i have a 511 bbc chevy and i turn it close to 7,000...i now have a shorter tire and it should turn 7,200......you can feel the power difference from 6800 up thru 7200...very noticable difference.
also for the record i have an aluminum dovanvan block 632 with Pontiac Big Chief 14 degree heads 822 roller....it made 1200hp at 7600 rpm...and i will turn that motor every bit of that.
Just my opinion on your valve breaking and where you broke it...i think its just the attrition of parts breaking down over time..if i am correct i think you said the motor was 4 years old...thats a long time on the same parts ( in my opinion)..i do not know how much it was run but if you ran every weekend for 2 seasons you got a lot of use out of that motor. here in the South you can run year around...all 12 months on Saturday or Sunday and 9 months Thursday,Saturday,Sunday....so its possible to put FREAKY HEAP load of passes on a motor here in S.C. in a single season..if you show up each time..
Metal WILL wear out and break...IN MY OPINION..i do not think it was your fault or your engine builders..the fact of it is run one long enough and its going to give somewhere.....
thanks Brian
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "