i never got a chance to play around with the vacuum advance much. i had an adjustable crane can on it and i had it setup for the 305 in the car prior to the 400.
Unfortunately, i lost the cam in the 400 after about 5 miles. it was comp xe268. about half the lifters went concave. i was pretty pissed since i put basically all the money i earned with my summer job last summer into buying the complete 30k mile motor and doing heads for it, cam, intake, carb, noisy gear drive, high pressure melling oil pump, aluminum water pump, etc. altogether i had about 2000 into the drivetrain.
now im about to take it out (as soon as im home from college for the summer) and drop in a 71 350 for the time being.
ive been reading a lot of articles on excessive flat tappet cam failures as of recently. theres been lots of things contributing to this. i think i had problems with the break in because i used stiff springs that came on the heads, comp cams red lube that came with the cam didnt stick well at all and kind of just ran off the cam (next time im using moly lube or comp cams special lube) i did have the valve adjustment right but i also used cheap oil and now that ive read some articles i realize that flat tappet cams need high zinc content which almost no motor oils have anymore because all new cars have roller cams. ive also heard about comp cams having quality control problems and having a high amount of soft cores. also some lifters are from overseas and are not well made.
either way i now have to disassemble the 400 and see the extent of the damage. i also managed to break a pushrod which was probably due to a backfire from the failing cam and the unforgivingness of the gear drive on pushrods (read that gear drives add up to 70% more stress on pushrods). i will keep posted my progress after i get home from school and start work on the car again.
thanks for the help, i have spent a lot of time playing with carb adjustment and vacuum and mechanical advance and managed to get a very strong running 305. i will now see what i can do with a puny vavle (1.72 intake) 350.