Thrre is no reliable dyno tested power ratings for the 261 except for the article in the May 55 Hot Rod magazine.A stock 261 on a dyno devoloped about 112 net HP at 3600 rpm.The net torque was around 200.A fully modified one,considered borderline streetable then,made just under 200 hp.In the 50 years since that test,nothing has really changed with 235/261 speed equipment as far as maxiumum power is concerned.Even guys who grind cams for these engines,as well as the GMC's don't even know the correct rocker arm ratio.
The only person I know who's seen a modified street 261 or 235 on a dyno is Patrick Dykes.He claims he's never seen a streetable 235 with more than 175 hp or a 261 with more than 200.
Leo Sanducci,who wrote the 292 hop up book ,drag raced 261's before 292's .He told me an all out 261 drag engine with major head work and a 2000 rpm idle makes 280 hp on a good day.And it needs to be reved to a scarey 6500 rpm to get the power.
These are fun engines to mess with however.
