I have a 454 which I'm going to rebuild. What is the performance potential of casting #336781
620 74 GM9T Pass. From what I understand they are oval port, open chamber (73-84). Can you tell me what they flow, any sizes on runners, how they respond to porting, etc , Thanks.

781's and 049's are the open chamber heads of choice. Port them and clean them up a little, throw in 2.19/1.88 valves and you're good for up to 600 hp or maybe more depending how you build the engine. Specs...336781.....73-85...oval...OPEN...454, 118cc chamber, 256/114cc ports

Bob is right on with his info. unless i was building an all out race car, i'd use 781/049's on any 454, especially if it's heavy street car with pump gas type compression.

No offense meant but I just used the search function and typed in "781" and I found a TON of info! smile.gif

781's are capable of well more than 600 hp. I've got the dyno sheets to prove it. They will support about {according to experts} about 670 normally aspirated horses. However, if your heads need valves, plus the work to open them up, plus a valve job, plus decking {just to clean them up}, plus guides, decent rocker studs, get charged for hot tanking etc, well. Most people on this board know what I'm going to say next. Find some sucker who has done all this work and will let heads go for 600 bucks, or get a weekend job to earn a few more ducats and get some nice cheap aluminum heads. They exist.