Cast iron block vs. Aluminum block

[yeasure]

Sorry to break the topic but Slick i see you're in Asheboro, so am I(kinda) send me a pm if you get a chance.....thanks

 

[Detroit_Doc]

Anyone that thinks a well engineer aluminum block can't withstand massive amounts of HP needs only to look at formula 1. I only bring this up because someone mentioned NASCAR. And well, if you compare NASCAR iron blocks to Formula 1 aluminum blocks, that would be like comparing cavemen to spacemen.

I used to race a formula car (albiet a poor mans formula car) in the SCCA. I looked at lot of research into chassis building. The most intriguing thing I found was that a 2" .003 DOM tube is stronger than a 1" .006 DOM tube. I don't pretend to understand the physics, but the jist is that the .003" tubes weight less than the .006" tubes. Because the lighter tube can have a wider diameter, that makes them stronger in tension and compression. So as long as the engineer ensure the tube will only be put in tension and compression, they can use the lighter tubing and enjoy both a weight savings and strenght increase. If the tube is put into other stresses such as sheer, then all bets are off.

So a lighter aluminum block may resist stess better due to wider walls under the same principle.

 

[PowerWheels]

What does a Top Fuel NHRA 8000hp engine use?, I think that is your answer! You guys crack me up, most of you won't approch the limit of the block, but you will argue all day long about it. If ford wasn't sure of the design of the aluminum block, then I am glad they put the iron one in.

Why don't they make a forged block? That would end the discussion.

 

[Jpjr]

Anyone that thinks a well engineer aluminum block can't withstand massive amounts of HP needs only to look at formula 1. I only bring this up because someone mentioned NASCAR. And well, if you compare NASCAR iron blocks to Formula 1 aluminum blocks, that would be like comparing cavemen to spacemen.

I mentioned NASCAR. And I also mentioned that aluminum blocks are literally banned at all kinds of race tracks across the country.

The reason is MONEY. Compare the cost of a NASCAR iron block, which you could build out of a Summit catalog, and a F1 aluminum block, which probably get built by NASA . That is the point. High-performance aluminum blocks show up in Ferraris and F1 cars because they are simply a lot of $$$. People racing thier beat up monte-carlos at the track on weekends are not going to have Teksid blocks under the hood. And if they were racing cheap alumminum motors, one could make the argument that they are more prone to failure under high hp applications which could lead to more accidents.

This is the whole point of my original post. The iron blocks in our cars are 'caveman', like NASCAR, but extremely reliable and cheaper. For those of us that don't know enough about well tooled aluminium, it seems like the less risky application. That said, I've at least 5 times within this thread acknowledged to Hissman that a well tooled aluminum block, like a Teksid, can outperform many iron blocks. That's something to be said as I had no idea aluminum was being used for such extreme applications.

 

[yeasure]

Please correct me on this anyone, but hasn't Johns car been running the same block for over 4+ years(in that area)?
Btw if this is correct thats the fastest mod motor we have and that would be an aluminum 4.6 block.
John has ran that car a lot honestly so i think it's proof enough for me they can hold up nice :thumbsup:

 

[orange2004cobra]

Aaron Archers car runs 8.46 all day long, and has an aluminim {stock 4.6} block in it..
And that engine has been ran in 2 race cars, through 4 seasons, on the same stock aluminum block..
L.

 

[mike69440]

Question on the 5.0L 4V crate motor

Question on the 5.0L 4V crate motor?

What does it have for Rods, Pistons and pins?

Who makes the Block?

Anything Special about the block?

Can block be purchased as a seperate item?

Anyone?

Thanks!

 

[Bob Cosby]

GT blocks and blowing them up was mentioned above. As an FYI, all Mustang GT blocks prior to 05 were iron - not aluminum. Also, as was correctly stated, the block had nothing to do with failures related to supercharging.

 

[Machinator]

Would i like for my car to be 200lbs lighter? Sure. Could an aluminum block handle the stock power our engines put out? Maybe...probably not for long.
But it deffinenly would'nt handle the power for what i have in mind for it.
Jay.

The 96-98 blocks are to this day the strongest 4.6 block made ,aluminum or iron.

 

[SlowSVT]

Aaron Archers car runs 8.46 all day long, and has an aluminim {stock 4.6} block in it..
And that engine has been ran in 2 race cars, through 4 seasons, on the same stock aluminum block..
L.

