Frank McGurk Article in May 1955 HRM; tested a Corvette Six Exhaust Manifold In the famous Frank McGurk test in 1955 on a 261, the Corvete six manifold, with separated pipes and mufflers, increased the torque (and HP) by over 4% at 2000 rpm and by nearly 9% at 4500 rpm. I had one one my 1951 Chevy and another on my 1953, each with a 261. Souded great with glasspacks, good with stock mufflers. With a jobber's discount, they cost about $18 each at the local Chevy dealer in 1956. I saw one go for over $300 on ebay.
