Timing retard under boost

do some searches on google. back in the day volvo had a vacuum advance/boost retard diaphragm. if you can find one and retrofit it that might be an option. the 6530 is probably the better way to go though.

my initial timing is 12*, i limited my mechanical to 6* and have the vacuum advance still hooked up to give me 28* total while cruising and 18* on boost. it starts right up and moves out pretty good. i have plans of going the 6530 route when i have the money for it though. a little more timing in certain conditions would help.