Just facts first. I think I counted 8 owners of alloy blocks on this thread who said that the reason for buying an alloy block was weight. Your BBM weighs 250 lbs and my Shelby alloy block is 125 lbs. Pond's alloy block is 135 lbs. So the weight savings is NOT EMOTIONAL to those 8 alloy block buyers. You couldn't find any "reasonable reason" for alloy, but at least 8 actual buyers on this thread found "weight savings" as reasonable. **)

Personally, I think most of us here bought a Kirkham for the liberal use of lightweight aluminum throughout the car. And some of us said that installing an iron block in a virtually all aluminum Cobra makes/made no sense.

Finally, weight savings wasn't the only reason I bought my Shelby aluminum block. The Shelby block was made in America and, at the time of purchase, was about $1,000-$1,500 more than an iron block. So, the Shelby block price wasn't a major factor for me, relative to the entire Kirkham build. Also, the Shelby block could be made into a 526 or 527 one day, if i so desired. The other blocks at the time couldn't go that big. One last reason, semi-related, is that the Shelby block was considered "beefier" and had the Shelby-specific head studs, which allowed (for lack of a better verb/term) the Shelby alloy block to withstand a higher RPM before going "kablooey."

So my alloy purchase had zero to do with emotion and had everything in the world to do with weight savings, price, beefier build, and potentially bigger cubic inches than competitors.

As for resale, 66GTK, who seems to buy and sell quite a few Cobras, mostly ERA's I'd speculate, stated that a Cobra with an alloy block is more desirable or sell for a higher price than one with an iron block. And all other things being equal when evaluating a Cobra for purchase, I'd chose the Cobra with the alloy block too.

What kind of power did the engine make. What were the specs. Did you also use BBM heads.

I didn't dyno the assembled engine. it has a 3.98 stroke (428 stroke) - i would have done a 3.78 stroke (stock 427) but there arent any reasonably priced cranks available in that stroke that I was comfortable with.

I do have the BBM heads, with a hydraulic roller cam setup. it's really nice and ridiculously overkill for the task. Blair Patrick did a great job with this for me. He is a true gentleman, and he even put up with my requests to assemble the engine myself after he did all the hard work!

I didn't mean to offend RodKnock - But IN MY OPINION, everything about these cars is emotion. The power to weight ratio is well beyond the limits of what we can fully use on the street, and beyond what the chassis can really fully handle.

If I want to go to the track, I will do better (faster and safer) in a c5 or c6 or c7 corvette. If I want to go somewhere, any other car can take me there more practically. For me, this car is purely emotion.

So, if anyone else wants an aluminum block because it is lighter, or makes their car more valuable to someone, or because they like the aluminum theme, then I 100% support them and, in fact, will openly celebrate their project. this is all about fun and camaraderie. I appreciate all of you as brothers and friends, even though I don't post here too often. (I am one of those unfortunate married individuals who has a wife that does not appreciate my hobby in any way.)

But the original question of this thread was asking our opinions about aluminum blocks. In the previous 5 engines I have built (windsor ford for mustang, cleveland for pantera, small block chevy for 57 bel air, and big block chevy for c2 corvette), i have always used iron blocks for cost and reliability.

Justin

Scoffing at extra power, or shaving weight.....i had to check if I was really on a Cobra forum. ;-)

Based upon the feedback from the hands-on technical experts in terms of reliability, quality and power output an iron block is preferred. From my personal experience FEs are temperamental enough without adding another variable to the equation.

It also depends on the type of build you’re seeking and Cobra manufacture. For some of the replicas I feel an aluminum block is probably the easiest and best path forward provided the cost is not a concern. For builds where the purpose of an old school is the intention I can see a cast iron block is preferred.

So to say an aluminum block is more desirable for resale or worth more depends on the particular car IMO. Everyone has their preference/opinion but would not make an overall claim about aluminum.

See rodneym^^^. Uh let's ask rodneym about "reliability, power output and quality". He has an all aluminum twin Paxton blown FE, IIRC. And he's driven his car 5,000-10,000 miles. I don't remember him complaining about "reliability, power output and quality." We both had our engines built by Tom Lucas here in CA. While I haven't driven as many miles, I think my engine has been quite reliable with 600+ HP, no leaks, etc.

Do cast iron blocks make more HP? Everyone seems to think so, Barry and Brent do too. But if folks believe that a 125 lbs of block weight isn't a big deal (5.5% of my Kirkham), then why does a few extra HP with a cast iron block?

Blair Patrick will also tell you that an iron block will make more horsepower without the "fickle-ness" of an aluminum block. He's not a fan either.

In my mind the horsepower difference between the cast iron block and the aluminum block would almost make up for the weight difference in a straight line, 1/4 mile type deal. A 20-hp difference is a .1 ET difference in the 1/4.

There's not that many corner-carvers on here, so I don't know how justified the loss of weight is for most Cobra owners. I think, in my opinion, that to most buyers, "all-aluminum" is a buzz-word, just like "billet" or "roller" or "forged".

I wish Richard Hudgins was still active here. I'd like to have a true chassis guy's input on how much the weight difference affects the handling of a Cobra and at what point the "average" driver would be able to tell it.

This is an interesting conversation to have at this point. Did you have this conversation with all the previous Aluminum block customers you build engines for?

A lot of guys will ask about the differences between materials and I think I try to mention it to those that don't.

However, there were engines that were built before I experienced a few quality issues and hassles. Kind of a straw that broke the camel's back type of thing. At some point, you just have to stand back and say, "I just don't feel like doing that anymore."

