Exhaust Modification! Help!

[Tim S (Roguemachines17)]

Hi, Im new to the site and I have a 99 X Limited AWD with the 5.0L 302 V8. Ive been looking around and cannot seem to find an answer. I would like to keep all the cats and make a custom cat-back exhaust. From the cats is a dual 2.5" exhaust, and I was wondering what mufflers you guys would recommend for what i plan to do. I want to keep all the cats (because i cant afford new ones and it barely passes emissions as is) and do a flowmaster muffler swap into a single 3 inch pipe out the back without a resonator. Do you think I should go with a Y pipe from the cats and go into a single 2.5 inch in and single 3 inch out... or a put a Y pipe after the muffler ( dual 2.5 in and dual 2.5 out) or what recommendations do you guys have for about $300 and keeping the stock cats. I was also wondering on how to extend the breather tubs for the trans, and diffs
Thanks,
Tim

 

[CDW6212R]

Welcome Tim.

My shortest opinion, given the 302 with GT40 heads and intake; it needs a true dual exhaust, every Mustang 302 has a dual exhaust.

That means two paths for flow, not one at any point, or; the equivalent of two 2.25" pipes area end to end. That is stock mind you, not high performance. No stock Mustang 302 has come with smaller than dual 2.25" exhaust since the pitiful mid 70's cars. Those are all not GT40 engines, these 302's need more airflow.

You can fit two mufflers in the huge space under there which is about three feet long. I see no reason you can't make it a dual exhaust for under $300, my shop here made my single V6 2.5" back half for $100 given my muffler and resonator I brought. Find a shop that can route two 2.25" tail pipes, and choose mufflers that are thin enough to fit stacked. I have a pair of Cherry Bomb Vortex mufflers to go in my newest 302 truck. Those are 4" thick, easily stacked anywhere and unseen.

Note that removing the stock muffler and resonator will make it much louder. Stock mufflers have an internal Helmholtz chamber, which reduces sound a lot. All aftermarket mufflers have nothing like it inside, they are all much louder.

 

[Tim S (Roguemachines17)]

So would you recommend a dual inlet/outlet muffler or two separate mufflers. Also, do you have any idea about muffler silencers. In my neighborhood we have really strict noise complaint people and regulations. I really don't care about the "laws", i just have a few neighbors I like. Any idea on how to silence a flowmaster 40 series muffler down to stock for only a minute or two?
Thanks,
Tim

 

[Craigerz]

I agree, duals all the way back like he said, but if you are keeping all 4 cats I don’t see a need for a turbo style muffler. I don’t think anything will be that beneficial about it besides maybe sound, and if You’re trying to keep quiet.

I did duals back into dual mufflers without the back 2 cats but couldn’t get them high enough for the clearance I wanted, so switched to dual in dual exit, but it’s a lot louder than with the dual mufflers.

Quiet it down for a minute? Idle until you get home for a block or two. With the all 4 cats on I don’t think you’re going to get that pulse and rumble that you think you will.

And I think you’re running 2.25 inch exhaust, unless you want to go bigger.

 

[Tim S (Roguemachines17)]

Do you think removing the secondary cats it will still pass inspection that way ( just rule out the sound )

 

[Craigerz]

Depends on how well it’s kept up. Maintenance, tune and what not. Mine did. The o2 sensors are all in front of the second set of cats so no check engine lights or o2 bung needs to be added or anything special.

But once you remove the second set of cats it does get exponentially louder.

 

[Tim S (Roguemachines17)]

Would it be and issue to run dual 2.5 inch exhaust out of a dual in/out muffler with the cats, then later if i want, remove the secondary cats and just put a pipe to connect the front cats to the muffler?

 

[Craigerz]

Well what are you trying to gain from this? Sound, performance, pass emissions? Do you just need new exhaust?

 

[Tim S (Roguemachines17)]

Right now I have a really bad exhaust leak from the muffler. Im 17 and still want it to pass emissions, but if im gonna buy a new muffler and tail pipe, i wanna do it right the first time

 

[Craigerz]

What’s the shape of your Ex? Others are going to chime in, this site is awesome for help just give it a bit.

Miles? Maintenance? Have you failed the inspection before?

 

[Tim S (Roguemachines17)]

My car was daily driven from 99 to 05. In 05 my granddad took it to Florida as his vacation car. It sat in a garage 9 months out of the year and was daily driven the other 3 from 05 to 17. When we brought it back up, it failed the first emissions test, but after a few hours of driving it passed. It just ticked over 85k today and has always been taken care of. Looks and drives mint except for the exhaust leak. Standard maintenance, (shocks, filters, plugs, spark plug wires, fluids, tires, brakes ect...)

 

[Craigerz]

Sounds like a really nice catch there! I bet it just needs to be driven, besides the exhaust.

Cars don’t like sitting.

 

[Tim S (Roguemachines17)]

Yeah, ive put about 8k on it in 6-7 months or so. So do you think it will pass emissions with the secondary cats removed

 

[Craigerz]

How long has it been since it failed the emissions? The cats only really do their job when they are hot, so when you went back that’s probably why it passed.

 

[Tim S (Roguemachines17)]

also, do you think that with all the cats and a flowmaster 40 series delta flow, it will still have that chambered sound, just quieter?

 

[CDW6212R]

Given the lower mileage, I'd leave the cat pipes alone for now. As said the sound gets louder with each component you remove. But two mufflers will reduce the flow to half going through each, which ought to make it quieter than one muffler.

The tail pipes would be the hard part, I think only an exhaust shop will be able to fit a pair, and two 2.25"(stock size) will outflow one 3" pipe as you'll read others swear by.

Flowmaster mufflers are among the most restrictive, they cost HP. The Dynomax turbo mufflers are among the quietest, and flow fairly well. I'm older now and more and more I want less sound, but I do like the stock Explorer 302 rumble. That's the level I prefer. When I get my pipes fabricated from back to front, I'll build a resonator of my own, a short chamber of maybe 8"x8"x4" in size. Hopefully I can get those to do what the OEM chamber inside stock mufflers do.

Here's a picture of what one of our members here did to fit two tailpipes. I might try that method, as it goes inboard of the leaf springs. But I doubt it leaves room for the spare tire. With the pipes run over the diff, that way, they still could go outside the leafs, like the stock one does on the right.

 

[Craigerz]

Someone else is going to have to answer that one.

 

[CDW6212R]

The Flowmaster 40's will be loud with any cats. Only a special resonator and pair of mufflers might be not loud, but I don't know of a resonator that good. On the Corral forum, there is a huge thread about 1/4 wave pipes, which are extra pipes welded into the pipes behind mufflers, and lead to a capped end, about 28" long.

 

[Tim S (Roguemachines17)]

Thanks for the help, one last question... if I wanted to run a single 2.5 inch out the back with a flowmaster super 40 series single in/out, would I still get a nice sound that is noticeable... also would a Y pipe between the cats and muffler disturb airflow or decrease sound...
Thanks,
Tim

 

[Craigerz]

I think the flow master dual in single out is about the same as a y pipe into a single in/out. It’s not the same as an H pipe trying to balance flow and all that. The Y is just a splice, nothing else.

Easiest thing to do is wack the old muffler off, leave all the converters, dual in single out flow master. Exit where ever you want. Might be a little louder but probably not noticeable. Def won’t cost 300 bucks.