Guest 73TPIZ Posted January 11, 2004 Share Posted January 11, 2004 This may be a stupid question but hear me out. Why can't you do an exhaust from aluminum tubing once you're 3-4 feet from the engine. Some points i'd like to list and see if there is a flaw in my thinking. 1. aluminum's melting point (per website) is 660 C which is ~1220 F deg. 2. looking at egt's on the net, didn't see many above 1400F and most at 800-1000Fdeg and this is probably near the header. 3. O2 sensors say if you're putting it in more than a couple of feet from engine you may want to use heated sensor as they only read above 600F deg. that tells me anything past a couple of feet must cool off fast. 4. you could run the down pipe and first elbow from steel and then connect to aluminum with a band clamp with a little seperation to avoid the corrosion. 5. is aluminized pipe actually aluminum coated. if so, why doesn't it melt? Also, why can heads and pistons be of alum and not melt. i know you have water circulating the head and oil splashing under the piston, but the exhaust port on the head must get hotter than the exhaust 3 feet from the engine does. this would save 20-40 lbs on some systems if it would work. I'm sure this has been discussed before but i didn't find anything on the net with a search. Thanks for any feedback fellas. Quote Link to comment Share on other sites More sharing options...
auxilary Posted January 19, 2004 Share Posted January 19, 2004 cost, difficulty to weld, and brittleness if overheated by welder would be my guesses. plus, some applications would easily get near the melting point (rotary runs about 1300* F at the exhaust ports) Quote Link to comment Share on other sites More sharing options...
Sparky Posted January 19, 2004 Share Posted January 19, 2004 what about just alum. from the "cat back" maybe a couple feet after the down pipe? it is spendy though, alum. mandrel bends run in the mega $$ range compared to steal or even SS. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 19, 2004 Share Posted January 19, 2004 The weight and price difference between thin wall stainless and thicker wall aluminum is minimal. I'm sure its been done but you don't gain any benefit and you add in one mechanical connection that adds to the price of the complete exhaust. Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted January 19, 2004 Share Posted January 19, 2004 Another thing is that aluminum work hardens pretty fast and then cracks easily. Exhaust systems heat up and cool down, thermal expantion and contraction, and they vibrate all the time. I would think that to counter that you would need to go with a relatively thick wall. Do that and thin wall stainless looks really good, like John says. Quote Link to comment Share on other sites More sharing options...
Guest 73TPIZ Posted January 20, 2004 Share Posted January 20, 2004 Thanks for the replies i'm wasn't aware of the brittleness factor. Yea, lots of thermal contraction and expansion. Jegs has the band clamps in the $10 ea range and i see some alum pipe and bends on ebay from time to time that compare pricewise to SS bends and pipe in catalogs, so i was just thinking out loud. Built my last sys out of aluminized pipe which held up well and plain steel mandrel bends that are rusting like a SOB. just looking at other materials for this sys. How thin can i get SS bends and pipe (.055" etc) and where is a good source. Also, do you just buy SS wire and run the same argon/CO2 mix on the welder? i'll practice with the SS on my stepson's prelude and then do a system on the Z. thanks again. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 20, 2004 Share Posted January 20, 2004 SPD in Sacramento (916) 635-8108 has 304, 321, and 347 stainless straight tube and bends in .035, .049, and .063 wall thickness. Tubing ODs from 1.250" to 5" and their mandrel bends can be had down to the tube OD (ie: 3" tube mandrel bent on a 3" radius). They aren't the cheapest but their quality is great and they provide great service. You'll need 308L, 309L, or 347 wire to weld 304 and 347 wire to weld 321 and 347. A C25 mix (75Ar 25C) works OK for stainless but there are better mixtures if you're doing a lot of stainless MIG work. Quote Link to comment Share on other sites More sharing options...
Guest Jason Posted February 6, 2004 Share Posted February 6, 2004 Besides the above reasons, Aluminum would also lose strength quickly as it got hot. I wouldn't recommend it. I bought stainless wire (308L and 309L) and expensive tri-mix gas for my MIG to try fabricating stainless parts. I never got the welder to put down beads like it did for mild steel. Frustrated, I bought myself a used TIG and taught myself to use it in less time than I wasted fooling around with the MIG. I recommend going this route if you're serious about Stainless, Aluminum, or some exotic metal. Plus, welders have good resale value, so look at it as an investment. I paid $700 for mine complete with Argon tank and water cooling system, and I couldn't be happier. -Jason Quote Link to comment Share on other sites More sharing options...
Guest 73TPIZ Posted February 6, 2004 Share Posted February 6, 2004 Jason, i've been wanting a TIG for awhile, i just can't afford it now. between solid rear end, subtle Z hood, and the SDS group buy, i'm surprized i can still pay my light bill . What brand is yours? Did you buy yours new or used? i thought they started at $1k and went up. That could be my next big purchase if i find one in that price range. BTW. My 2-8ft sections of 2.5" stainless tubing arrived today. Shame they go under the car! if i can't weld them nice, maybe i can tack them enough to remove them and take them to a welding shop. thanks Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted February 6, 2004 Share Posted February 6, 2004 Keep in mind too that the temp you are referring to is the melting point. That is the point at which it can become a liquid. Temperatures lower than that can have a serious effect on the solid. Think about what happens if you take a stick of wax and hold it over a flame. It will bend and lose it's form long before it gets hot enough to turn into a puddle. Quote Link to comment Share on other sites More sharing options...
Guest Jason Posted February 7, 2004 Share Posted February 7, 2004 I bought a used Hobart tig that was probably made in the mid 80's (back when Hobart still made industrial machines). Its a monster at about 600lbs and 450A output. I got lucky and found the welder advertised in the local classifieds, and even got it delivered for free. There were also some great deals on Ebay. It just takes some patience to find one in your area. I think the minimum price of a new Tig setup is about $1300. You can find some great DC only inverter based welders for slightly less, but these do not have high frequency, so starting the arc will be more difficult and unstable at low currents. HF is helpful if you're learning. Also make sure to get a foot pedal -some budget setups do not include one. New high end machines have various AC waveforms/balance that will probably do a better job at Aluminum, but I don't think manufacturers have improved much on welding steel over the last 50 years. All things considered, a new machine was just too much money for what I wanted. Used machines also depreciate more slowly, so I figured I could get most of what I paid by reselling the machine in the future, or perhaps by selling some stainless headers. -Jason Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted February 18, 2004 Share Posted February 18, 2004 don,t forget that the exhaust mixed with water vapor forms a very mild acid, aluminum gets eaten fairly fast in an acid enviorment, iron and stailess steel are effected far slower Quote Link to comment Share on other sites More sharing options...
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