I think I will be keeping my stock exhaust for a while if I change it at all. I have purchased a UT-R y-pipe but don't want to install it because I don't like the fact the the outlet diameter is larger than the inlet of the mid-pipe. I know turbulance will be generate which may not be a big deal but anyways......

I would like to have a custom y-pipe made with a 65 mm (approx. 2.5") outlet since an aftermarket version of this doesn't exist.

I have a few concerns I would like to discuss.

1. Are the flex hoses required? What is the reason they are provided? Is it so the whole system isn't so rigid? Could I purchase universal flex hoses? Maybe I could buy some cheap exhaust components and use the flex hoses.

2. Why isn't aluminum typically used for exhaust components? Cost? Strength? I was thinking of using 6061-T6 aluminum. I could probably get a custom circular tube extrusion with a 2.5" I.D. and a 1/8" wall thickness. This should provide adequate bending stiffness.

3. What kind of service temps can be expected? If they are too high I guess that would be the reason why aluminum isn't used. Anything less than 350 degrees F should not be a problem. If this is the kind of temps I am looking at I guess it could be powder coated without any problems.

The below existing design would be my starting point because it would be the easiest to fabricate and should provide smooth flow characteristics and good sound. I was even thinking of getting it dynoed. This would be nothing more than a fun project.

Please provide your thoughts!

 

A very good question. I also want some info. and feedback. I was considering having a custom y-pipe built with 2.5" piping. I have attached a picture of the 3" Japtrix Y-Pipe & mid pipe, which is being sold by a MY350Z.com member in Florida for $360 (y) / $300 (mid). The dyno results were reported to be 5-6 rwmph increase on the Y Pipe & 11 rwmph combined. It's a straight and simple design.

 

I'll take a stab at this one...

1. Yes and No. They are not mandatory but very desirable. If you ever hit anything like a speed bump, etc... it is nice to have the flexures so that you don't break part of your exhaust. Bolts can snap, pipes can dent or break or something even worse can happen. Also your engine moves when you depress the gas. The engine is attached directly to the headers (rigid connection) which is attached to your y-pipe (rigid connection). Ever see a car on a dyno? At WOT the engine moves a good bit, thus the reason why the Crawford h/f cats may or may not rattle on some cars.

2. Heat! The stock cats can get up to 600-800 degrees F. The y-pipe can easily see half of that temp after a good run or two. Also, steel is stronger than aluminum so in order to get the strength from the aluminum you need more of it. Look at Tensile Strength, CTE's and densities of the 2 materials. Thin walled steel (stainless preferrably) is a better material for corrosion, strength, heat, etc...

3. see #2.

Hope that helps.

 

Hey Neff,

How's it going. I just checked my fathers research and found that 6061-T6 Aluminum doesn't loss any strength until it is heated above 232 Degrees C. At this temp you would have 95% of the parent metal strength. The yield strength of this material is 35 ksi. About the same as A304 depending of your sources.

Parent metal strength is not the issue here. It's the lower temps. at which aluminum is annealed when compared to steel.

It was 2024-T4 Aluminum that retained 95% of the parent metal strength at a temp. of 350 degrees F. This alloy cannot be extruded so thats out.

So there goes my aluminum y-pipe idea.

I will try to determine the surface temp. of my oem y-pipe when I have time.

Neff, I will let you know the results of my experiments. Everytime someone tries to re-invent the wheel......

 

Long story short,

1) Aluminium's working temperature is lower than that of the exhaust temperature (especially the y-pipe or the cats).
2) The strength of Aluminium is far below that of Stainless steel

cheers,
Godmans

 

Both my father and I are structural engineers. My father has his Ph.D and is know to be an expert in all of Canada on the topic of welding aluminum. He has published a thesis and a dissertation on the topics of the heat effected zone adjacent to a weld specifically for aluminum. Trust me I know a thing or two about this stuff. Our company provides welding certification for over 20 companies and we design over 100 aluminum structures annually.

Yes I stated that the 95% of the parent metal strength exists after being subjected to 232 degrees celcius. This is for 6061-T6 of course. I have done endless amounts of experiments and testing to determine this. The only thing I didn't know was the operating/service temp. of the y-pipe. We have previosly concluded that it is above 232 degress celcius. I will verify this myself.

In regards to strength:

A304 Stainless Steel- fy=38 ksi or less
6061-T6 - fy=35 ksi
6351-T6 - fy=37 ksi
2024-T4 - fy=over 40 ksi(I can't remeber exacly)

So you see, some aluminum alloys have excellent strength properties. Any 6000 series aluminum alloy section can have an equivalent bending stiffness to a similar stainless steel section by simply providing a slighty larger section modulus.

Thanks for you input. I hope you learned something.

 

i started a thread a while back that helped out several members here regarding the y-pipe to b-pipe diameter differences. I had a flange & reducer cone fabricated that "gently" reduced the diameter over 4-6 inches. do a search for reducer or y-pipe that should bring up the thread. I think it was about 30 bucks.

 

I know that this is an old post but if you and your father are engineers it seems that you should know that 232c is 449.6F.

THe manufactures are installing all stainless exhausts on diesel truck engines which can reach temps of 1000F... go stainless