Titanium vs Steel: Weight, Exhaust Tubing

Discussion in 'Technical' started by dahldrin, Mar 23, 2006.

  1. Just wondering if anyone has weight numbers (preferrably by foot) for various titanium tubing. I'm trying to determine if the weight savings would be worth the price difference for the custom exhaust I'm making.
     
  2. #2 EliseS2, Mar 23, 2006
    Last edited by a moderator: Apr 25, 2016
    Just calculate it yourself using the density of the material.

    www.matweb.com
     
  3. I'm willing to bet that it isn't worth it, unless you have a really strict weight goal. It isn't going to save you enough weight to make it worth your while, plus, it'll be really expensive. Just go with steel.
     
  4. Matweb says Ti is about 58% the density of steel. If the entire exhaust were made of nothing but Ti, you'd cut 42% off, but you can't include the cat or muffler weights in that calculation.
     
  5. Titanium is also about twice as strong as most cold-rolled steels in tension - thus your tube diameter could be much thinner than steel, for a given hoop strength.

    Before you even make the choice, make sure to find a good place that can actually WELD the titanium - most shops don't do a good job at it. Titanium is one of the most difficult metals to weld properly without slag or nitrogen bubbles. The last thing you want is to have cracks in your exhaust joints.
     
  6. I always put crack in my joints as a matter of course.
     
  7. Do you have a frame yet or what?
     
  8. It's like, 75% complete. I'm waiting on the roll bar (having it bent at a local shop) amongst other things. The rear suspension hasn't been built yet as I'm still trying to decide which route to go with the axles. I'm likely going to have custom length axles made but it isn't going to be cheap and the turn-around time could be as long as seven weeks from when I give them the length.

    This question just popped into my mind so I figured I'd ask before I forget. I asked it in the way I did as I thought there may be a site specifically for this sort of thing. With like, tubing diameter, wall thickness, strength(s) and weight. I found a similar table for structural tubing, but nothing like I'm looking for (3" thinwall).

    Also, I'm not going to be running any mufflers or cats, so it'd all be tubing (and likely some SS tips, if possible with Ti anyway). It probably wouldn't be worth it as the whole exhaust is only going to be three to four feet of tubing, but I was just trying to sort of come up with a list of ways to save weight where ever I can.

    Thanks for the help.
     
  9. I dont knwo what to say but I know a lot of cars that you can buy FULL Ti exhaust weigh in around 9-11lbs.

    Thats all the piping too the canaster.
     
  10. if your going to have a little extra weight anywhere, it might as well be on the bottom of the car
     
  11. It's sort of the midsection of the car actually. It's midengined and the exhaust is going to exit about two feet off the ground between the taillights.
     
  12. a couple extra pounds over the drive wheels
    save a couple bucks
    besides, steel holds heat better
     
  13. That's pretty much the conclusion I've come to my self. Especially when I take the length of the exhaust into consideration. Also, you can't mandrel bend Ti, can you? Not having mandrel tubing would be a pretty big negative given the path the exhaust needs to take.
     
  14. I don't see why you couldn't manderal bend it
    but everything is going to be easier with steel
     
  15. The titanium will expand more than the steel too, so you'll have to take that into consideration with your exhaust hangers and how close other items are to the exhaust tubing.
     
  16. It depends on how extensive your exhaust system will be. If it's going to be a few mufflers and, say, 6 feet of piping, then yes it would save a considerable amount of weight and would be a great bragging point. However, if you're going to have a short, stubby exhaust system with, say, one muffler, it's not worth the time/money. Titanium is also a #%!@ to weld.
     
  17. For your situation I'd probably just go the cheap and easy route with steel for now. Since your basically building a car from scratch, you probably have more important things to worry about for now. Use steel to get the proper sizing (not sure where you are on your project, but there is chance you may have to re-adjust your exhaust dimensions for proper fitting as you install components.) Once, youve got the car running and exhaust dimensions figured out, get the Titanuim.
     
