What's the real deal with aluminum blocks? Obviously they save weight but is it true the combustion isn't as good as in an iron block? I was going to go with an aluminum block, but I just can't seem to justify the cost of one. Right now, I'm leaning towards the rocket block (thanks for the tip Qwktrip) from SDPC with the 4.125" bore that way I can buy a custom crank and make that 427 small block I've always wanted. The main goal that I want for the car is to handle really well and be streetable. It'll be my weekend fun car. So which would be better for my application, Fe or Al? Thanks.

 

The Al block will have Fe cylinder liners. The lower performance from aluminum relates to heads, where the heat transfer characteristics of aluminum reduces power produced.

 

why would aluminum heads make less power??

 

Did I do that? That must have been ages ago because I can't remember! LOL

Tas, if you put two heads side by side that are identical except one is iron and the other is aluminum, the iron head will make more power. This is due to loss of heat from the combustion chamber. Aluminum heads transfer more heat from the combustion chamber to the cooling system then iron heads do. Any heat lost is a loss of potential power. A perfect engine would lose no heat from the combustion process. A good way to think about this is to imagine you only have so much power available. Some of that power goes to propelling the car, some goes to overcoming friction in the engine, somes goes to driving the accessories, some goes to heat loss to the cooling system, some goes to heat loss to the air, and some goes to heat loss through the exhaust system. By reducing heat loss you are putting more power to propelling the car. Essentially, you've made the engine more efficient.

The advantage of aluminum heads though is the same reason they make less power. The added heat loss makes the engine less prone to pre-ignition and allows you to raise the compression ratio on pump gas relative to iron heads. The added benefit due to increased compression ratio can be more than what you lose from heat losses through aluminum heads.... but not always!

 

By the way, I might point out that heat loss through the exhaust system is detrimental for a reason that you might not expect...

It's desirable to maintain heat in the exhaust system not because it has anything to do with the performance of the engine but because of air flow dynamics. It just so happens that when air is flowing through a pipe that it's velocity is dependent upon it's temperature. Lose heat from the air through the pipe and the air speed will reduce. Input heat and the air will speed up. That's why racers wrap exhaust systems with insulating material. It keeps the exhaust gas velocity as high as possible which allows the entire setup to make more power.

 

Now I'm beginning to understand. Thanks for clearing those questions up. What would the recommended engine gurus recommend for a nice 427 small block setup? I'll be running a dual TBI setup on top getting plenty of air and fuel and I'll probably end up having custom headers made so flow won't be a problem. I'm just trying to decide on block and heads.

 

Try this link they list the best stuff for blocks and heads

http://www.performancewholesale.com....duct_range.htm


brodix, donovan, and rodeck make the best aluminum block period dont look anywhere else.

dart makes the best cast iron block for the money about 2,000 for a fully prepped little m block my personal choice if i was going cast iron but im not al aluminum for me .

 

Hey QwkTrip,

You just saved me a bunch of writing. Thanks.

Don't forget the other reason to wrap headers. To help keep the under hood temp down so that the intake charge is cooler, and more dense.

See, if you look at all the variable heat ranges that you need in an internal combustion engine, you will start to realize just how inefficient they are.

You need the intake air cooler, so that it's more dense so more air will enter the cylinders.

But you also you need to keep the heat in the cylinders to fully burn the fuel. But at the same time, you need to keep the temp of the metal down to avoid spontaneous combustion (IE, pre-ignition). You can do that by using aluminum heads, which do not hold heat as long as iron, but in the process of loosing heat fast, they also transfer heat fast, which robs heat needed in the combustion process to burn the fuel completely.

Then you need to keep the exhaust warm so that it's less dense so that it flows faster. But you can't let the headers/exhaust manifolds get too hot or they will possibly melt. Or if they don't melt, then the gaskets will breakdown.

It's a 'cool-warm-warm' process on a very fine line. Unfortunetly, it makes elec. motors look like a better alternative. Not that I, nor any other 'Torque Hungry American' wants that to happen, but it appears to be in the stars.

Burn that petro!!!!! :rockon:

AJ