Alloy vs. Iron blocks

[Mike]

I have searched old threads concerning alloy vs. iron blocks but cant find anything about heat buildup in the engine compartment. I am looking at ordering a motor for my SPF and was leaning towards Alloy but I have had two installers say, 1. they create a hotter engine compartment and 2. they expand and shrink causing leaks. I am looking for anyone with first hand experience, both good and bad that can shed some light on this.
Any feedback would be greatly appreciated.
Regards in advance,
Mike Murphy

 

[David]

Well I can't comment on the hotter engine compartment, although the alloy will conduct better I'm not sure that there would be a difference when 'up to temp'. It is possible that outside of the track this may result in a lower engine bay temp.

As for leaks, well almost all modern bikes and a very large number of cars manage to have alloy blocks without leaks. Yes things are different between iron and alloy blocks but a decent builder will know what to do to make a decent engine. IMO leaks are purely down to either faulty/damaged gaskets or the builder fitting incorrectly specified gaskets.

 

[Seymour Snerd]

As for leaks, well almost all modern bikes and a very large number of cars manage to have alloy blocks without leaks.

The trouble with that line of reasoning is that we are not talking about a modern engine. We are talking about block designs from the late 50's to 60's that were designed to be cast iron.

FWIW, when I was engine shopping for my SPF both Dennis Olthoff and the (at the time) Roush VP marketing (forgot name, now works for SPF) advised against aluminum for the previously-cited reasons.

 

[David]

The trouble with that line of reasoning is that we are not talking about a modern engine. We are talking about block designs from the late 50's to 60's that were designed to be cast iron.

True but you cannot take a cast iron block and 'just' make it aluminium, you have to redesign it to take into account the different properties. Or I guess if you don't it leaks...

 

[roaldin]

Mine is alloy, no leak issues and no heat issues.

Although someone once told me that they were told by someone that was an expert that the sky would fall... Sheesh this forum...

An 01e AND an alloy block... Wow I really live on the edge...
Forgive my little outburst ;p

Tim.

 

[Damian]

I my be wrong about this but I thought that the ONLY difference in NA form was weight. I know that almost all of the parts are interchangable at least when preppeing for FI. Now in a FI application and again depending on the amount of boost you would want the iron block for the strength. Again I am speaking about anything in the 1000hp and up range. Aluminum can live well at the 650hp range NA. What it all comes down to is cooling so your engine builders are incorrect. one something is cooled at a certain degree it doesn't matter what the material is as temp' are temps regardless of what metal used.
Now older BLOCKS DID HAVE DIFFERENT COOLING PATHS. Think LT1 to LS1. So in short if you are not going with an FI application get yourself an nice aluminum block and just make sure to cool it properly. Now all of this has been simplified for quick reading. You should look at some LS forums and see what aluminum blocks are doing these days!!!!! Heck some billet blocks are just insane!!!!

 

[Rich A]

1. they create a hotter engine compartment and 2. they expand and shrink causing leaks.

Mike,
First hand first hand experience here.

1) The engine compartment still gets hot, hotter is not possible.
No matter what engine (same CID and compression) Alloy or Iron the engine temperature will be the same,
provided then have the same cooling systems. Just one of them will dissipate heat faster (aluminum).

2) Expanding and shrinking has been factored/designed into the engine by manufacture, so that usually is not a problem.
The problem causing leaks are poor casting, damage to the sealing surfaces, and non frequent coolant changes.
Out of the 5 years/thousands of aluminum engines I worked with only one had a casting issue.
Damaged sealing surfaces and non frequent coolant changes are the most common cause for leaks.
Again that might be different depending on the manufacture who cast the heads and blocks.

Just my 2 cents

 

[Ian K]

Warping of aluminium engine parts has been an issue since they started using it. The old Z cars were notorious for cylinder head warpage.

However, the problem is when the aluminium overheats and cools too quickly, or when it just cools too quickly. Which indicates there is a problem with your cooling system, or someone pulled the parts while they were still hot. Under normal working conditions, aluminium blocks are fine barring manufacturing issues.

Ian

 

[Larry L.]

FWIW, when I was engine shopping for my SPF both Dennis Olthoff and the (at the time) Roush VP marketing (forgot name, now works for SPF) advised against aluminum for the previously-cited reasons.

Mark Yagelo @ Roush was very emphatic when he advised me to go the iron block route (we were discussing their 427IR). He said their (Roush's) experience over the years was that there often were "heat issues" when using alum blocks.

I didn't think to ask at the time if he was specifically referring to just the WINDSOR design alum blocks or not. 'Wish I had.

 

[Randy V]

I worked on a Late Model stock car team 10 years ago - so maybe things have changed since then. Using DART SBC blocks that were wet sleeved cylinders, all of them leaked coolant into the oil and we had to use Moroso Ceramic Block Sealer on them while on the dyno in order to get them to seal up.

The weight savings was not as great as what you would think. It takes a lot more aluminum to come up to the same level of strength as iron. Therefore a mold for an Iron block would most likely yield an aluminum casting that was not as strong as the iron version from the same mold.

