Exhaust/Emissions Help

[onefstsnake]

Well Im planning for future mods for the Mustang and needed some opinions.

I hear that longtube headers (LT's) will make a larger gain in power than Shorties. And will only continue to make more power after more mods. (i.e. heads, intake)

My biggest question is emissions... Can I run LT's with Cats? I really havent seen many people doing this...(or just never noticed)

Also, I have heard that one of the 2 types are a pain to install, like jacking the engine, removing steering shaft...

I really want the car to sound nice and make more power, but also be able to pass emissions and not scrape the ground.


If these questions have already been answered...sorry for the thread.

Thanks

 

[95GTV8]

LT's are the ones that are PITA to install, jacking up the engine etc. I'm sure about LT's and cats.

 

[onefstsnake]

What about LT's that have separate pipes for each cylinder then fit into a collector?

Im guessing I would have to weld them to the collector which would be hard to do when they are on the car...

 

[$uperstang]

I have Lt's and they fit fine and you can get catted H-pipes or X pipes all day long. It's the best way to go for power.

 

[jrichker]

If emissions testing is a big concern, stay away from long tube headers.

Two reasons:
1.) The O2 sensors are often too far back to work at peak efficiency. The distance between the exhaust valve and the O2 sensor allows the exhaust gases to cool below the optimum point for the best O2 sensor results. That means air/fuel ratios are not optimized for minimum emissions.

2.) Cat converters use heat from the exhaust to work efficiently. As stated above, the long tube headers cool the exhaust gases because the have more surface area. This makes it harder for the cat converters to do their job, since efficiency drops off rapidly as the exhaust gases cool down.

 

[onefstsnake]

Thanks everyone.

jrichker- Would it be possible to weld a O2 bung closer to the heads?
And just weld the original bung closed?

Or maybe I should ask this.

Would a Shorty setup with a high flow H pipe and catback make considerably less power than the same setup with LT's?

And how would this change if I added a decent Intake and maybe a Stroker kit?

 

[WilwoodFiveO]

onefstsnake where excactly are you located in NOVA. I want to check out you car and you can check out my exhaust setup. I'm running MAC LTs into a catted H. I have yet to pass emmision but I think I will do fine seeing how I'm also going to running a whole bunch of BG products through my motor first.

Tyler

 

[onefstsnake]

onefstsnake where excactly are you located in NOVA. I want to check out you car and you can check out my exhaust setup. I'm running MAC LTs into a catted H. I have yet to pass emmision but I think I will do fine seeing how I'm also going to running a whole bunch of BG products through my motor first.

Tyler

Just IM'd you...

 

[stangjunkie]

where in northern VA?? im in loudoun and i know how to get around emissions in a very legal way!!

 

[WilwoodFiveO]

stangjunkie let me now how, my mac catted H is on back order for two weeks and it costs me twice as much as my off road, I would love to run an offroad H if you could get me passed somehow. Let me know, if this works, your the greatest!!!

Tyler

 

[WilwoodFiveO]

Just IM'd you...

Hey sorry man,

Thats my bros screen name, thats just the one listed under the information here at stangnet, its actually his car Im just really building for him and driving it until he gets his liscence in three months. Sign back on and I'll talk to you on my screename which by the way is trr6587. Take it easy man.

Tyler

 

[jrichker]

Thanks everyone.

jrichker- Would it be possible to weld a O2 bung closer to the heads?
And just weld the original bung closed?

Or maybe I should ask this.

Would a Shorty setup with a high flow H pipe and catback make considerably less power than the same setup with LT's?

And how would this change if I added a decent Intake and maybe a Stroker kit?

The length of the individual tubes are the problem. The extra surface area of each tube causes the exhaust gases to cool. If you move the O2 sensor up past where the tubes meet to join the collector, you get the exhaust gases from one cylinder. That does not take into consideration what's happening with the other cylinders.

The difference between long tubes and a quality shorty like the FMS shorty is maybe 5-10 rear wheel HP at mid RPM range. At max RPM, the difference is probably less than 5 RWHP. MM&FF did an article recently and did various exhaust combos. I'll look and see if I can find it.

Any additional bolt ons will increase power, but probably will not increase the difference between long tubes and shortys.

The only simple fix is to wrap the long tubes with header wrap. This causes problems of its own, it tends to make the headers rust quicker.

 

[ExplodingGopher]

I'd say if you had a plasma cutter and a good MIG welder and some extra piping, it would be very possible to make bungs for the O2 sensors and fab up something for the cats.