just an update, it`s been a hard two years trying to sort out this comb(0.080 over bore /318 valves ported head/.556lift/ 256@0.050 degs cam and 750cfm mech holley/4-71 blower/slantsix) i started a thread awhile ago about using 2 650cfms on this comb,it seem that it wasn`t the problem behind my head gasket failures, after talking the problem through this site and the slantsix site i couldn`t get a handle on why i kept blowing the head gasket on #1&#6.it seemed to be lean on top end because it only happen in third gear on top end of the track. i pulled the 2/650 and replaced them with 2/600 cfms that were boost referenced,thinking that if my problem was caused by being over carbed the vac seconderies would only give me what i needed and not lean the motor out due to lack of flow, no luck, so then i tried just a single 750cfm that i ran on this comb with a smaller 4-53 blower,ever though the smaller blower developed 5lbs of boost just like the 4-71 that i am trying now it never hurt head gaskets,well it still blew the gasket but only on #1cyl, so out of disperation i had an old steel shim head gasket that i spraied with gasket adhersive/sealer and put 90ftlbs on the head stud(+5lbs just for insurance)and at the last weekend of racing the engine stayed together,starting with a super rich mix i ran a 12.49et/106mph by the end of tha day the car reached a 11.85et/111.65mph, finially got into the 11`set so now i have to wait untill next season to try the 2/650`s or the 2/600`s because the car did 60ft & 1/8mile better with the 2 carbs than with one.i just want to thank everyone who gave me some imput as where to look to get me into the 11`set with my car,thank again terry.