Iron/Aluminum block? - Fuelly Forums

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Old 03-27-2009, 05:35 PM   #1
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Iron/Aluminum block?

Which is better for gas milage: Iron block(less hp lost due to friction), or aluminum block(Lightweight)?
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Old 03-27-2009, 06:30 PM   #2
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My guess would be aluminum is better...
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Old 03-27-2009, 07:14 PM   #3
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Tough to say. Aluminum will be lighter and less weight to push however, an iron block will retain more heat.
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Old 03-27-2009, 08:46 PM   #4
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Not as straightforward as it might first appear.

The alloy block will weigh somewhat less but not a lot since more is needed to give the necessary strength and thin wall cast iron techniques can mean an iron block for a very similar weight.

The iron block will retain heat for longer but then again the alloy block will reach it's operating temp more quickly.

As a quick and dirty guess I would vote for the alloy.

Pete.
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Old 03-27-2009, 08:51 PM   #5
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Oh yeah...almost forgot... the friction component is essentially the same in both engines if they are using shell bearings and these days most do.

Detail design can make a significant difference beyond the base materials used for the casting...tapered intake runners...drilled cam shafts to save weight...variable valve timing etc etc.

Cheers , Pete.
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Old 03-27-2009, 09:21 PM   #6
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Just an FYI, all aluminum block engines have iron sleeves in the cylinders.

The exception is single cylinder consumer grade engines.
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Old 03-28-2009, 03:59 AM   #7
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I wasn't aware that there were friction differences. Do cast iron sleeves entirely remove that effect, or is there much friction elsewhere?

There are far too many variables. We would have to take a specific case with well-known properties. How much weight will be lost, how much does the vehicle weigh as a whole, how does power production differ between the two engines, just how much friction loss are we talking about, what type of driving, what is the car's cD, etc.

Simply reducing the weight by 50 pounds or whatever you get out of it is really not going to be effective, except in specific cars that are sensitive to weight loss or in specific cases of aggressive 100% stop-and-go driving. There's a link in my sig to a discussion where people report which cars are and are not sensitive to weight loss. Throw 200 pounds of crap in a Buick Lesabre on a 3000 mile highway trip and you'll never measure a difference; throw the same 200 pounds in a 1992 Civic DX in 500 miles of downtown NYC driving and you'll measure a big difference.
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Old 03-28-2009, 05:16 AM   #8
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I'd probably say with the swifter heating of Aluminum, and the heat retention of Iron...

Aluminum block is better for city, iron for long trips. (Don't need to re-warm up after that stop at the restaurant.)
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Old 03-28-2009, 05:17 AM   #9
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You could always put insulation on the aluminum block. Make it retain heat damn well!
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Old 03-28-2009, 05:51 AM   #10
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The Tracker had an aluminum block and aluminum head and the Durango has iron block and iron heads. They both end up at about the same temp by the time I hit the freeway in the mornings. I haven't noticed that one car cools faster than the other.

Even with an all aluminum engine you are looking at a 60-40 split of weight in a front wheel drive car so reducing the weight of that engine up front means a lot.

As for friction, everywhere the crank, pistons touch are the same as in an iron block engine. The cylinder sleeves and main bearings assure that.
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