How easy is it to crack aluminum heads from over-heating?

[lemming303]

What temperature does it usually happen at? Does a higher horsepower engine make it easier to crack under heat? I would think that higher engine stress would make it easier, but I don't know a whole lot yet.

[quagmire]

Aluminum heads will warp long before they crack from heat.  Cast iron heads are much more prone to cracking.  That said, aluminum heads in OE applications tend to be VERY sensitive to warping.  In fact, many production car engines will pop head gaskets and need the heads milled anytime they overheat.  There really isn't any set in stone temperature, too many variables there.  Only rule I of thumb I can give you is don't let it overheat, shut it off long before it gets to that point.  I can guarantee a tow will ALWAYS be cheaper.

[lemming303]

I'm building this car to be 90% strip, 10% street. A friend of mine told me not to use the aluminum heads because they crack easy. However, I definitely think I want to go with the aluminum heads for the weight difference and the higher compression. I plan on building this 340 as beefy as I can get it within a moderate price range.

[femtnmax]

I worked for a number of years as an ASE foreign car mechanic.  Quag is totally correct, the aluminum heads will warp EASILY when overheated, but no real cracking issues.  I have seen cracks between valve seat inserts on some heads with over 100,000 miles, thats about it.
My daily driver is a rice burner with over 280,000 miles on it.  The engine has never been overheated, and the head is NOT warped at all, still meets OEM flatness specs period.   
Keep the cooling system in good conditon.  Always a good fan belt, etc.  Snap on makes a thermometer that you stick in the radiator fill, tells you the true temp regardless of what the thermostat is doing.  Then you know if the thermostat is working properly. I've seen brand new thermostats that were bad.
Instead of avoiding aluminum, a couple quotes I believe in:   Only run cast iron heads if your racing class requires it.  Most of today's aluminum heads flow equal or better out of the box as fully ported older cast iron heads.
For me, going aluminum is a great weight savings off the front of the car.  2 heads plus intake manifold is 25+25+20 lbs = 70 lb.  Then put the battery in the trunk is 50 lb off the front and into the back = 100 lb effective weight transfer for a grand total of 170 pounds shifted to over the rear wheels.   Many Mopar super stockers used a large truck/ bus battery to put even more weight over the rear wheels.
Most aluminum heads have helicoil inserts in all the critical threaded holes, best check before you buy.  Plus aluminum is easy to weld if you need to fix something.  I just converted an Edel air gap RPM intake to accept a thermoquad carb.  Was relatively easy to weld/add material where it needed to be.  Try that with cast iron.
I'm putting aluminum heads on my 360, and I won't be looking back.

[lemming303]

Sounds good man. I'm still very new to all this so I always ask a lot of questions. Thanks for the help.