YOu run into too much initial timing issues if your distributor total advance is not enough, and you have to give it more intial advance to get the top end where you need it. That's why the distributors need to be tweaked so you get quick response, easy advance at idle, and more at higher rpms as needed. Many big cams change the vacuum signal too, it could be too weak at idle or off-idle to operate a stock vacuum canister. I often go to a fully mechanical distributor in high performance engines, and get rid of vacuum altogether. Sometimes I get my hands on adjustable vacuum canisters, which helps tweak it to match the engine. You can adjust total advance from the vacuum canister, and by swapping springs you can adjust the sensitivity. Same with the centrifugal weights. Many guys opt for the easy and cheap route and just drop in an aftermarket dizzy and leave it as is. And then wonder why the engine falls on its face when they try to drive nicely
Race engines don't need to pull strong from idle though...