8.46 seconds is not "all day long". Try more like 8.46 second. Would you put that aluminum block in an off-shore racing boat? They all run cast iron blocks in racing boats due to the extra durability they provide for continuous high loads they must endure.

Anyone who suggest that aluminum is stronger then cast iron should have their head examined. Why do you think Ford decided to use cast iron in the Cobra motor while they used aluminum in the Mach 1. Aluminum is nowhere as stiff as cast iron and has almost 3 three times the thermal expansion rate of cast iron. Aluminum soaks up heat like a sponge while cast iron rejects heat. Actually a cast iron motor will make a little more power then an aluminum one for this reason.

The only advantage aluminum has over cast iron is it's lighter and can be repaired. Break a cast iron block and it's a throw away. A bare Cobra block weighs 153 lbs. vs. 85 for the aluminum block.

Cast iron offers an added degree of insurance for a high horsepower street car that you want to get 100,000 miles on.

 

[HISSMAN]

8.46 seconds is not "all day long". Try more like 8.46 second. Would you put that aluminum block in an off-shore racing boat? They all run cast iron blocks in racing boats due to the extra durability they provide for continuous high loads they must endure.

Anyone who suggest that aluminum is stronger then cast iron should have their head examined. Why do you think Ford decided to use cast iron in the Cobra motor while they used aluminum in the Mach 1. Aluminum is nowhere as stiff as cast iron and has almost 3 three times the thermal expansion rate of cast iron. Aluminum soaks up heat like a sponge while cast iron rejects heat. Actually a cast iron motor will make a little more power then an aluminum one for this reason.

The only advantage aluminum has over cast iron is it's lighter and can be repaired. Break a cast iron block and it's a throw away. A bare Cobra block weighs 153 lbs. vs. 85 for the aluminum block.

Cast iron offers an added degree of insurance for a high horsepower street car that you want to get 100,000 miles on.

Man you really need to research what we are talking about. We are comparing cobra blocks, not cigarette boats here. The Teksid Aluminum Block is stronger than any other Block ford has in production. Period. Not due to material, but design.

 

[SlowSVT]

Man you really need to research what we are talking about. We are comparing cobra blocks, not cigarette boats here. The Teksid Aluminum Block is stronger than any other Block ford has in production. Period. Not due to material, but design.

Hissman, why don't you present some actual technical information rather then making generalized statements. It's funny how you just dismiss the merits of cast iron. My referring to the exclusive use of cast iron in offshore racing boats was to prove a point. Under those conditions of continuous high load/RPM in that application would turn your Teksid block into a pile broken peices of expensive
metal. Is there any truth to what I posted?

Your an Engineer, you should be able to present a better argument then this.

 

[HISSMAN]

Have you read this whole thread yet?? The arguments are there. It is the design of the block. If they made an iron block with the same engineering specs then yes, it would be stronger than the aluminum block, but they don't. I am not wanting to argue. We are talking about the Ford/Teksid blocks only. Read the whole thread, including any links to other sites that are posted in it. I have an Iron Cobra block, and as soon as I can afford it I am going to find and buy a 98 or 99 Teksid Cobra block and swap. I wouldn't do that if I did not believe 100% that the aluminum block could not take everything I am going to throw at it.

 

[orange2004cobra]

Yeah, your right, ferarri and lamborghini have no clue what theyare doing....
Aluminum.. Cheap brittle stuff...
L.

 

[SlowSVT]

Yeah, your right, ferarri and lamborghini have no clus what theyare doing....
Aluminum.. Cheap brittle stuff...
L.

No, only you have no clus (what ever that means) what you are doing. Besides, no one on this thread ever suggested aluminum is a bad engine material.

Can you imagine a cast iron V12 Ferrari engine (or one with 100K miles on the clock for that matter). The thing would be sitting on it's suspension stops.

 

[Screamn03]

Question on the 5.0L 4V crate motor?

What does it have for Rods, Pistons and pins?

Who makes the Block?

Anything Special about the block?

Can block be purchased as a seperate item?

Anyone?

Thanks!

You can purchase the block seperate for a sug retail price of 3100 :uh oh: .

 

[Screamn03]

So if I was to build a motor for my car and used the Teksid block what would be a safe power level to run it at on the street. Is there any block prep that can be done to increase its strength? As far as the ribs in the valley, can those be added to the newer blocks to strengthn them up->more like a brace setup that could be welded in? Almost a hundred pounds off the front end is very attractive and I've always thought about this issue in case I have to put together a motor for the car.

 

[tjvineyard]

Cast iron is much stiffer and stronger then aluminum and will provide much better durability in the long run.

In most situations, you can design any part of aluminum (including a block) and make it as strong or stronger than an iron piece. Generally, you have to use more material (hence a larger aluminum connecting rod as compared to its steel counterpart) to get the same performance, but the final product is generally still lighter despite the larger size.

It is also imporant to note that "stiffer" and "stronger" do not always go together. Going back to the connecting rod example, aluminum rods are preferred in many engines because they actually "give" a little bit. The designed stretch and compression of rod actually absorbs stress.

It is thermally more stable then aluminum and has 1/3 the coefficient rate of expansion which means it will maintain dimensional stability better.

I have never heard of a "coefficient rate" so I am not sure exactly what you are referring to. However, because engines operate in a fairly limited temperature range (compared to the range you are likely referring to for metallurgic properties), thermal expansion can be compensated for fairly readily. Sure, forged pistons make some noise warming up, but once in range they function effectively. The same holds true for a block.

Now, I also assume, that in this theoretical engine that we are each choosing, that you are going to put iron heads on your iron block. If you are concerned about thermal expansion rates, this is where it would be most obvious. You do not want your heads and block expanding at different rates, do you? Or is the expansion negligible and controlled enough that you can compensate for it?

Cast iron is a poor conductor of heat (higher heat rejection) and will provide a more uniform thermal expansion rate over the entire structure where as aluminum will exhibit more local heating and cooling over the same area which can result in thermal induced stresses due to the heat disparity throughout the casting.

This is the one that forced me to respond.

How would it have superior heat rejection if it is a poor conductor? Heat is rejected from the surface based on the temperature differential from the interior (chamber) to the exterior (engine compartment). The differential is substantial. A better conductor would move heat away faster (higher heat rejection) and a poor conductor would move it away slower (lower heat rejection).

Further, you want to KEEP heat in the chamber on the block side. This is the beauty of a "reverse" cooling system. Ask Smokey Yunick - cold heads and warm block make power. You WANT relatively low heat rejection in the block. You actually had an argument for your iron block there and undermined it.

Finally, you seemed to be back on the right track when you said that aluminum would have more localized heating and cooling (I think you were now associating higher heat rejection with an aluminum block) and indicated that this would be uneven. Since the aluminum block is a better conductor, the law of thermodynamics indicated that it is LESS likely to have regional temperature differentials. Heat stabilizes itself and does so more quickly and efficiently in better conductors.

TJ

 

[SlowSVT]

In most situations, you can design any part of aluminum (including a block) and make it as strong or stronger than an iron piece. Generally, you have to use more material (hence a larger aluminum connecting rod as compared to its steel counterpart) to get the same performance, but the final product is generally still lighter despite the larger size.

You seem to be under the impression that I think aluminum engines are “bad”. Not at all. The topic of this post was comparing the durability of an engine made with either cast iron or aluminum Yes you can beef up an aluminum block but the same can be said for cast iron one as well. Cast iron engine components will always be stronger and more durable then aluminum given the same dimensional restrictions like crank saddles or cylinder wall thicknesses. Do you agree?

It is also imporant to note that "stiffer" and "stronger" do not always go together. Going back to the connecting rod example, aluminum rods are preferred in many engines because they actually "give" a little bit. The designed stretch and compression of rod actually absorbs stress.

The only place I am aware of the use of aluminum rods are in Top Fuel dragsters which are used to cushion the crank from the shock of the combustion process. They are quickly discarded due to their lack of fatigue resistance. You would not put aluminum rods in your daily driver and expect it to last very long. Cast iron rods are quite common in passenger car engines and will last for thousands of hours if not indefinitely.


I have never heard of a "coefficient rate" so I am not sure exactly what you are referring to. However, because engines operate in a fairly limited temperature range (compared to the range you are likely referring to for metallurgic properties), thermal expansion can be compensated for fairly readily. Sure, forged pistons make some noise warming up, but once in range they function effectively. The same holds true for a block.

