Farndon Wide vs Narrow Journal

[Rick Iverson]

Gents;

Gathering items to build a 1.6 period correct (circa 1972) FB BDA. I have access to a wide journal crank, but I understand narrow was the period correct choice. By design or by SCCA sanction?

[bob darcey]

Design. The Cosworth BDD crank was narrow journal, 12 bolt. More information at https://www.historicracing.org.uk/pa...specsheet.html

[jstowe]

I built up a BDD from a Cosworth kit in Dec. 1974...by that time, the cams supplied were F1 profile, and the carbs were 48mm. I don't believe that SCCA ever cared whether one used a narrow or wide journal as long as the bore/stroke was correct. That said, I have never heard of anyone using the wide journal crank in a BD, but I doubt that it would hurt.

The instructions from Jack Field (Cosworth's racer's friend if there ever was one.) were to put the piston .005" down the bore at TDC, and index the cams at 102 degrees. Cosworth reported 210 BHP for this spec with 48 mm Webers in their letter to me. Because of the small valve sizes decreed by the F/A rules, the relatively long duration F1 cam profile was not a problem, and these engines had a wide torque band. SCCA never spec'ed a specific cam profile to my knowledge. As I understand it, most vintage organizations still require the original bore/stroke ratio, but now allow larger valves. Go with the big valves and a DA19 cam profile if you want more grunt with good driveability. Many current engines are at a 14-to1 CR because of the improved fuels in use now. Also, the newer round tooth style timing belt and pulleys are better than the original square tooth style. I doubt anyone cares if you make that change either.