Exhaust system: dual or single

[catharsis]

Originally Posted by LSxJunkie

I like what the 350Z guys do with their single exhaust and bumper tuck. It makes sense, seeing as 90% of them are still running an exhaust with a Y-Pipe after the cats. Unfortunately, they mostly have awful burnt titanium tips.

I <3 burnt tip. But I'm not digging the coffee can I want something that's a little slimmer like this

[vivix]

Duals are lame on a car like this. Itll look good with a single conversion, something like a flat black vibrant muffler at the back.

[Maxim]

There's really no point in having duals on this car...and the stock muffler set-up looks to be pretty restrictive. Lots of direction changes for the gas flow.

That being said, I will want to switch to a single pipe. High flow cats, and a nice flow through muffler. Sane diameter tip with no resonating chamber, because I do not want my car to sound like whale flatulance.

It's going to be slightly more complicated in this car though I think...I fully intend on purchasing the BRZ Limited with all the goodies, and that includes the aerodynamic underbody cover. It remains to be seen how much that will interfere with aftermarket exhaust layouts. I'd prefer not to have to cut into it to make the muffler fit, but that might be required to avoid melting a portion of it if I switch to a single side and do not use the space devoted to the muffler in the stock set-up.

I'm envisioning something similar to the silver Z car on this page...minus the coffee-can sizing of course.

[86design]

I agree with most of you for the car only being a in line 4 you only need one exhaust...the dual is just styling looks...if it was a v6 that's a different story...when I get my BRZ I'm planning on doing a single exhaust then maybe later on down the road I'll get a dual from. Hks or greddy

[jedichimp]

TRD Quad! Weight schmeight...

[merlin2111]

Originally Posted by jedichimp

TRD Quad! Weight schmeight...

haha i was about to post that but you beat me too it.

In reality though I would go for dual with either single or double tips. I dont like huge exhaust exits so 2 medium sized exits or 4 smaller ones would be my choice.

[old greg]

Originally Posted by jedichimp

TRD Quad! Weight schmeight...

Go big or go home.

[Dimman]

Originally Posted by WingsofWar

Titanium true duals for ballerific status XD

Getting back to the Titanium for a second, some questions for the engineering guys with regards to what kind of fatigue issues a thin (20gauge/.035"wall) 2.500" or 2.750" diameter titanium exhaust would need to worry about.

(please ignore math failure I make about wall thicknesses...)

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Basically if the 1/16" wall 1" tube can survive that amount of deformation, and titanium has a good fatigue resistance reputation, is it something that I will need to worry to much about, since heat and vibration are different than just being squeezed in a vise?

[Homemade WRX]

without watching the whole video, did he ever comment on what grade he was using? I'm guessing Gr5...really common and does well with heat.

[switchlanez]

I picked dual for aesthetics. If I ever build for track then I'd def want a single.

[Quantum]

Single full titanium exhaust, including piping. Should be less than 10lbs and I'll guesstimate stock one will be 40-50lbs.

-Hong

[old greg]

Thanks for the shout out.

It's "Ah-Crop-Uh-Vich" btw.

Anyway, your test isn't really applicable to fatigue life for a couple of reasons. The big one is that fatigue strength @ half of a cycle is always going to be the same as ultimate tensile strength. The issue you are actually worrying about is that there are little bits of titanium oxide/nitride etc. in the filler and HAZ that are acting as miniature stress-risers in the grain structure of the weld. When you load that material in tension, teeny tiny little cracks start to form. When you load it in tension over and over again those cracks start to grow and, over time, cause the metal to weaken. That's something you can't simulate just by squishing stuff in a vise. The other issue is the way you are loading the material. Bending it along the tube wall isn't really representative of the loads an exhaust will see in service.

The way to test it, imho, would be to have a piece of 1" solid bar, bored out at one end to match your tubing and welded to a ~12" length of the stuff. Clamp the solid end in a vise and have an electric motor with an eccentric weight at the end of the tube to provide a fully reversing load. Then run the motor and see how long it takes for the weld to break. Repeat the test at least once with a different load... maybe just cut away the broken stuff and HAZ, the reweld and test at a shorter length. Load vs. Fatigue Life should be a straight line on a log-log plot.

Failing that, the best thing you can do to prevent fatigue failure is use a flex section. Basically, give the tubing room to move so that you minimize stresses due to expansion and contraction.

[Maxim]

Dual semi-truck stacks FTW! Just rip out those little fake vents in front of the windows and pipe them straight up!

[Dimman]

Originally Posted by old greg

Thanks for the shout out.

It's "Ah-Crop-Uh-Vich" btw.

Anyway, your test isn't really applicable to fatigue life for a couple of reasons. The big one is that fatigue strength @ half of a cycle is always going to be the same as ultimate tensile strength. The issue you are actually worrying about is that there are little bits of titanium oxide/nitride etc. in the filler and HAZ that are acting as miniature stress-risers in the grain structure of the weld. When you load that material in tension, teeny tiny little cracks start to form. When you load it in tension over and over again those cracks start to grow and, over time, cause the metal to weaken. That's something you can't simulate just by squishing stuff in a vise. The other issue is the way you are loading the material. Bending it along the tube wall isn't really representative of the loads an exhaust will see in service.

The way to test it, imho, would be to have a piece of 1" solid bar, bored out at one end to match your tubing and welded to a ~12" length of the stuff. Clamp the solid end in a vise and have an electric motor with an eccentric weight at the end of the tube to provide a fully reversing load. Then run the motor and see how long it takes for the weld to break. Repeat the test at least once with a different load... maybe just cut away the broken stuff and HAZ, the reweld and test at a shorter length. Load vs. Fatigue Life should be a straight line on a log-log plot.

Failing that, the best thing you can do to prevent fatigue failure is use a flex section. Basically, give the tubing room to move so that you minimize stresses due to expansion and contraction.

The weight used would be proportional to the intended weight of the exhaust? The loading that it's subject to is basically itself moving around from inertial and vibration, right?

We're also hoping that slip-fitting it will reduce some of the expansion issues.

Originally Posted by Homemade WRX

without watching the whole video, did he ever comment on what grade he was using? I'm guessing Gr5...really common and does well with heat.

That's part of the problem. It's mystery titanium. ('He' is me, btw...) I'm not sure if it's Commercially Pure or 6 Al 4V (Gr5?) or what. Apparently it was scrap from a company that does fancy heat exchangers. On Burns' website it sounds like CP2 is what they use. I'm still trying to sort out all the different terminology for the grades, as it doesn't seem to be as universal as aluminum or SAE steel yet. Some are the 'Grade' as you mention, some refer to the alloy, 6-4 for example, aircraft stuff has Alpha, Beta, and whatever the C stands for, with a minimum yield number, C100 for example.

Also for Serialk1llr, aluminum exhaust stuff on Burns' site:

http://www.burnsstainless.com/yieldstrength.aspx