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Old 01-20-2014, 02:05 PM   #1
lucky_7
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Need help with Exhaust!

Hey guys,

I need a little help installing exhaust for my 98 5.7 ext cab sierra. Currently Im looking at a flowmaster super 50 series , 2.25'' dual in/3.00'' center out with a turn down. I just need to know the stock exhaust size coming from the cats so can buy the right adapters. Later I plan on doing some engine mods and going with headers and true duels with and x pipe and 2 flowmasters.
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Old 01-22-2014, 03:53 PM   #2
TheBlueBomber
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Re: Need help with Exhaust!

I believe stock exhaust is 2 1/4" all the way through. That was what was on my '96 when I bought it.
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Old 01-22-2014, 06:25 PM   #3
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Re: Need help with Exhaust!

thanks, guess i could use my calipers to measure the outside and subtract the wall thickness......duh
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Old 01-23-2014, 10:49 PM   #4
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Re: Need help with Exhaust!

my 97 ecsb Z71, right at the dual inlets of the stock muffler each pipe is 1 7/8", i'm sure its same up to cats. 2" id to 2.25" adaptor will leave a small gap to fill with the welder on the original pipe.
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Old 01-23-2014, 11:42 PM   #5
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Re: Need help with Exhaust!

Yup, I measured them earlier and they are 1 7/8", from the muffler to the cats and I'm sure they are the same to the manifolds.
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Old 01-24-2014, 01:22 AM   #6
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Re: Need help with Exhaust!

Thank God you didn't listen to me then haha.
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Old 01-28-2014, 03:50 PM   #7
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Re: Need help with Exhaust!

hehe, ya, but thanks for trying bluebomber
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Old 01-29-2014, 02:21 PM   #8
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Re: Need help with Exhaust!

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Originally Posted by lucky_7 View Post
hehe, ya, but thanks for trying bluebomber
My manager always says... "It's not about if you win or lose, It's how you prepare for the game".....

I guess I made him proud on this one.
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Old 06-09-2014, 06:17 PM   #9
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Re: Need help with Exhaust!

Anybody know of a store bought y collector that will fit on the pipes behind the cats?
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Old 06-09-2014, 06:38 PM   #10
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Re: Need help with Exhaust!

You will probably have to have it made at the muffler shop of choice...Ive looked for a y pipe... If your going to change it later why not just wait and do it then?

I went and replaced the front pipes with a flowmaster kit and high flow cats, now im adding this. http://www.summitracing.com/parts/wlk-54020 and two Aerochambers dumped over the rear axle...........


Im running a DI/SO flowmaster 50 series now.... Me no likey
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Old 06-09-2014, 06:39 PM   #11
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Re: Need help with Exhaust!

Thanks blue...
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Old 06-12-2014, 11:07 AM   #12
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Re: Need help with Exhaust!

Does anybody now if I can completely remove the cats from a 97 5.7 liter, I can only see one set of o2 sensors in front of the cats, and I have been told that its okay like that. But Ive also been told the truck will still run a little rich with the cats removed?
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Old 06-12-2014, 12:18 PM   #13
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Re: Need help with Exhaust!

On my 97,I went with the 50 series then 4" chrome tips out the back,way too loud for a stock engine. Have since added baffles in the 4" tips,now it sounds good. Didn't notice any change in performance or mpg.
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Old 06-12-2014, 12:23 PM   #14
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Re: Need help with Exhaust!

where were your o2 sensors at before, and did you remove the cats?
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Old 06-12-2014, 12:29 PM   #15
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Re: Need help with Exhaust!

I left them on. I wouldn't remove them unless they're going bad.
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Old 06-12-2014, 03:11 PM   #16
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Re: Need help with Exhaust!

what about high flow cats? truck has 120k on it now and since im already here i might as well replace them right...
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Old 06-12-2014, 03:21 PM   #17
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Re: Need help with Exhaust!

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Originally Posted by lucky_7 View Post
what about high flow cats? truck has 120k on it now and since im already here i might as well replace them right...
Yes........ I installed the Flowmaster kit and have seen improvements in sound and HP, Not a lot but its noticeable.
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Old 06-12-2014, 03:40 PM   #18
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Re: Need help with Exhaust!

thanks guys,

Well i found a 50 series delta flow the other day in the junk yard, paid 35 dollars for it, it 3''in/3''out, so im not ever sure in i can use it without having a custom y pipe made to come from the cats to the muffler.

If I were to buy a high flow cat at 3''in/out, I could just have them y it at the bottom of the drop pipes and tuck the cat nicely, then I could (weld this myself) extend 3'' pipe straight back to the flow and put a turn down on it....

I would get both a new cat, and a new muffler, for around......let see

100.26 +tax for the cat
35.00 for the muffler
maybe 100. to install

thats only 235.+/- for a complete system...
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Old 06-18-2014, 11:38 AM   #19
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Re: Need help with Exhaust!

Anybody have a diagram of the o2 sensor locations on my truck?
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Old 06-18-2014, 01:28 PM   #20
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Re: Need help with Exhaust!

Quote:
Originally Posted by lucky_7 View Post
Anybody have a diagram of the o2 sensor locations on my truck?
I'm at work but let me see what I have on the comp at home. I just did all 4 of mine . Pretty simple , just a plug and play deal.
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Old 06-18-2014, 05:25 PM   #21
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Re: Need help with Exhaust!

Okay thanks, Ive looked for them behind the cats, and i cant see them anywhere, just one on each down pipe...
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Old 06-18-2014, 05:43 PM   #22
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Re: Need help with Exhaust!

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Originally Posted by lucky_7 View Post
Okay thanks, Ive looked for them behind the cats, and i cant see them anywhere, just one on each down pipe...
Hope this helps.
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Old 06-18-2014, 07:53 PM   #23
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Re: Need help with Exhaust!

Thanks, I'll go look at it now
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Old 06-18-2014, 10:13 PM   #24
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Re: Need help with Exhaust!

Well I found them, I have four, , so no high flow cats for me, I'll just put on a nice flowmaster with aggressive sound to overcome the restriction from the cats....
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Old 06-18-2014, 10:18 PM   #25
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Re: Need help with Exhaust!

What's a good aggressive sounding flow for the 5.7 Liters?

I did a little looking, maybe a super 40?

Last edited by lucky_7; 06-18-2014 at 10:40 PM.
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