Iron/Aluminum block?
 

Which is better for gas milage: Iron block(less hp lost due to friction), or aluminum block(Lightweight)?

My guess would be aluminum is better...

Tough to say. Aluminum will be lighter and less weight to push however, an iron block will retain more heat.

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.

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.

Just an FYI, all aluminum block engines have iron sleeves in the cylinders.

The exception is single cylinder consumer grade engines.

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.

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.)

You could always put insulation on the aluminum block. Make it retain heat damn well! :p

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.

As far as time to heat/cool an engine, here are the specific heats and densities of aluminum and iron:

Aluminum .91 J/(g*K)
Iron .46 J/(g*K)

Aluminum 1.00 g / cm^3
Iron 7.87 g / cm^3

Given design differences for the two materials, you'd really need actual engine masses for any sort of decent comparison. Since .91 / .46 = 1.978, you can say that unless the cast iron block is more than about twice as heavy as the aluminum then its thermal inertia would actually be less. In practice, what sort of weight differences are actually realized?

The biggest difference in construction material is at the cylinder head, not the block. The thermal conductivity of aluminum is much higher than cast iron, meaning less chance of hot spots and pre-ignition. So, an engine with an aluminum head can have a higher compression ratio. Hig compression = lower fuel consumption.

Many engines have an iron block and aluminum heads. High compression is the reason.

Yep. True

I don't think alluminum is hard enough. Hard metals to resist ware, light metals to hold the whole sytsem together.

As far as temperture regulation, it is your coolant system.
Your coolant only gets cooled IF your termastat diverts it to your radiator.
Every automotive I have ever drive uses temperture regulation to cool the engine, because any 4 stroke engine is a very effective heater.

Shell flex fuel, tried their new stuff, kinda liked the old mix.

Interesting thing I noticed is that a 6 cylinder Honda Accord Engine weighed much much less than a 4 Cylinder Toyota Corolla engine I had in 2000. Honda engines are all aluminum while Toyota at the time was using iron block, aluminum head engines. Both were mid nineties engines.

It also helps that Honda engines and trannies are so much smaller than Toyota engines/trannies.

That's why it's so easy to kill them.

Last I checked Hyundai is still using iron blocks in their 4 cylinder engines.

Check again. The Beta is still an iron block but the Theta is aluminum.

I say CI/CI or Al/Al/CIL - definitely not Al/CI

It's really hard to get a head gasket to seal with an Al/CI combo - not impossible mind you, just really challenging for 200K miles and beyond.

I like Honda because they have been making Al/Al/CIL for longer than most anyone else. The d-series SOHC VTEC engines with three layer metal head gaskets are among the most durable out there.

My Buick 3800 V6 is CI/CI and is OHV (push rods and cam in block). It's as old school as you can get but it works fine. The Buick has 154K miles and seems that it'll make it another 50K (fingers are crossed, though).

Most Kia 4 bangers are still Al/CI. I wanted to look at a 05 Spectra today but was turned off by the head/block combo and changed my mind.

Also, not really thrilled with composite(plastic) intake manifolds. Cast aluminum is much better. A buying requirement for me.

The Geo Metro uses an aluminum (cast-iron sleeves) engine. It is nice because I can actually pick up the engine (about 170 lbs). Can't carry it far, though. Haven't heard of any problems due to aluminum construction.

The Cad has an aluminum block (with cast-iron cylinder liners...think water-cooled Corvair) and a cast-iron head. Supposed to give a lot of problems, but I haven't had any. That was one way they could reduce the weight of the car, get decent power and mileage.

The old Vega with all-aluminum block (no sleeves) was pretty bad...wore out quickly. The real train-wreck, however, was the early Mazda rotary...aluminum rotor housings with steel end-caps and bolts. Run low on coolant one time, the rotor housing expanded and cracked. After that, rotor housings were toast. I know....I did that around '79 or '80.

GM pioneered the Nica-sil aluminum block in the 63 Oldsmobile F85. It was A V8 OF 215 cubic inches turbocharged with 215 horsepower and weighed 215 pounds.

That technology was licensed to Rover and used for many years in their 3.5 liter engines. It was also licensed to Mercedes and first used in their 380 SL which was a good engine when they abandoned the single row timing chain. Also adopted by Porsche in the 928 and 924 if memory serves me correctly.

Very hard surface of the cylinder walls but no possibility of boring the block for a rebuild.

I agree with the previous statement about using the same materials for block and head, becasue similar expansion characteristics make it much easier to keep the head gasket sealed for hundreds of thousands of miles.

regards
gary