? Then I could just replace the headers, and have a shop mod it up to fit with stock y-pipe.

(Although replacing it all would cut some weight from this brickhouse)