belz

For racing purposes ...
What material would offer the best combination of weight reduction and longevity on a turbocharged car (i.e. 951)?
I like the idea of "jet-hot" coating ... so would 3" aluminum "JH - coated" pipe work - would it last? Stainless best? Thin walled mild steel? Unatainium?

Danno

Nah, no go on the aluminum, it'll probably melt. What you want is strength-to-weight. Aluminum as 1/3rd the density of steel, but 1/3rd the modulus of elasticity. So any given sample of the same strength would weigh the same.

Aftermarket stainless systems would be a little better than stock because they use thinner wall tubing and leave out extra stuff like catalytic converters. The 321 stainless is more desirable in heat-intensive environments than the usual 304 stuff.

Best would be titanium. Some alloys like the 6va/4al stuff easily has 2x the strength of steel. So you can design an exhaust that has the same strength as stock but weighs 1/2 the weight. Check out the titanium exhaust on the Z06.

And yes, unobtanium would be best. Zero weight, infinite strength and no need to coat with special coatings to resist heat!

belz

Thanks Danno ... now where can I find some unobtainium?!

Is there even a source for 3" titanium pipe!? And how expensive would that be!?

Dave

If you have to ask...

Thaddeus

Just out of curiousity, how does one weld titanium? It's my understanding the stuff is toxic, not something you want to be inhaling...

Thaddeus

marksportcts

You would possibly be welding with some sort of gas mask under the welding mask. Try Burns Stainless www.burnsstainless.com

belz

Thanks for the link ... I didn't see 3" titanium ... I'll call them.
The webpage did mention that titanium is not suitable for high heat applications such as turbocharging .... hmmmmm?
I wonder if you used a stainless downpipe if you could then use titanium the rest of the way? Trying to save ounces here!!!

Skip

Either B&B or Borla had a display at the SEMA show this year in which they were showing off the new Titanium series of mufflers and pipes. Since both of these companies have Cat-back systems for your car, there's a good chance they may have what you need. But, like Dave says, "if you have to ask..."

Also, as far as I know... only travelling caravans of gypsies have the *unobtanium* you seek. They are not due in your neighborhood for another 5.1 dog years.

Skip

marksportcts

I think they mean that it shouldn't be used for the downpipe as it will be the hotest part of the exhaust after the turbo. You could use titanium for the cat-back if they have it large enough.

Manning

I think titanium is listed as unsuitable for a turbo app on the site is because it tends to flash like magnesium when it gets hot. I haven't check out the site yet.

Regarding welding, it requires a purge gas like argon so that the weld does not get contaminated by O2. It is weldable as made evident by many welded titanium bicycle frames on the road and trails today.

Steve Lavigne

I think the closest you can get to unobtainium is inconel. This is what F1 teams use. It is very thin, and thus light. It also can stay stable at very high temperatures and insulates against heat very well. I imagine that the F1 teams probably break out a new set for every race, so the long term durability would definitely be a problem.

How fast do you want to go? Heh

Danno

Yeah, titanium is probably not good for stuff around the turbo because of the high heat. While very stable at any temperature (it doesn't rust, corrode, burn), it does have a lower melting point than steel. The titanium skin on the SR-71 Blackburn would glow red-hot at supersonic speeds (mach 3+) and actually melts and flows to the back of the wings!

Although I did get a titanium exhaust system for my VFR over a decade ago. It came in a box of 17 individual sections and the only insructions were on a 3x5" index-card that said, "Cut & weld as necessary."

The titanium-based 321 stainless alloy is probably best for exhaust headers and turbo down-pipes. It doesn't have the embrittlement problem that 304 stainless has at high heat.

Welding titanium is similar to stainless. You use a 100% argon shielding gas. Important part comes down to preparation. Ideally you want to back-fill the part and weld in a 100% atmosphere (welding room with respirator). The fact that a lot of the stainless exhaust parts aren't welded like that leads me to suspect a lot of it.

Speaking of Inconel, there's a couple of HKS & IHI turbos that have Inconel turbine blades. Combined with ceramic compressors, these things should be pretty wicked.