What was meant by that was since cast iron is such a poor conductor of heat it tends to distribute it more evenly so local expansion rates are not as much of a concern. Aluminum is such a good heat conductor that you need to pay closer attention to the distribution of cooling flow. Disparities in expansion rates will lead to thermal induced stress which can cause distortion and fracturing

Now, I also assume, that in this theoretical engine that we are each choosing, that you are going to put iron heads on your iron block. If you are concerned about thermal expansion rates, this is where it would be most obvious. You do not want your heads and block expanding at different rates, do you? Or is the expansion negligible and controlled enough that you can compensate for it?

Aluminum heads on a cast iron block use to be a big problem (remember the Vega). It appears Detroit has been doing a better job at distributing the cooling rates between the block and heads

This is the one that forced me to respond.

How would it have superior heat rejection if it is a poor conductor? Heat is rejected from the surface based on the temperature differential from the interior (chamber) to the exterior (engine compartment). The differential is substantial. A better conductor would move heat away faster (higher heat rejection) and a poor conductor would move it away slower (lower heat rejection).

I used this term “heat rejection” incorrectly; I should have worded it as “poor thermal conductor”.

Further, you want to KEEP heat in the chamber on the block side. This is the beauty of a "reverse" cooling system. Ask Smokey Yunick - cold heads and warm block make power. You WANT relatively low heat rejection in the block. You actually had an argument for your iron block there and undermined it.

Don’t you have this backwards. The greater the heat differential, the higher the heat transfer rate. You don’t want the engine to absorb the heat. 75% of the energy stored in the gasoline will be generated as heat rather then mechanical output. A perfectly efficient engine would not need a cooling system at all. An aluminum engine will make less horsepower on a dyno then an equivalent cast iron one for this reason.

Finally, you seemed to be back on the right track when you said that aluminum would have more localized heating and cooling (I think you were now associating higher heat rejection with an aluminum block) and indicated that this would be uneven. Since the aluminum block is a better conductor, the law of thermodynamics indicated that it is LESS likely to have regional temperature differentials. Heat stabilizes itself and does so more quickly and efficiently in better conductors.


This is true, but remember. We have a cooling system involved. Aluminum will give up heat just as readily as it absorbs it and will transfer it rapidly to any conductor that will accept it. Cast iron is such a bad heat conductor it’s not very good at getting rid of it and will retain heat much longer then aluminum will.. All the heat comes from the top of the engine and works it way south.

To me comparing cast iron and aluminum with regard to heat is like comparing Speedy Gonzalas and 2 ton elephant. Cast iron is a much denser material then aluminum on a molecular scale (now I’m starting to exceed my level of expertise) hence it higher atomic weigh. Aluminum also looses it’s strength and melts at a much lower temperature then cast iron (aluminum melts at about 1320◦ vs. 2200˚ for cast iron).

Keep in mind the topic of this post was to compare the difference between an aluminum block to a cast iron one. As I stated, In my opinion the only advantage to an aluminum block over a iron block is the weigh savings and reparability. Yes you can beef up an aluminum block and they are strong, but you can do the same thing to an iron block and it will be stronger. Iron is more tolerant of heat and is dimensionally more stable. We are getting 600-700 hp on our 4.6 Cobra engines on pump gas very easily which was unheard of 20-30 years ago which I find amazing. 98% of the guys here drive their cars on the street and reliability is a big deal to them. As you know running a car on the street is not the same as a race motor. Those engines get torn down every other week and twice on Sunday’s. Some people will have no problems running aluminum block at high horsepower levels but for me I want the added security that an iron block will afford (I guess the Ford engineers felt the same way I do). Once I screw my 600 hp Kenne Bell Cobra engine together I don’t wanna take it apart for a long time…..hopefully.

JT, I actually enjoyed your post. You presented information that I have overlooked and was bit more informative then some of the responses I have read. And it was kinda refreshing that you didn’t even mention the Teksid block not once.

Sorry for the long post.

Be well



TJ

SlowSVT

 

[orange2004cobra]

SlowSVT, I will tell you what, there are more aluminum block cobras on the road than there are Iron ones..
As far as me "not having a clue", I have built, taken apart, modified, seen modified Cobra engines more times than you have looked at your mamas face.
This thread wasnt a pissing contest, it, I thought was a quest for opinions, wich of course, are like assholes, and you my friend have 2..
L.
BTW, the last Cobra engine we built had 168,000 miles on the odo before we went inside it, .20 over bore, and good to go... Now has another 10k on it with no pros.
I believe aluminum is just fine....