 

[Rod]

Shelby redesigned the FE block in aluminum and I have owned one for 5 years with no leaks.

As for what anyone says at Roush.....

Roush has had a documented history of leaking and other issues. I personally wouldn't rely on what anyone had to say from that company. Every time someone brings up the Roush "issue" over on ClubCobra, an argument ensues. In fact, in a recent thread, a Backdraft dealer has said that its become difficult to get Roush engines nowadays. Folks like me are left to guess why.

 

[Terry Oxandale]

Aren't part of the problems related to the expansion coefficient difference between iron and aluminum parts?

 

[Rod]

The weight savings was not as great as what you would think.

I don't have the Windsor block weights off the top of my head, but I do have the various FE block weights rolling around my thick skull.

Factory Iron 427 FE 195 lbs
Pond Aluminum 120 lbs
Shelby Aluminum 125 lbs
Genesis FE Iron 235 lbs

 

[Mike]

Thanks for all the replies. Please keep them coming. I specifically was vague in order to keep it as close to topic as possible without getting into motor size, and even worse, who would supply the motor.

I have a SPF Mk111 already with a 514 Keith Craft motor and have had no issues. I recently ordered a SPF Mk1 and thus all the questions now. I plan on doing this once and obviously everyone has their own idea of their perfect GT40.

I again find myself leaning towards a KC 427 small block (351 Windsor block) for a couple reasons. I like the motor I have from KC. They will make suggestions and also change some items if requested. Alloy is an option with KC and according to the Dart spec sheet, the Iron block is 195 pounds while the Alloy block is 93 pounds. That is a significant difference. I also plan on using the car at the track occasionally and have decided on a Dry Sump setup if that makes any difference in regards to the Alloy vs. Iron block.

Now with all that being said, the reason I first posted the question is that SPF is very loyal to Roush and strongly recommends their engines. I have no doubt they make a great engine, but as I stated above, I really want to do this once and if Alloy is a good reliable option, I want to hear from the ones with first hand experience.

Thanks,
Mike Murphy

 

[Kelly]

Aren't part of the problems related to the expansion coefficient difference between iron and aluminum parts?

Yes. Funny how people don’t seem to be bothered by bolting aluminum heads to an iron block yet the head will grow more in length than the block and must move on the head gasket through thermal cycles. On an alloy head and block you don’t have the contribution of dissimilar coefficient of linear thermal expansion of the two different metals but heads and blocks operate at different temperatures anyway so you will always have some temperature induced differences in growth between parts.

It’s true that alloy can be more susceptible to porosity than iron but it’s more of a quality control issue. It’s also true that without proper cooling, particularly in the area of exhaust ports and combustion chambers material properties can be altered in the age hardenable aluminum alloys but again, I don’t see it as an inherent or avoidable issue. I also wouldn’t worry too much about differences in engine bay on alloy versus iron when you have all the exhaust surface area of the 180s driving that train.

I think the biggest issue in use of alloy blocks in pushrod engines is the control of valve lash. When all the static structural engine parts are aluminum and all the moving parts are steel, there can be some significant differences between hot and cold lash settings and they get much tighter cold. More susceptibility to bent push rods from romping them before they come to temp and loosed up. Same is true in an aluminum headed iron block engine, or all iron engine, it’s just accentuated with the addition of the alloy block and matter of degree.

-My 2 Cents.

Best,
K

 

[Steve C]

P2125 has Keith Craft built Shelby Al block with E'brock Al heads and Al intake.

No leaks anywhere after 3 yrs and 6,000 miles (not even a drip from the rear main).

I'm happy I went Al and very happy with the Shelby block and KC build

Steve P2125

PS: Think the secret is to go all Al and with a good builder.

 

[Cliff Beer]

An alloy block of similar rigidity as an iron will seal just as well, and perhaps better, with alloy heads. The head gasket will see less movement when both block and head are alloy - that's a good thing.

The reason a lot of all alloy engines leak (think ferrari.....) is because a) the alloy block is rarely as rigid/stiff as would be an iron block, and b) alloys can take a non-flat set much more easily if they're run at high temps, both block and head.

So, net, if the alloy block has the add'l webbing and wall thickness to be as stiff as the iron block (and everything else being equal) then it should seal just as well as an iron block with alloy heads. This means that you need to take a hard look at that alloy block and see if it has the necessary girth and structure to be equivalently stiff as the iron block. And, of course, adding wall thickness and webbing adds weight, lessening the weight advantage of alloy v. iron.....

 

[David]

I don't have the Windsor block weights off the top of my head, but I do have the various FE block weights rolling around my thick skull.

Factory Iron 427 FE 195 lbs
Pond Aluminum 120 lbs
Shelby Aluminum 125 lbs
Genesis FE Iron 235 lbs

Are those bare block weights or short block weights?

 

[Rod]

Are those bare block weights or short block weights?

Bare. Info per their websites.

 

[Steve Wood (PANAVIA)]

Rod, - keep in mind that the Shelby FE block is getting updated, so it may end up being heavier -