The aftermarket rods are nice, but at the moderate power levels we are seeing the expense might not be warranted. Aftermarket rods are generally lighter and that'd be a nice benefit if you are looking for every last scrap of power or if you are into having talking points about your build.
All 951 rods are fine, forged or the later (possibly sintered, possibly forged but a different design) rods. The early forged 944 rods are good too (and might in fact be the same rod as the late 951 rod.) The stronger 968 2R rods are probably fine too but I am unaware of any high HP builds on them. I do not know how strong the 944S2 rods are but as they are not common I would not bother with them. The 1989 944NA 2.7L might use the same rod as the S2, but you don't want any 944NA rod other than the early forged rods so ignore those as well.
The debate rages on as to what rods ended up in what engines. The common wisdom was that the forged 951 rods were only found in the 1986 engines but have been reported in later 951 engines as recent as 1989. Part numbers suggest the late 951 rod is the strong early 944 forged rod.
The story also goes that the forged 944 rod only came in 1983 and some 1984 engines but I got a set out of an 86. Some say the changeover actually came in or after 1986. These early forged 944 rods are generally quite inexpensive used, I think the set I pointed out as being FS on Pelican were $75 including pistons. They are nice. Some say the 951 rods are better though. I have no idea. Some feel the 'RARST' part number suffix only appears on forged rods but I think that might not be true. The part number should tell you if you have something good or not.
My understanding of the part numbers follows:
Early 944 rod - 944.103.101.3 RARST
Early 944 Turbo - 944.103.110.0 RARST (some say these are the best.)
Late 944 Turbo - 944.103.101.3 (or 3R or 3RARST)
[The late turbo (cast, sintered or forged depending on who you ask) rod seems to have the same part number as the early 944 forged rod.]
Cast 944 rods, unsuitable for higher HP applications:
944.103.001.0
944.103.008.0
Part numbers ending in 1R or 1RARST I suggest avoiding.
Used rods should be checked for cracks and straightness and roundness of the big end.
Get new rod bolts and nuts. GET NEW RODS BOLTS AND NUTS.
q: Should I replace the rod bolts and get new nuts? a: Yes.
If you are just doing rod bearings you can probably get away with only replacing the rod nuts but with used rods you have no idea how many cycles the bolts have seen. They might be good for one more stretch, or they might decide to pop. Think of rod and main bolts as really stiff brittle springs that you stretch to hold your assembly together. You hold it by stretching the bolt just enough to really clamp the assembly together but not stretching it to the point the bolt gets weak or breaks. Sometimes when you torque one of these it will suddenly get easier to turn and the torque will drop or level off. That means the fastener has gotten weak and is ruined. It'll break in a second. Instead of cursing your luck in this case, thank the fastener for letting you know it needed to be replaced instead of snapping at 7k RPMs.
What I think might be better advice for a street engine is to just run what you got and see how it goes. A lot of stuff can go wrong in a rebuild. Your engine was built by highly trained professionals in a very clean environment and has worked for many years afterward. Why spend the money to possibly end up with an engine that is not as well screwed together? To replace a rod that might never bend or break? Tough call. If you are going racing, then yeah spend the money. Race weekends are expensive.
-Joel.
