Building a Reliable and Powerful Street Engine

Currently, it is probably a good idea to stay with the VW-rod journal configuration, as opposed to the traditional Porsche 912 diameter or the Chevy 2.00" diameter. Why? It is very difficult to find an affordable, and suitable connecting rod in the Porsche 912 configuration (it had once been the industry standard), and it may prove to be difficult to find connecting rods with the Chevy journal in a suitable length for the 82mm crank in a street sedan. The Chevy rods are commonly available in lengths of 5.700" or longer, too long for this application. A VW-journal rod crank can accept either stock-type VW 311B rods (upgraded by Gene Berg Enterprises or Rimco) or the more popular aftermarket Bugpack/Eagle rods, which are available in 5.352" and 5.500" lengths.

Why different rod lengths? Two reasons: clearance when using a longer stroke crank and crank-to-rod ratios. Longer rods are sometimes utilized to allow the piston skirts to clear the webs of the crank at BDC (bottom dead center). Also, a longer rod may allow the engine builder to find a more suitable rod ratio than the stock VW rod may offer with his/her particular stroker crank. A short 5.352" rod on an 82mm crank will increase piston speed dramatically over the stock VW rod on a 69mm crank. The faster piston speed will actually build cylinder pressure faster (as it "pulls" the intake charge through the inlet pipe harder and faster), increasing mid-range torque, and sometimes engine acceleration. Increased piston speed, however, sometimes leads to side loading of the piston and rings, prematurely wearing the rings (at higher rpm use).

A longer rod, however, will build cylinder pressure later and slower than the shorter rods as the engine accelerates, resulting in a sometimes "lazy" powerband. A 5.700" rod is, in my opinion, too long for a street 2276cc. The 5.352" works great (some piston clearancing may be needed), the stock VW rod (in its upgraded form) works fine (though it requires more clearancing than most aftermarket rods), and the 5.500" rods are probably the best bet for an 82mm VW-journal crank. The 5.352" rod gives a great 1.65 rod ratio on the 82mm crank and the 5.500" gives an even better 1.70 rod ratio on the 82. Why is the 5.700" too long? Not so much because of the 1.77 rod ratio, but more importantly because of the excessively thick cylinder spacers that would be necessary to achieve proper deck height later! With the current reasonable costs of the Bugpack/Eagle forged rods (when compared to modified stock VW rods), I see many advantages to using them for this high-output project.

Next: Part II - To the Camshaft, and Beyond.