  18. Titanium oxidize at temperatures above 600 degC. Titanium is not suitable for exhaust manifolds due to this reason. Its high temperature strength is also not as good as a heat resistant stainless steel or a superalloy like inconel.

    For a low weight exhaust manifold I recommend the use of thin wall inconel tubing (just like in F1), it's not cheap or easy to manufacture but the end result is excellent. There are also a number of stainless steels that are suitable as exhaust manifolds.
     
  19. I guess I should've been more clear. I'm definitely not considering using Ti for my exhaust manifold. For that I'm simply using a ported stock manifold with a billet steel adapter (w/ ext WG). Regardless, I think I'm going to go with plain, old steel and have it ceramic coated or something.
     
  20. Note that most ceramic coatings that are sold for exhaust systems aren't real ceramic coatings like those you find in the aircraft industry. The latter ones are also quite sensitive and must be applied with a ground coat first on a metal such a superalloy. This ceramic is applied by plasma spray, EBPVD and so on.

    Mild steel is not suitable for exhaust manifolds at all.
     
  21. I was thinking I'd go with something like HPC's HiPerCoat Extreme. It's a 2000*F coating and is actually FAA certified.

    "On-track testing has shown as much as a 35% reduction in under hood ambient temperature and more than 50% reduction in component skin temperature."

    This is kind of interesting as well:

    "Independent testing of a turbocharged 4-cylinder engine has shown a 5% increase in horsepower when HiPerCoat Extreme was used on the exhaust manifold, turbo and downpipe."

    Again, all I'm talking about fabricating is the turbine outlet back. I'm not talking about fabricating a manifold, I already have that (as mentioned in the previous post). Though, I think I'll have the manifold, adapter, turbine housing and exhaust tubing HPC coated.
     
  22. #22 BLACKANGUS, Mar 26, 2006
    Last edited by a moderator: Apr 25, 2016
    Jet hot your manifold, racers use it all the time, they produce high quality coatings inside and out for a good price, your stuff comes back looking new too. Plus it keeps the heat in the headers for reduced underhood temps...so, more horsepower. That and it looks great.

    http://jet-hot.com/

    Just curious, what are you building? I haven't heard of many people running titanium exhaust, nor have I heard of people needing to shave weight as strict as worrying about exhaust weight. The cost involved with titanium exhaust and welding could be invested in lighter parts elsewhere. I and many others are happy with mandrel bent aluminized pipe or even stainless steel. Interesting idea with the Ti tubing though. Good luck with whatever you settle on.
     
  23. #23 SaabJohan, Mar 27, 2006
    Last edited by a moderator: Apr 25, 2016
    Coated manifolds do not increase horsepower. For protection against heat radiation I would also recommend the use of heat shields instead.

    The coatings mentioned are not "real" thermal barrier coatings. On the following link you can find the same type of coatings that are used by manufacturers of aircraft engines. These are typically yttria stabilised zirconia, ceria stabilised zirconia or magnesia stabilised zirconia on a bond coat of CoNiCrAlY or NiCrAlY. They can be applied using for example a plasma spray. Note that when used on exhaust manifolds only the inside is coated, just like with gas turbine burners. These coatings are also brittle, so they can easily be damaged. In a turbine application a coating like this can reduce blade temperature with say 50 degC.

    http://www.plasmacoat.co.uk/coatings.htm#thermal

    The so called coating that Jet Hot and similar sell is not a real ceramic coating but ceramic powder in a matrix similar to heat resistant paint, hence it's possible to apply these without the expensive equipment real TBC require. These can't offer the performance of a real TBC but they can protect non stanless steel from corrosion (for a while) and thereby create a better look.

    For isolation before a turbocharger, and isolation of turbine housings I recommend the use of heat insulating fibers (carbon, silicone oxide and similar) under a heat reflective film. This is used by for example Honeywell on some racing turbochargers such as TR30R.
     

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