The header has 1.75" tubing and it doesn't help much to go larger because the exhaust ports can't be made very large. That is one reason the split duration and lift cam that I used is a popular choice for big Type 4 builds.
Web Cam Type 4 Camshaft, 86B/86C Grind, 00-662 is designed for Type 4 engines, and it's specs are (In/Ex) .500/.507" Valve Lift with stock 1.3:1 Rockers, 300/310 degrees of advertised duration, and 260/272 degrees of duration at .050". This is an outstanding Type 4 camshaft, longer exhaust duration to aid with the pitiful Type 4 exhaust port! This has a fantastic midrange and top end, and is one of Web Cams best Type 4 grinds for big engines, with a powerband from 3500 to 7000 RPMs, the more headwork and carburetion the better the top end will be.
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