first part:
my friend and i were talking and thought the only negative to steel is it transfers heat more efficiently. i want to build a proper exhaust and have as much aluminum in it as possible to keep weight at a minimal. to over come the transferring of the heat i was going to warp the full exhaust. i know im neglecting something large because ive heard of few aluminum exhaust. :help enlighten me

second part:
car reving to 7200 max what size would you guys recommend 2.5 or 3.

you might have issues with different expansion rates. eventually the aluminum would crack. it might not even last a year. the big money guys use titanium. it has good resiliance and it is also a thermal insulator. good for keeping the exhaust hot on the way out.

how about carbon fiber tubes?

Isn't the Kromer Kraft exhaust alum?

Vince

Isn't the Kromer Kraft exhaust alum?

Vince

No, they offer a coating like many other header mfgs. Aluminum has too low of a melting point to be used for headers.

odortiz: thanks and the expansion also crossed our minds but i left it out. guess it was a bigger factor that i original thought. i did think about titanium....got to get some paper first. ill continue to give this ltw exhaust thought.

i've read that welding titanium is hard to do. if the welds get contaminated with oxygen, they are as brittle as glass. i have no experience welding though.
good luck and post up what you make.

Welding AL isn't trivial either.

Welding AL isn't trivial either.

true. i consider welding an art form. i can join steel with a welder, but i wouldn't call it welding. if i want it to look nice, i give it to somebody who knows what to do.

You need one of these:

http://www.turnermotorsport.com/image/Intake_Exhaust/remus_e36_titanium_lg.jpg

Aluminum loses half its strength at 300 degrees and keeps right on downhill from there. In an exhaust it would sag like wet cardboard as soon as it got hot.

Neil

Aluminum loses half its strength at 300 degrees and keeps right on downhill from there. In an exhaust it would sag like wet cardboard as soon as it got hot.

Neil

alum. is too soft, expands too much and has a low melting point......no good for exhaust tubing.
.......perfectly okay for a mufflers since it father away from heat source! Thousand of motorcyles
have aluminium mufflers...

welding titamium requires "back gassing" as TI needs to be completely shielded from oxygen
while cooling including the backside of the weld.....

more info....

Titanium is a reactive metal that forms compounds with less than optimum properties.
Heated in air, the part surface contains brittle carbides, nitrides, and oxides, each of which can
reduce the fatigue resistance and notch toughness of the weld and heat-affected zone (HAZ).
Not only do you need to protect the surface being welded, you also need to protect the back
side of the weld, which is just as sensitive.

This is why in many factories titanium welding is done in "glove boxes" in a complete inert environment.

here are a few examples of "glove boxes"

http://www.precision-weld.com/images/BubbleWelding-006F-200.jpg
http://www.spar-tec.com/large/1158_welding_chamber_cyl_l.jpghttp://www.myfen.com.au/Uploads/PressReleases/fen/Images-20071003/latestnews.jpg

If no "glove box" is available then you have to get a separate Argon tank and setup a proper
back-gassing. This takes some time as you need to figure out a way to close the end of the
tubes your welding and put a hose thru it etc.....etc....

here is a pic of a fabricator making a ti ducati rear subframe. Please note the tube of Argon
piped into the tubes and the tape over all the open tube ends....thus purging the inside of the
tubing of oxygen. Kinda replicates the inert environment of a glove box setup.

http://www.arcfabrication.com/images/DSC000039.JPG



Chlorine from the perspiration on your hands can create localized corrosion. “White-glove” treatments
are not just a sign of quality in welding titanium; using lint-free gloves after the final cleaning before
welding may be necessary for the highest-quality welds.

Any time the metal reaches a temperature of 900 to 1,000 degrees F, brittle oxygen-stabilized alpha
phase (or α-case ) can form not only on the weld surface and its back side.

for best Success.... High-purity argon; clean work areas free of combustible grinding debris; the
white-glove treatment after thorough cleaning; well-designed and -maintained purges on both
sides of the part to distribute the argon evenly; and the technique of holding the torch in place
until the metal has cooled below 500 degrees F should produce a clean, silver-colored titanium
weld every time.


In sum, welding TI takes more care and preparation which usually = more money.
Unless your doing it yourself.

A proper TI weld will be shiny silver....almost like mercury. The traditional "rainbow" color
pattern occurs when TI is heated and oxygen is present. which is why you might see it a
few milimeters from the bead.

If the bead is rainbow colored you have problems!

here a nice shiny Ti weld.

http://bobswelding.tripod.com/DSCN1046small.jpg

You need one of these:

http://www.turnermotorsport.com/image/Intake_Exhaust/remus_e36_titanium_lg.jpg

I have no idea the specs on that exhaust, that looks like a regular old STEEL muffler with riveted on TI exhaust tips. You can clearly see the rivets in this picture. Nothing special about the above exhaust....

in any case

There are a few complete Ti exhausts out there for the e46 M3.....pretty damn pricy if I remember.....never seen one for the e36 M3

thanks for your contribution....looks like ill shed weight else where.

Honda's have used 3 - 4" aluminum exhausts for a while now. That's on a turbocharged car that sees higher EGT's. Some of these cars are up in the 700 - 800whp range.

Might head over to Honda-Tech and see if anyone has had longevity issues.

you might have issues with different expansion rates. eventually the aluminum would crack. it might not even last a year. the big money guys use titanium. it has good resiliance and it is also a thermal insulator. good for keeping the exhaust hot on the way out.

how about carbon fiber tubes?

The big money guys use Iconel now.

You can get very thin walled steel tubing that is up the the task. If weight is a big concern, make the system shorter and have it exit from the rocker panel.