Can a Aluminum downpipe be used on a RX7??????????????????
10-01-08, 08:01 PM
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Can a Aluminum downpipe be used on a RX7??????????????????
I've got a 5 inch downpipe, but the thing is heavy as hell. Can a Aluminum downpipe withstand the heat of a rotary?
10-01-08, 08:07 PM
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no, the aluminum wont last
whats the wall thickness of ur dp? i bought sections of 5" from a truck supplier, 16g aluminized steel.. see how long it holds up
whats the wall thickness of ur dp? i bought sections of 5" from a truck supplier, 16g aluminized steel.. see how long it holds up
10-01-08, 08:09 PM
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Mine is 16 gauge as well.
Just thinking, alot of the turbo mustang guys run them without problems. Just thought it might be a possibility for us.
Just thinking, alot of the turbo mustang guys run them without problems. Just thought it might be a possibility for us.
10-01-08, 09:19 PM
#6
I'm going to be running aluminum exhaust, but a stainless downpipe. I don't think the aluminum would stand much of a chance at the first bend after the turbine. Lots of heat and vibration Hell, the aluminum exhaust will probably crack out after a couple thousand miles, but we'll see.
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10-02-08, 06:41 AM
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not a chance.
egts w 100% alcohol run at least 1550 and while they lose some heat thru the turbine and aluminum melts at 1200....
the primary point is even if the DP doesn't see 1200 if it is close to that temp the aluminum will have no strength. add to it the major bend and you might be picking up puddled aluminum from under the dyno.
hc
egts w 100% alcohol run at least 1550 and while they lose some heat thru the turbine and aluminum melts at 1200....
the primary point is even if the DP doesn't see 1200 if it is close to that temp the aluminum will have no strength. add to it the major bend and you might be picking up puddled aluminum from under the dyno.
hc
10-02-08, 10:03 AM
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Titanium melts around ~1650 F, that's cutting it a little close for comfort if you ask me. It'd probably work, just big $$$. I'm all for someone that's not me paying to figure it out. 
10-02-08, 10:47 AM
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Your average grade of Titanium will not be stronger than 304SS, but will have a higher strength to weight ratio. Titanium also does not melt until 3000F depending on alloy, but will lose strength and corrosion resistance quickly as the temperature goes up. Also, good luck finding a long enough piece of straight 5" titanium tubing for $500 or less, let alone bends.
Thin wall (20 guage) 321SS or Inconel would be your best bet.
Thin wall (20 guage) 321SS or Inconel would be your best bet.
10-04-08, 02:45 PM
#19
Yep, they use inconel for high end exhausts because they can make it really thin/light and it will survive.
Inconel and stainless are less thermally conductive than titanium so you lose less exhaust energy/velocity.
Easier to weld too.
Inconel melts at a pretty high temp, but even better it creates its own protective layer at high temps.
As pointed out, titanium gets significantly weaker at higher temperatures so it would have to be thicker tube.
Nickel and steel
Good cast iron exhaust castings are also made of high nickel cast iron (Ni-Resist). Well, Ti is pretty kick *** for exhaust castings for weight savings as some lucky Evo owners know...
Inconel and stainless are less thermally conductive than titanium so you lose less exhaust energy/velocity.
Easier to weld too.
Inconel melts at a pretty high temp, but even better it creates its own protective layer at high temps.
As pointed out, titanium gets significantly weaker at higher temperatures so it would have to be thicker tube.
Nickel and steel
Good cast iron exhaust castings are also made of high nickel cast iron (Ni-Resist). Well, Ti is pretty kick *** for exhaust castings for weight savings
as some lucky Evo owners know...
?
10-11-08, 06:19 PM
#25
IIRC aluminum is good up to 370F, then it becomes soft like lead and loses its alloy properties, making it rather soft and weak. Exhaust temps are at least 1000F. Or it might get even hotter and melt like someone said. My point is even if you could get the temps down it'd still be a bad idea. I think steel has the same problem above 800F but heat won't screw up the alloy on mild steel. Unless you make your exhaust out of chrome-moly or some fancy steel alloy.
Ceramic does not block heat. It's snake-oil. It's not that it isn't an okay material, it's that a thin coating of anything simply cannot insulate. You need a thick mat. Likewise the thermal conductivity of other materials is entirely moot: your exhaust will be almost exactly the same temp on the inner wall as the outer wall due to the huge area to thickness ratio. The main barrier to heat leaving the exhaust is air.
Inconel would work well b/c it's a super high temp material; I doubt it'd even soften like steel does. That's fancy aerospace stuff there. Also costs a fortune. Titanium both melts and softens at a higher point than steel, so while it softens at high temps I would think that steel softens just as much or more. A quick google confirmed its use in exhausts. It's expensive though.
Ceramic does not block heat. It's snake-oil. It's not that it isn't an okay material, it's that a thin coating of anything simply cannot insulate. You need a thick mat. Likewise the thermal conductivity of other materials is entirely moot: your exhaust will be almost exactly the same temp on the inner wall as the outer wall due to the huge area to thickness ratio. The main barrier to heat leaving the exhaust is air.
Inconel would work well b/c it's a super high temp material; I doubt it'd even soften like steel does. That's fancy aerospace stuff there. Also costs a fortune. Titanium both melts and softens at a higher point than steel, so while it softens at high temps I would think that steel softens just as much or more. A quick google confirmed its use in exhausts. It's expensive though.
Last edited by ericgrau; 10-11-08 at 06:47 PM.