Don Terrill’s Speed-Talk

How hard does an aluminum block need to be to work well for high performance use? This is a small block engine making about 600 horsepower from 430cid but not high compression or high RPM with a valvetrain that will last a lot of miles.

When I check the candidate block it checks at about 85 on my Brinell tester is that hard enough? Other blocks I test check out harder, a Ford 4.6 production block checks about 95, a Fontana 105 etc. How hard is hard enough?

check a corvette ZO-6 block as they last at 650 HP. would if the block is sand cast vs die cast make the difference in hardness ??

Is the hardest the best? High silicon Reynolds 390 blocks are extremely hard. Hard apprears to be brittle sometimes.

I'm wondering the same as ptuomov. I don't think hardness necessarily translates to strength or stiffness. I would think tensile strength would be a better gauge?

I think you're right in that the tensile strength would be very important but what I'm wondering about is the block's ability to resist having the lifter bores wear out or the main caps sink into the block.

That is a definite concern, which is why I put bronze bushings in mine. I don't trust the wear properties of the aluminum. I know many have had luck running straight against the aluminum but that is one less thing I have to worry about internally. It's especially important if you are running hydraulic roller lifters that require tight tolerances.

I would think you need both. However you cannot have tensile strength without a specific hardness. A soft block will move even with gyrating forces. This is even evident in cast blocks as you push the hp envelope.Why do block mfgs add cast or material to strengthen these areas. I would think most aftermarket blocks have a higher hardness. Be interesting to know what a new shelby block has.It is interesting that fontana race block is harder.

lAST i KNEW ford mod blocks were supposed to be like T6 material. costing decided to go with case hardening not sure if thats still the norm.