Is there any reason why an exhaust manifold couldn't be made out of aluminum? I'm not aware of any (for any engine), but is that just because of cost, or is there some technical/functional reason why it's not generally done? There've been aluminum heads and blocks, so it seems like heat resistance probably isn't the reason...there've been aluminum intakes, some of them quite large (Hyper Pak), so it seems like mechanical strength probably isn't the reason...

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan
The blocks and heads are water cooled. The exhaust would coke and then crack after the hot cold cycles.
I noticed the new modular engines are sheet iron instead of cast iron.
My02.
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

The heat..........

I'm not sure of the temp, but aluminum loses strength at a relatively low temperature (which it would obtain from the exhaust).

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Another problem is the larger thermal expansion coefficient of aluminum vs. steel/iron. This, coupled with the lower fatigue strength of aluminum probably makes an exh man more crack prone. Thermal cycling is probably worse too.

Lou

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Home of Slant6-powered fun machines since 1988

All of the above.

Note the temperature differences in this thermal image:



This ONLY shows external IR energy in the 8-14 micron range, converted to a false image, etc, technobabble blah blah blah. White is the hottest, fading into red where it gets cooler, blue is cool, black is coldest. In this image, the engine had been idling for a good while (180F thermostat, IIRC). The high temperature, on the exhaust manifold between 2 and 5, is 208.2C. The lower part of the intake, where it connects to the exhaust, is about 113C. At the end of the runners, the intake is about 76.3C. The head and block are running 80-100C. Interior temps would no doubt be higher on the exhaust

Detroit Wonder Metal (cast iron) can take higher temperatures longer than aluminum can, as already stated. The intake sees significantly less heat than the exhaust. Aluminum blocks use iron liners, exotic coatings, and/or carefully designed coolant flow to carry the heat away from the cylinders.

I'll have to figure out how to get some temperature data displayed here - it's embedded in the original image, but uses proprietary software to display. If I can post a .pdf or MS Word document, that'd work.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Pontiac 421 Super Duty's had aluminum exhaust manifolds in their Catalina drag cars. I read they left drops if aluminum on the track after runs down the drag strip.

Thanks for chiming in, I was hoping you would.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I've had (emergency circumstances) occasion to run an exhaust manifold on a stocker well into cherry red, likely well past aluminum's capabilities.
Perhaps the "overkill factor" in production engineering limits aluminum.

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Sex, drags, and rock & roll.
Dick, 225% crazy.
Hobby (cars, that is) Photos link

I had talked to Doc about that a while back about Aluminum Dutra Duals... his explaination was pretty sound... if you do timing or carb tuning and you get a lean out, the exhaust gas temps can be anywhere from 1100-1400 degrees depending, and that could make things a bit difficult for the aluminum to stay alive getting blowtorched like that...

-D.Idiot

The bottom of my intake gets exhaust heat..........

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Yeah....Im the one who destroyed this rare, vintage automobile.....

True, and the other side gets fresh air with a cooling mist.

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Sex, drags, and rock & roll.
Dick, 225% crazy.
Hobby (cars, that is) Photos link

And they're still known to crack.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

My apologies, I assumed the conclusion (I often neglect to spell it all out): That much temp dif's a big piece of the cause, thus the cracks would tend to validate the point being made.

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Sex, drags, and rock & roll.
Dick, 225% crazy.
Hobby (cars, that is) Photos link

Even 350 degrees can damage the heat treat of common 356 t6 aluminum.

Dan, what we really need are titanium headers. Nice thick walls, flanges drilled for their own studs above and below the ports, nice and long. Light as aluminum and more heat resistance than steel, no need for coating since they will never corrode.

I may be able to put a group buy together for as little as $10,000 a set.


Or how about Investment cast stainless Dutra Duals? They could come in at about a third of the mass of iron.