[nightwrencher]

a number of years ago, I did a junkyard build up bolting on a set of '70 "13" heads on a '74 400 block. about a week after break in, and "looking for a carb problem" it dropped a valve and chewed a piston. they were manley 8000rpm one-piece racing valves, shaft of valve was not bent at all. I never got anything from manley, some of their tech guys said,"they have seen the piston slap the valve and not bend the shaft but drop the head.
one time I did read on some piston man. site that you need a specific valve relief, or in their case, piston for "13" heads. Is their any truth to this? if so, what do you need.
right now I got a built '72 400 I bought as a longblock from a machine shop with "11" heads, ported and polished, supposedly machined and fitted with 2.11/1.77's though I never verified. after I get to do some amateure racing for a couple years on my current combo, I am thinking of building a 461 with the old block since it wasn't damaged. I got these fresh 13's just sitting there and wonder if they would be a good canidate for the stroker. would I need a certain piston for this? then again I may swap them on my current combo or sell them in favor of e-heads. any suggestions?
another "fact or fable" I see a lot of people reference them as RAIII heads, is this true, If I decide to sell them or show off my engine (lol) I don't want to mislead someone.

[Herb Hagan]

Nothing different I'm aware of, other than larger CC's (78) than what they are listed at (72). I run 13's with .650" lift solid roller and standard 2 relief Ross pistons.

Edit: More cam info
286 @ .050" .433" lobe lift (.650" @ 1.5 ratio/.715" @ 1.65 ratio) 106 CL

Herb

[Skip Fix]

I'd expect more a valve keeper failure than incorrect vavle pocket.

[buwalda]

The #13 heads are the 75cc variety & the valve head is closer to the deck than the later big chamber/low compression heads. So if the block/heads were decked, coupled with a long duration cam, it is quite possible that the valve & piston had a coming together at a higher rpm. Other variables that increase the risk are narrow LSA, high ratio rockers, etc. You didn't give any cam info, so hard to be more precise.

[nightwrencher]

it was a comp cam bracket master II. 230/230 I believe. stock rockers. It may have been trw, I don't remember, but back when carcraft or hotrod had the "build your dream engine" contest, I remember seeing on one of the piston websites spefically singling out the "13" heads in a notation as needing a diff pn.
anyway, what about the performance on these heads, and are they true RAIII's. I probably won't be able to afford e-heads on next build or modification so will probably use these.