Why no Ally exhausts?

[Aikman666]

Apon having a wee chat with the old man tonight who is both a seasoned rider and engineer I was talking about riveting my end can back together and was a bit apprehensive about using Aluminium alloy rivets incase they just melt away; to which he replied they're good up to around 120 degrees C.

So in that case, why dont bike manufacturers make exhaust systems out of it? Surely if the head can take the heat (as they are cast ally) then the pipes could too? With the added advantage of corrosion resistance, being cheaper and quite a portion lighter too.

So why havent I ever heard of it being done?
Neither of us could think of the answer.
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[tatters]

[Aikman666]

Alot of the systems i see these days are Stainless steel systems. But still it may be more expensive, yet I've never seen it on the best of race bikes etc?
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[bagger]

im pretty sure down pipes get hotter than 120C ive seen pics of some glowing red

[Kwaks]

No benefits to Ally, only downsides.

Yes it is about half the weight of steel, but only about 1/3 as strong, so would end up weighing more to match the strength.

More corrosive than steel, so no advantages there.

Down pipes get too hot for ally, and the whole system is substancially weakened by the heat through the system not to mention the stresses caused through the expansion.

The 3 most viable options remain S/S, Carbon & Titanium.
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[Ariel Badger]

The Badger uses one of these..
https://cgi.ebay.co.uk/Alloy-Trials-Silencer-Pre-65-AJS-BSA-Ariel-Enfield-AMC_W0QQitemZ270249208421QQcmdZViewItem?hash=item270249208421&_trkparms=72%3A12%7C39%3A1%7C65%3A12&_trksid=p3286.c0.m14
and some Broughs used ali downpipes with cooling fins.
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[c_dug]

My DEP end cans are ally, can vouch for them being weak as ive already had to have one of them welded once so i wouldnt personally go for the whole system even if it were available.

c_dug
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[ms51ves3]

[Aikman666]

The rivets we were talking about are an aluminium alloy as I understand it, probably to be plyable enough to be riveted in the first place. Aluminiums melting point is around 660 degrees C.

Kwacker is quite right, while it is one third the weight of mild steel it is also one third the strength, but how strong does an exhaust system really have to be? Surely there cant be alot of strain on it.

But it does however give much better corrosion resistance than its mild steel and certain grades of stainless steel counterparts.

Hmm
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[Kickstart]

Hi

Aluminium alloy melting points are around 600 centigrade. Quite a lot lower than the easily attained exhaust gas temperature.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Ichy]

Aluminium melts at about 660c but goes soft way before then. Pure guess that exhaust gases are about 200-300c at the header.

Corrosion is going to be another problem, exhaust gases mixed with water form hydrochloric, Sulfuric, nitric, carbonic and other bad acid stuff.

Then you have stress, aluminium has a short fatigue life made worse by the heat expansion.

Someone is developing a titanium aluminium alloy to use with exhausts making them about 50% lighter but I don't think that is recommended for header pipes.

If I was to make a lightweight exhaust I'd go for thin gauge stainless, F1 teams used to use Inconel, no idea what they use now.
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[Ichy]

[Kickstart]

Hi

From a brief look around, exhaust gas temperature gauges are used on some microlight. The expected temperature was ~1250 centigrade (which is actually above the melting point of cast iron).

This is the gas temperatue at a point. Presume the temperature of the gas where it meets the exhaust walls is lower, and also that the exhaust gas is only at that temperature at a certain point in the combustion process.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Mr Nice Guy]

Something to think about, considering that little bundle of joy (heat) is less than 10 inches below your balls!!
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Suzuki GSX-R750K4 ~ Mivv GP

[sidey]

[Old man]

[map]

[Ichy]

[Mr Nice Guy]

[Ichy]

[Pete.]

I've had ally end-cans before, no problem apart from how easy they are to damage.

Typical exhaust gas temps are 900-1100 deg C in the headers. The temps drop significantly as the exhaust travels down the pipes.

The reason ally heads don't melt under normal use is because heat is dissipated away too fast. It's what a cylinder head is designed to do after-all. It is possible to partially melt the head on a bike but not easy as the piston usually pops first.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ms51ves3]