For the most part, the connecting rod bearings looked fine when we disassembled the motor. Other than one or two uneaven wear marks on one or two of the bearings, they all looked like they were in good shape. As I would find out a year later, the uneven bearing wear would be addressed when we assembled the bottom end. (That will be the subject of another update.) I thought everything was in decent shape, so I was taken a bit by surprise when Federico (RD Sport) pulled me aside to tell me that Carrillo wanted to redesign the connecting rods. The complete set of disassembly pictures and pictures of all bearings from multiple angles can be seen here.
BMW M3 Motor Tear Down - Robert & Mary Ann Collins
The problem with the connecting rods
When Federico pulled me aside, he told me that he had sent one of my connecting rods back to Carrillo for analysis. After inspection, he said Carrillo hadn't designed the connecting rods for a boosted motor, and wouldn't warranty the connecting rods if I continued to use them. If was my choice, and I could continue to use my existing set of connecting rods and might not have any problems, or take Carrillo's advice and redesign them, spend another few thousand $$$, and wait another eight weeks. To me it was an easy decision: we must redesign the connecting rods to be safe.
Federico and Carrillo had seen something in the connecting rods bearings so small that I never saw it. On three or four of the connecting rods, precisely where the connecting rod cap bolts together, three or four of the bearings were worn to the copper. At such high power and high rotational velocity (high RPMs), the connecting rod cap was deforming, becoming oval shape, and pinching the connecting rod bearings. Pinching the bearings was causing them wear down to the copper in this location. When I inspected the bearings, I didn't even notice it because it's a very small area -- about 1mm width. The pictures below show the wear near the bearing caps.
The new connecting rods
Once the new connecting rods arrived, I was very eager to see what had changed. I opened the box, removed a connecting rod, then stared at it for a few minutes because I didn't see any difference. Only when I placed the rods side-by-side did I begin to see the difference. Precisely at the spot where the connecting rod cap bolts together, there is a little extra metal. That's about all I noticed. However at the 2011 SEMA show in Las Vegas, I happened to be talking to a guy in the Carrillo booth. I described my project to him and how Carrillo redesigned the connecting rod. Just by coincidence, I was talking to the guy who actually designed my connecting rods and he remembered the project very well. Not only did he add a little more metal at the junction, but he thickened the H-Beam a little, changed the H-Beam radius, and slightly modified by bore size for the connecting rod bearing.
All of these latter changes aren't really noticeable to the naked eye, but you can definitely see the extra metal in the new rods when you compare them to the older ones. A complete picture set of all of the new connecting rods can be seen here:
New Connecting Rods - Robert & Mary Ann Collins
Calculating Rod and Piston Velocity
While I was waiting on the connecting rods to arrive, it seems that I had a little extra time on my hands. So I decided to see how the stock connecting rod compares to the RD Sport RS-46 connecting rod (they are not the same length). So I wrote a spreadsheet and compared rod length, piston velocity, piston acceleration, and rod angle. Since I had specs for the factory S65B40 (OEM Motor), S65B44 (GTS Motor), and RS-46, I decided to compare all three.
I apologize that I don't remember the units of measure when I did this (it was a long time ago). But from these graphs, it's pretty easy to see how each one compares against each other.