I can't lay my hands on dyno results for a 235, but in the
May 1955 HRM article about Frank McGurk's dyno test on a 261 , he measured about a 5% improvement in peak torque and horsepower by installing a Corvette six exhaust manifold on an otherwise stock 261. The improvement on a 235 might be slightly less. As I recall, another HRM article in 1953 reported about a 3% improvement in peak HP by installing a split manifold on a 216 with dual carbs and some other mods.
Hoyt
