Bigger valves for 781 ovals
 

Is the original gm hardened seat enough for the exhaust? and if so, what size valve can be used keeping the seat hardened.
Some say you need to use additives with these old heads, and some say it is bull$$.

Need more about your build. NA / SC / HP. Not going to gain much unless you spend more on porting etc than new heads. JMO

NA 502 cid, hopefully somewhere between 550-600hp. Making 520hp now @5300rpm with ported peanut heads via stock size 2.06/1.72 valves, 230/236, 0.620" lift, 112 lsa hyd roller. Going to keep the same camshaft.

What casting number on the heads?

5/16” pushrods?

Stock valves?

equals disaster but considering that’s not your question I won’t go there. However valves and seats are crucial regardless of additives etc. I know making the power with your heads isn’t a big deal but making it last is. If heads been ported im assuming they’ve been flowed? You’re about peaked out with rpm and “definitely” with lift.

Please provide casting number on heads. A little bit confusing when referring to 781’s and peanut port heads. Entirely different. Just sayin

Current heads are 360 casting peanut heads with 2.06/1.72 ferrea 5000 series valves, these heads have exhaust seat insert from the factory. Considering to replace the peanuts with 781 casting, but i quess the gains are minimal without stepping up in valve size, atleast in the intake side. 360 castings flowed around 280cfm @ intake, 205 cfm exhaust without pipe and the port it self is barely ported, just slightly radiused short turn, most of the gains came from chamber work and the valve/seat. I think i could make the 781 exhaust better than the current 360 with the same 1.72" valve, if truly port it. From my understanding 300cfm intake flow should be easy with bigger valve and some porting. The cam has 6 degree split so it might stil work without massive exhaus flow gains, maybe.

The flow ratio is decent for GM heads. I remember GM heads always liked a bigger split (10-12 deg + -) due to the poor exh etc. If you have a good reliable package I’d call it a day unless you go aftermarket otherwise your gain going to be so minimal I wouldn’t think would be worth all the time, effort and expense. JMO of course.

These 781 i have has fresh mint condition bronze quide liners, so installing seat inserts for the exhaust would not broke the Bank, but in other hand i can get 290cc flotek ovals 1500$ pair and go from there. Wonder what kind of power those floteks would make with my cam and what rpm? Quess some where in 5600rpm, that might be over the limit of the gm dogbone hyd lifter.

I wouldn't spend any money on an old set of GM oval ports trying to make power. The aftermarket stuff is so far superior that it just doesn't make sense .

You are right! I just need to take a account my hole combination of parts. The gm roller lifters might be a problem at higher rpms with max recomended spring pressures 140/380lbs , 230/236 @ 050" cam might pull quite high with good set of heads.

I have ran the dogbone lifters with 450# over the nose at .635 lift at 7000 rpm in a boat engine with no ill effects.