Aluminum vs. Iron FE block longevity

tirod · #1 (**permalink**) 06-11-2012, 09:33 AM

The OEM use of aluminum in blocks is pretty much the long term solution for them. It's cheaper to cast, cheaper to machine, and they get engineering and gas mileage out of it.

One area that is more problematic with aluminum blocks - overheating. If you let them get hot - really hot - the torqued bolts will pull the threads in the block. You can rebuild them to your hearts content, they won't hold the threads after that, and they are junk. It's a significant issue for street cars these days - they get new head gaskets but they won't hold.

Used aluminum heads and blocks from the competition scene are on the market for a reason, too - if they were any good, the team would recondition and reuse them.

Iron won't do that, it'll crack, as the thread on F4TE 351W's relates on TOS. If you look for it, you find it. Most of us can't find soft aluminum in threaded holes.

If you want to run aluminum and enjoy it's many benefits, you need to take more precautions with the cooling system, and it wouldn't hurt to be paranoid about overheating. Aluminum blocks make expensive man cave tables.

There's a another trend that just hit visibility, the use of compacted graphite iron blocks. These are supposed to offer a lot of advantages, and may become a big player. Remains to be seen, but there are folks casting and running them. If World or others offered them in the next five years, it would be nice, I'm not planning on it.

The roadster has a rear weight bias already, the 150 pound difference off the front is likely less significant than a good set of ported heads, brakes, or six speed. In a car already pushing 6.5 pounds per hp, overall handling won't be as affected by an aluminum block alone - the money could get you a lot further in other areas. It's a matter of balancing the design and spending money where it gets the most bang for the buck.

If it was a choice of aluminum block with carburetor and donor brakes, vs iron block, tuned EFI, six speed, and big rotors with 6 piston calipers, it wouldn't be a choice. I'd run an iron block.

What you'd likely get with an aluminum block are all the other goodies - and 650 hp, but that can be done to iron, too. Aluminum doesn't bring that much to the table all by itself, it's just one part of the overall recipe to a performance level.

Dominik · #2 (**permalink**) 06-11-2012, 10:25 AM

Good day!

I don't want to sound clever, but the 150lbs weight savings will not affect your daily driving, unless you do some serious racing.

I love weight savings as much as the next guy - probably more (1950lbs in the 90s with a 496cui alu Chev), but the cost doesn't justify it.

There is one bonus: Aluminium cools better.

Also, you would be surprised where you can save 150lbs on your car. Start with rotating parts which give you a higher "return of weight savings" and then reduce your unsprung weight.

Thirdly: how much do you weigh ;-)