That's interesting. Given my time back I would have considered a iron block.
I would want to be able to get to 482 CI though.

It is a toy, not a life saving medical device.

"In my mind", if I were in the market, I'd find a competent confident engine builder who can build an all aluminum FE, because weight is important. And there are thousands of alloy blocks on the road and I haven't heard many, if any complaints. I haven't heard anyone mention alloy blocks being fickle either. And at least 8 alloy block buyers here in this thread said weight was an important factor when building their engine.

As for differences in HP between the two, post some data dump sheets of two equal engines with the only difference being the block.

Lastly, on my way to Starbucks for my morning mocha, there are two sharp turns, and I can feel the difference. :LOL:

Of course no one is going to complain. It's because all the risks are taken by the engine builders before the customer even sees it. All the customer knows is that they have an all-aluminum engine.

You haven't heard anyone mention that aluminum blocks are fickle? Did you read any of the posts by Barry or myself? You have seen a sample of one engine. I've got a sample size much larger than that....

Starbucks tastes like automatic transmission fluid. (Yes, I've tasted both.)

We know you like your engine. That's perfectly fine. I'm not building any more of them, hence the original post from 11 pages back.... :)

I agree- This thread was started to discuss casting issues with FE blocks specifically.

However- to your statement about "every other" OEM block being just fine in aluminum; well, I also agree- They are "just fine" in OEM applications... But they are not better than iron for high cylinder pressure/high torque applications.... None of them.

So, nothing I originally stated was "not true" :cool:

Example: the 2017 Corvette Z06. Comes with 650HP from an all aluminum engine, whose design has been rigorously tested to go 100k+ miles. It runs about 10.5psi of boost from the factory.

BUT- The moment you take that same Corvette to Lingenfelter Engineering, and say "I want to make 1500+HP" The first thing Lingenfelter is going to do, is try to talk you into upgrading to one of their iron truck blocks, before they even start adding boost.

I stand by what I stated: From a strength and durability standpoint, aluminum is not superior to iron for any high pressure/high performance engine block. Aluminum's only advantage is weight...


EDIT: WAIT! - I am calling BS on myself - There is indeed another advantage (besides weight) to aluminum, versus iron: Repairability- a cracked aluminum block can usually (but maybe not always) be welded, re-machined, re-sleeved, and re-used, while a cracked iron block is junk 99% of the time.

I didn't even skin a knuckle on my build.:cool: Although I do vaguely remember the builder saying something had broken off, it was a PITA to get out, and that's why it would be slightly delayed getting over to the ERA boys, but, again, no skin off my nose, knuckle, butt, toe, etc.:3DSMILE:

No, I can't remember any consumer (not engine builder) posting that their alloy block is "fickle." What does "fickle" mean? Does that mean they have to re-torque their head bolts? Don't owners of aluminum intakes (everyone) re-torque their intake bolts? According to the Shelby website, the Shelby alloy block is even stronger than the original cast iron FE block.

To a "hot rodder", weight savings is a crucial factor when purchasing parts, probably since cavemen inhabited the Earth. Cavemen and cavewomen would search far and wide for a lighter, but strong, club to hit other cavemen with. If you read the Porsche forums, those guys and gals take out their airbags to reduce weight, change wheels and seats, etc., that's how obsessed they are weight savings.

Yes, I was kidding about Starbucks coffee. Worst coffee ever. BUT! it's a helluva stock to have in your portfolio. About a 2% dividend and over the past 5 years SBUX has almost tripled in value. :D

Fickle means that they have a greater chance of developing leaks. Fickle means that there are warm-up and operating guidelines that are a little more strict because of bearing clearance.

A Shelby block is stronger than an original FE block. Not stronger than an aftermarket cast iron block. You do have reduced ring seal from the aluminum block just because things move around so much.

We're not driving Porsches. ;)

Thanks for the 11 pages of backing-and-forthing. I feel better.

Now, if you would just do exactly as I tell you, you will be healthier, wealthier and wiser than RodKnock will ever be.:cool:

Brent, I'm assuming the only reason you're seeing increased HP is due to cast iron's increased thermal retention? Once aluminum heats up and comes up to "designed clearances" ring sealing should be the same as cast iron. Blow-by and effective static or dynamic compression ratios should also be the same as iron. My training leads me to think that the horsepower differences should be minimal. Thoughts?? Just curious...

I call BS on this statement. Oh come on, you don't think we're a nation of complainers and whiners? I'd be first in line to moan about nearly everything. You name it, I'll moan about it. :LOL:

Today's "groan" here on CC? Others making global statements about the "reliability, power and quality" of an alloy block versus a cast iron block when at least 8 of 9 (jkg2101 excepted) chose alloy over cast iron for the 125 lbs weight savings.

Here's my global statement (maybe a question) for the day. Why in the world would "you" drop an engine with a cast iron block into a Kirkham or alloy CSX? Aren't all the alloy bodied Cobra owners afraid that their alloy bodies might require more maintenance, dent more easily, etc.? Aren't alloy bodies more "fickle" than fiberglass bodies? Don't lean against it? Don't drop any tools on it? And if you own a BNL (bare naked lady), HOLY COW, the extra work to keep it polished is ENORMOUSLY time consuming (it's not). Aluminum is quite "fickle."

IMO, there's a disconnect of grand proportions there.

Well, yeah, but it's more important for the Porsche guys to obsess about weight (and more importantly, about weight distribution)...

It wouldn't be such a big deal to them, if the Germans hadn't deliberately designed their cars to run around backwards... :3DSMILE::3DSMILE::3DSMILE:

just teasin'