BBC Block, aluminium or iron?
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Aluminum wins do to repairability. My Motown iron 427 small block bare casting was $2300. The aluminum block was $4000.
All you have to do is have one major motor failure and the iron block is trash. Recently i broke my crank shaft and nearly lost the block. I now have two new main caps and run bearing spacers on the block side of two of the main journals. Years ago i had roller lifter failure. At least that is what we think might have happed first. The iron block was cracked and broken in the cam valley area. When the cam and lifters broke the moving pistons and rods tore the lower block apart also breaking the crank shaft.
Nothing was really salvagable other than the Intake and water pump. I can't remember now, but i think that the distributer was even wasted.
So it's just not the light weight - It's the ability to weld and repair. I will never buy another expensive after market iron block.
All you have to do is have one major motor failure and the iron block is trash. Recently i broke my crank shaft and nearly lost the block. I now have two new main caps and run bearing spacers on the block side of two of the main journals. Years ago i had roller lifter failure. At least that is what we think might have happed first. The iron block was cracked and broken in the cam valley area. When the cam and lifters broke the moving pistons and rods tore the lower block apart also breaking the crank shaft.
Nothing was really salvagable other than the Intake and water pump. I can't remember now, but i think that the distributer was even wasted.
So it's just not the light weight - It's the ability to weld and repair. I will never buy another expensive after market iron block.
Melting Slicks
Joined: Aug 2006
Posts: 3,429
Likes: 20
From: Kingston Ontario
Iron
I just finished porting my 781 oval ports. They're suppose to be good up to around 600hp. There's a lot of hp and savings if you can do the work yourself. Helps to have a buddy at a machine shop. I'm going 2.19 and 1.88 exhaust with narrow stem valves. [IMG]
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Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
There were some interesting posts over on speedtalk were shops had done direct comparisons between iron and aluminum blocks. They found the aluminum block made 30-40 hp LESS than the iron block. Theory is an aluminum block is not rigid enough and looses ring seal at high load.
Tech Contributor
Joined: Jun 2004
Posts: 20,931
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by zwede
There were some interesting posts over on speedtalk were shops had done direct comparisons between iron and aluminum blocks. They found the aluminum block made 30-40 hp LESS than the iron block. Theory is an aluminum block is not rigid enough and looses ring seal at high load.
Instructor
Joined: Sep 2006
Posts: 192
Likes: 0
From: Fort Lauderdale FL
From what I know, the aluminum blocks all use steel cylinder liners, this negates/compensates for the strength differences between iron and alum under combustion, also much easier to maintain and replace the liners on rebuild, no requirement for rebore because the liners take care of this.
Aluminum will run cooler and the weight savings offsets a minor loss in hp if there is one.
About the only negative side to alum is reduced life due to extended heat and cool cycles, eventually the alum will fracture from all of these cycles and weaken, but that's a loooong way off. I have an all alum Jag v12 326 cu in with 120k miles, lots of really hard driving and no issues yet, these engines have a 500k mile life expectancy between rebuilds, so I think you'r safe, the technology has been out for a long time and the overall reliability has proven itself so I wouldn't worry.
Good luck
Aluminum will run cooler and the weight savings offsets a minor loss in hp if there is one.
About the only negative side to alum is reduced life due to extended heat and cool cycles, eventually the alum will fracture from all of these cycles and weaken, but that's a loooong way off. I have an all alum Jag v12 326 cu in with 120k miles, lots of really hard driving and no issues yet, these engines have a 500k mile life expectancy between rebuilds, so I think you'r safe, the technology has been out for a long time and the overall reliability has proven itself so I wouldn't worry.
Good luck
Thread Starter
Burning Brakes
Joined: Mar 2004
Posts: 816
Likes: 1
From: Finland
"horizontal ribs on the side of the block. Not only are they attractive, but they serve to stabilize and reinforce the cylinder walls to the point where engine builders have reported gains of 10-20 horsepower with no changes in combination other than the block."
From here:
http://www.worldcastings.com/prods_pages/86110.htm
From here:
http://www.worldcastings.com/prods_pages/86110.htm
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Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The thicker steel sleeved blocks don't have the problems Zwede was refurring to. The 454 aluminum small blocks DO have this problem because they are right at the maximum bore size. So I would imagine the the 555 - 632 ci aluminum BBC would also have ring seal variations. Or it might also happen in the max bore 454 based BBC 509 ci.
I used to use iron heads. I've also trashed two iron heads that i put way too much money into many years ago. On the flip side - AFR aluminum head, that broke off an intake valve and completely ripped the seat out of chamber. I sent it back to AFR and it came back so perfect and CNC milled that if I did not know which was the repaired one, I could not tell them apart.
I used to use iron heads. I've also trashed two iron heads that i put way too much money into many years ago. On the flip side - AFR aluminum head, that broke off an intake valve and completely ripped the seat out of chamber. I sent it back to AFR and it came back so perfect and CNC milled that if I did not know which was the repaired one, I could not tell them apart.
Last edited by gkull; Nov 21, 2006 at 12:40 PM.
