Consider a Keith Black aluminum street HEMI block.
* They weigh only 140 lbs. A 572" KB HEMI weighs LESS than a 440. You don't even need to change the torsion bars.
* They can handle 2000 HP. Yes - they're stronger than an iron motor. The street HEMI KB block is a full water block, but still it's strong enough to handle severe racing applications.
* These are STREET blocks. In other words they carry water, work with almost any water head, cool great, can be configured for normal motor mounts, etc.
* The DON'T leak. The fear has always been that aluminum blocks leak water around the sleeves. Well, the new aluminum blocks DON'T LEAK! KB and INDY have spent a lot of time and R&D $ figuring out how to keep their blocks sealed, and they solved it years ago. It's a combination of design and assembly techniques but IT WORKS!
* They can be fixed. This is a minor point because you shouldn't be "fixing" a block, but aluminum is repairable, whereas cast iron is not.
* They are available, built to order, and require minimal machining once we get them.
* They look great.
* They are more expensive. But not as much as you might think when you consider that a $2300 (approx) Mopar block requires about $800 of machining before we can use it. So the actual price increase is about $3100. If you're spending $25K to $50K on you car (often A LOT more), and then another $17K or so for the HEMI engine, does the extra $2.5K really squelch the entire project?
* There is no provision for an internal oil pick so all oiling must be external. This is better anyway since stroker crankshafts always hit the internal pickups and external systems flow more oil. (Note the double main cap cross bolts in the picture.)
* The is one motor mount hole on the drivers side which had to be moved because of the superior oil galley that Keith Black casts in the block.
* There's another "con" we need to mention if your building an all out race motor. Everything else being equal, the aluminum motor will make a little less horsepower. As much as 20 HP, on the dyno, on 900 HP motors. This is because the engine is basically an air pump AND a heat engine, and it's harder to keep heat in an aluminum motor. Also, aluminum moves around more, so ring seal varies at very high cylinder pressures. But this only affects all out race motors. On a street motor it would be hard to measure any difference, and any slight decrease in HP would be more than offset by the decrease in weight.
But there are some good reasons to consider an iron block:
1) The KB blocks require external oil lines and the longer oil pump may require grinding the K-member. This can cause installation headaches if you have a car with a normal K-member, motor mounts, headers, etc. The KB blocks are designed for big stroke crankshafts which would not work with an internal oil pickup.
2) The external oil lines can interfere with street type headers. You may have to rerouted the oil lines after engine installation in the car.
3) There is no provision for a mechanical fuel pump (electric pumps are better anyway).
4) Aluminum expands more, so mechanical valve lash must be set hot. Hydraulic cam lifters need 1/2 turn more preload.
5) Bearing clearances are tighter on a cold engine, so aluminum motors must be heated up before high RPM operation.
So if you're okay with a smaller displacement HEMI, with a nominal 3.75 to 4.15 stroke, and with an internal oil pickup, then the iron block is fine.