I forwarded this issue to my brother for his opinion;
Hi Dwaine,
The only aluminum rod that I would recommend for this application is the Bill Miller forged rod for the 2.100" rod journal. Most aluminum rods are built .010" shorter than their steel counterparts to allow installation in common deck height blocks, like if your block was setup at 9.000" (typical SBC after square decking) you wouldn't have to resort to "thick" head gaskets. The piston to head quench pad clearance must be .055" (for this application) or more to allow for the stretch and thermal expansion. I have built engines for sprint cars and street cars with the Miller rods with a great deal of success, and of course drag engines - how about a 468cid BBC with a 8200 RPM shift point equipped with Miller rods that still was in operation after 450 passes? The "New" generation of aluminum rods are CNC carved out of billet flat stock (not forged) that does not have controlled grain flow around the big and small ends of the rod and doesn't have proper
grain flow in the beam area either. The CNC rods can be built by anybody with a CNC mill (I've even built titanium rods on my manual mill for bike engines), so there are some fair designs and some really poor designs out there, and they look so damn good because of the infatuation with smooth, totally machined aluminum - the looks are deceiving! Most of the CNC rods are very squared off and bulky, probably to overcome the design flaw of CNC machining flat stock. The original 7075 Manley rod is forged but not to the standards that I go by. Be aware that all of these rods have the thermal expansion related dimensional changes that effect clearances from cold start to hot operating conditions, the clearances of interest are the rod bearing clearance and pin clearance. The rod bearing on the Millers (and all that others that I've been around) have the rod bearing lower half dowel pinned (bearing is drilled with locating hole) to determine bearing location
fore and aft and to prevent rotation. The big end is fairly massive on any aluminum rod to achieve enough ultimate strength to prevent deformation and failure, this mass expands as a result of the large amount of molecules interacting - so this area grows quite abit, even at an oil temp of 240deg it increases the big end bore enough to allow the rod bearing to "float" in the bore. Upon teardown of a properly built engine you can witness the "bearing float" by inspecting the backside of the bearing - they get burnished by this movement. The engines still run and don't scatter even with this movement, I think its really pretty slight but worth mentioning in this discussion. I normally don't use aluminum rods unless the application will have peak power over about 8000 RPM, even this decision can be effected by component weight and other considerations. So, to answer this guys question, I wouldn't use any aluminum rod other than Bill Millers (which has the
name forged into the rod) for a circle track engine - if they're not Millers install quality steel rods.
Hope your Christmas was good, we had a great time with family,
Any questions on this topic, feel free to ask! Dennis B