BBM vs Pond Aluminum block for new SOHC build

[338Raptor]

I’m within about 6 months from starting an Aluminum SOHC engine build for my 67 fastback. I have been researching the specs of each component I will need. My goal is 800hp and high 600’s torque (700tq would be ideal). I’m confident with all the parts and pieces I have selected my goal is achieveable. My concern is with the Aluminum FE blocks.  I’ve read several threads about HP loss in aluminum blocks when compared to Iron blocks.  I understand I will likely give up 30+ horsepower with an aluminum block vs an Iron block. I’m OK with that since the weight advantage of aluminum will reduce my cars front end weight by 100 lbs. My concern with the aluminum blocks is cylinder distortion and ring seal. I plan to use a Napier lower compression ring and Total Seal gapless upper ring.  This may help but not solve the real issue.

My question for this group is:
1. Will the BBM or Pond aluminum blocks handle my build?
2. Or should I pony up the extra money for a Shelby aluminum block?
3. Or should I forget about aluminum and buy an Iron block?

More details on my build:
93 octane
Hilborn EFI
510 cid
4.375” 4340 crankshaft (probably custom Scat)
4.310” pistons (if the liners/block can handle this large bore)
11:1 compression
Pond SOHC heads
T&D steel rockers
Holly HP EFI
Cam specs are still undecided but they will need to be big
90% street, 10% drag use. And maybe even a little autocross.

[blykins]

1.  Yes.
2.  I don't see the need.  The aluminum blocks are pricy enough.
3.  Yes.

Everyone knows I stay clear of aluminum blocks when I can, so call me biased.  But I'm just not a fan.  They have their place, but IMO that's a very small niche.  Paying an extra $2200-3700 for a block that will noticeably be down in horsepower in comparison to a cast iron piece, in a 90% street car just doesn't seem prudent to me.   There's also extra block prep and machine work involved which adds to the cost.

Most of us that have built a few of each notice anywhere from 30-40 hp difference on similar builds.  The general "rule of thumb" is that 20-25 hp will change your ET by .1 second.  There's also a general "rule of thumb" that dropping 100 lbs will decrease your ET by .1 second.  In a street/straight-line situation, the savings of weight of the aluminum block won't really give you any performance advantage.  If this were a roundy-round application, or another race class that focuses on weight reduction, then there would be a benefit.   

Your ring seal loss comment is the key here.  On an all-aluminum engine build, valve lash/preload changes by about .014".  Compare that to an iron block/aluminum head combo, which changes about .006".  Unfortunately, aluminum has a much higher heat expansion coefficient and the blocks move in every direction. 

The pros of an aluminum block is that you can change sleeves if the cylinders are worn.  They are also easier to repair if you decide to window one.

Whatever you do, make sure and have it pressure tested and/or sealed internally.  Casting aluminum is hit or miss and I've had to reject multiple aluminum FE blocks because of porous areas behind the lifter bores that leak air on a pressure test.

BTW, with reference to your camshaft note, you'd be surprised at how low duration/lift you need with well-flowing heads, even on a 500+ inch engine. 

[GerryP]

If you want an aluminum cammer, then get an aluminum cammer.  Screw the data.  If all we do is crunch numbers when making decisions, then there's no passion in living.  How many opportunities are you going to get for a '67 Mustang with an aluminum cammer?  Go for the gusto, my friend and screw the data.

[blykins]

I think "all-aluminum" has become one of those hot-rod buzz words.....something that people crave to own but they don't really understand why.  Same deal with 6-speed transmissions.  Maybe because of the rarity?  Price? 

I've got a good buddy who's a "car guy" but just doesn't understand a lot about them if that makes any sense.  He was in my shop the other day while I was assembling a 347.  "What's that?"  "A 347."  "Ooohhh, I'd love to own one of those."  I feel like he'd pass up a 351, 393, 408, etc., just because the 347 is more of a buzz word.   He's also a Chevy guy and wondered why I suggested for him to build a 400 instead of a "383". 

[turbohunter]

I’m still horny for an aluminum block to knock a couple hundred pounds off the nose of my mustang.
Totally get the straight line argument but how sweet to have an all aluminum big block ‘stang.
Of coarse as long as it’s taking me to get an iron block in it I might be doing aluminum from my grave.

[gt350hr]

   Pond block for aluminum.  BBM is OK for iron but so is the Pond iron block.
  Brent's points about the iron block being more powerful are all valid . The only advantage ( besides the wow factor) to the aluminum block is that "nose weight" which is oh so critical when cornering is a must. Your Horsepower goal can be reached with either block material.
  Randy

[blykins]

   Pond block for aluminum.  BBM is OK for iron but so is the Pond iron block.
  Brent's points about the iron block being more powerful are all valid . The only advantage ( besides the wow factor) to the aluminum block is that "nose weight" which is oh so critical when cornering is a must. Your Horsepower goal can be reached with either block material.
  Randy

I think for $2500, I could find other places to save/relocate weight.....LOL

[338Raptor]

 
I have a couple questions from blykins post.
Is the valve lash differences between aluminum vs Iron blocks really an issue on a cammer?  I can see that being an issue on a push rod engine but the cams/rockers are all in the head of the cammer.
Also, I didn’t mention this earlier. My fastback is setup with road race suspension so I would like to optimize my cars handling with light weight parts. That’s my primary reason for looking at Aluminum.
I hope you don’t take my questioning your comments the wrong way. I did ask your opinion and I do appreciate the points you bring up. It’s all going to help me make the right choices for my build.

