Boosting performance in a vintage six

February 1, 2016 | By Staff

Question:

I read an article in an old issue of Auto Restorer where you said you were able to run a Chevrolet 235 six-cylinder engine at 5000 rpm in your 1958 Chevrolet Pickup without problems. How were you able to do that?

Answer:

To do so safely I used a carefully balanced crankshaft, rods, pistons, flywheel and clutch, and a Doug Fischer harmonic balancer, which unfortunately is no longer available. However, there are services that will build a high-performance vibration damper for your engine.

Balanced rotating assembly — If you are building a high-revving engine it is critical that all of its rotating assembly be balanced.

Plugs added to a light crankshaft counter balance weight. — If a crankshaft counter balance weight is too light, weight can be added in the form of plugs.

Drilled crank to reduce weight. — If your crank proves to be too heavy; it can be drilled to reduce weight.

I also cleaned up the sharp edges and shot peened the connecting rods and crankshaft. If you build it carefully, 5000 rpm is not beyond the engine’s capability, but I wouldn’t push an old Stovebolt much beyond that. Years ago at Clifford Engineering I saw what was left of a 235 that kissed 7000 rpm briefly on a dyno, which tells me that 5000 rpm is not near the breaking point if the engine is built correctly.