shelby 427 aluminum blocks

[PJ10]

Thanks for your input. As a couple of you have pointed out, the laws of physics would imply that the tapets are loose when cold and tighten up (less clearance) when at operating temperature. I believe this is why some put in hydraulic lifters instead of using solid. They take up the cold 'slack'. Bad thing with hydraulics though, they will float long before solids! There is quite a valve 'slap' when cold with solids in an aluminum block. HP is being lost and wear is introduced over time.

I read that this is why HM (Holman Moody) prefers cast blocks. Their cast blocks (FORD Blueprinted) should be in production in the fall.

[Cobra #3170]

It's the other way around, the block grows more than the push rods therefore valve lash increases with temperature IE the head moves away from the crank as the deck goes up from thermal expansion. The push rods are steel and their thermal rate of expansion is much lower so they stay about the same length and clearance between the rocker and push rod increases.

[Suomien]

So if you want an alloy block, your best bet is to get a set of the new alloy SOHC heads and do away with pushrods.

You would want a chain tensioner (or belt drive).

Problems solved.

Aluminum pushrods? What diameter would be required to match the stiffness of steel? If no overall difference in weight due to increased diameters, why not?

[bret a ewing]

Originally Posted by PJ10

Thanks for your input. As a couple of you have pointed out, the laws of physics would imply that the tapets are loose when cold and tighten up (less clearance) when at operating temperature. I believe this is why some put in hydraulic lifters instead of using solid. They take up the cold 'slack'. Bad thing with hydraulics though, they will float long before solids! There is quite a valve 'slap' when cold with solids in an aluminum block. HP is being lost and wear is introduced over time.

I read that this is why HM (Holman Moody) prefers cast blocks. Their cast blocks (FORD Blueprinted) should be in production in the fall.

PJ10,

Funny thing, I was at Daytona International last weekend for the historic races and talked with a guy who is associated with Hollman Moody. He had a GT40 MKII there. He states the Shelby alum. block uses "inferior aluminum" in its casting process. He states this leads to uneven expansion of block and heads causing gasket failure.
I blew a gasket last year after about 1800 miles and 3 years. According to Keith Craft this was do to defective Fel-Pro gaskets. He sent me new ones and its holding up good so far. Currently has 2200 miles -w- around 1 1/2 hours agressive open track time.


Best, Bret.