I should mention. As for the additional cost of an aluminum block for a cammer.  I think common sense $/horsepower reasoning is probably out the window on any cammer build. But like many I want the car/engine combo to be kinda period correct even if a Mustang never had a cammer factory installed. I still want to save money wherever is possible (ie. Shelby block) but truth be told we all know I could build a stroker 460/557 at 1000 horsepower for half the cost. In fact I have one in my mud truck.

[fekbmax]

If you do go aluminium,  I'd go with the pond block as well. The BBM piece looks awesome in pictures but how many of them really exists and out of those how many really get used beyond a show car cobra or something that gets driven back and forth from the trailer to the spot at the car show. Pond has been doing aluminum blocks for quite a while and there are many that really get used and regularly beat on at the strip. Pond is also great to work and deal with and freely will give you honest and any information you may want or need. I to have always wanted a Shelby block but unless I'm turbo'ing or pro charging I cant see spending the extra $2500.oo for a Shelby over a pond. I also think pond is your best bet at actually getting one unless things have finally changed for the better. Also, nothing against BBM, I'd surely use one if that's what I had or all I could get. They look like nice pieces, I'm assuming BBM finally has them available? I along with the chatter of a few other builders talked myself out of another aluminum block (for now)  because of all the points Brent mentioned and also because my machine shop friend passed and I wouldn't trust any of these shops around here to handle an aluminum block correctly. 
Good luck to you and keep us posted. 

[fryedaddy]

   Pond block for aluminum.  BBM is OK for iron but so is the Pond iron block.
  Brent's points about the iron block being more powerful are all valid . The only advantage ( besides the wow factor) to the aluminum block is that "nose weight" which is oh so critical when cornering is a must. Your Horsepower goal can be reached with either block material.
  Randy

I think for $2500, I could find other places to save/relocate weight.....LOL

i put my battery in the trunk,put on alu heads,intake,radiator,and water pump and it took 150+ pounds of the front of my car.it even brought my headers another inch off the ground.really noticeable diff in the cornering too.i wouldnt want to give up 30 hp for alu block,my goal is to squeeze every hp out of what i have.i actually ordered a alu block,they werent in stock at the time.when i read about the hp loss i canceled my order.jmo

[e philpott]

What is the actual weight difference between a all aluminum complete cammer (ready to install) verses  a cammer with aluminum heads and iron block ready to install ? I'm afraid to ask what a all iron cammer weighs , lol

[fryedaddy]

seems the only main weight diff would be the top end

[blykins]

 
I have a couple questions from blykins post.
Is the valve lash differences between aluminum vs Iron blocks really an issue on a cammer?  I can see that being an issue on a push rod engine but the cams/rockers are all in the head of the cammer.
Also, I didn’t mention this earlier. My fastback is setup with road race suspension so I would like to optimize my cars handling with light weight parts. That’s my primary reason for looking at Aluminum.
I hope you don’t take my questioning your comments the wrong way. I did ask your opinion and I do appreciate the points you bring up. It’s all going to help me make the right choices for my build.

I should mention. As for the additional cost of an aluminum block for a cammer.  I think common sense $/horsepower reasoning is probably out the window on any cammer build. But like many I want the car/engine combo to be kinda period correct even if a Mustang never had a cammer factory installed. I still want to save money wherever is possible (ie. Shelby block) but truth be told we all know I could build a stroker 460/557 at 1000 horsepower for half the cost. In fact I have one in my mud truck.

The issue with lash is because of the aluminum parts growing faster than the steel parts (pushrods, etc.) on a wedge engine.  I've never built an all-aluminum SOHC engine, so I'd have to defer that question to Jay or Barry. 

Two things that would remain consistent between a SOHC and a wedge all-aluminum FE are the compression ratio changes and main bearing clearance changes when hot.  All of this has to be allowed for in the design and setup stages of the engine.  The blocks expand with heat, so the block actually expands up past the piston (so when hot the piston would be further down in the hole at TDC) and the main bearing bores grow.   On all-aluminum FE's, I would set the main bearing clearances up at .0018-.002" cold, as opposed to .0028-.003" with an iron block.   All of that growing and contracting can be a little harder on the gaskets.....especially the oil pan gasket. 

Everyone wants what they wants, but I always like for guys to have all the facts in front of them before making a decision. 

[Chrisss31]

I'm surprised that no one has come up with a CNC program to lighten up a BBM or Pond cast iron block.  There has to be some potential to shave weight off of one of those blocks without taking too much away from the integrity.

I was hot for an aluminum block when I started my Mustang project a few years ago.  I talked to an engine guy and he advised me that unless the weight was critical the power gain more than offsets the weight savings.  He also advised that a Ford block would be just about as light an a modern aluminum block.  He also added that Shelby blocks are the heaviest of the aluminum blocks.  I believe this all to be true.

[338Raptor]

Does anyone have first hand knowledge or experience with the BBM aluminum block?  Can anyone say with confidence it is as strong as the Pond block?