I have five aluminum FE blocks, four Shelby and one Pond. The Shelby blocks are far superior in my opinion. I would not trust a Pond aluminum block past about 700 HP. I had an 840 HP SOHC with my Pond aluminum block and the block couldn't take the power/RPM; main bearing bores distorted, spun the #2 main, lost oil to two rods and blew the motor going down the track. My Shelby blocks on the other hand have been trouble free, and are much, much beefier around the main web than the Pond block. My naturally aspirated Shelby block SOHC makes just over 1000 HP, and I've made just over 1200 HP with supercharged FE on another Shelby block. No concerns with that one.
The problem with the Pond block is that it uses the same casting patterns as the cast iron block. The area around the main bearing bores is strong enough in iron, but not in aluminum. The Pond aluminum block is fine up to 700 HP, and I've used mine there with no issues, but one thing that I did notice is that even at those power levels, every time the block was torn down to be freshened there was evidence of cap walk. And its not that cap, because the Pond caps are very beefy. Its the block itself.
Here are a couple pictures illustrating this issue, Pond block first. By the way, this block is now junk after tossing two rods after the main spun, so it was sitting outside for a while, hence the rust:
Any doubt as to which is stronger?
Also, I strongly disagree with the other comments in this thread regarding aluminum blocks. In my opinion, aluminum blocks are far superior to iron blocks for several reasons. From a weight perspective, a bare Shelby block weighs about 130 pounds, whereas a BBM cast iron block weighs about 270 pounds. That is a big difference that will affect acceleration, braking, traction, and cornering. Further, I have never seen definite proof that a cast iron block makes more power than an aluminum block. Everybody says this, and maybe it's true, but I have never seen a definitive back to back test. Someday I'm going to do one myself. Being able to replace a sleeve in an aluminum block, in case of damage, is a big advantage, and aluminum blocks are much easier to repair than a cast iron block. I had the pin end of a rod give up on my big SOHC with the Shelby block back in 2013, and the rod came through the block, but despite extensive damage the block was able to be repaired and went back to making 1000+ HP the next year. But the big advantage is weight savings.
Also, any comments regarding checking an aluminum block when you get it also applies to any aftermarket cast iron blocks. BBM cast iron blocks have had porosity and leak issues, so have Sideoiler garage blocks from what I've been told. Any aftermarket block needs to be checked, and all should be subject to the same basic machining operations. My Shelby blocks did not require any more machining than an aftermarket iron block; just a power hone to fit the pistons and an align hone of the mains.
If you have a horsepower target, you can reach it with either a cast iron block or an aluminum block. Why not take advantage of the aluminum block's light weight? Seems like a no brainer to me, except for the cost factor, and as mentioned if you are going to build an SOHC, what's the difference? Its going to cost a lot no matter what.
I don't know anything about the BBM aluminum block, but I would wonder if it is a dedicated aluminum design (like the Shelby block), or an aluminum block that is cast with the cast iron patterns (like the Pond block). If it is not a dedicated aluminum design, I would steer clear of it.
One other thing about Shelby blocks, is that I have heard for a while they went to an aluminum main cap, rather than steel. That was a bad idea, and would make me steer clear of them also. Now they are supposed to be back to the steel caps, but if you call Shelby for a block make sure to ask about that.
My advice - get a Shelby block.
