Tuning question!

[mikep]

which pump did you end up going with? It sounds like you need to work on your advance curve though. If you had 12 degrees at idle and 55 at full advance then you have 43 degrees total. That doesnt sound like any mallory distributor I have ever seen. Usually they keep them in the mid 20's range. What model is it? For optimum performance you want more like 20 degrees at idle and 36-38 degrees full which is only an 18 degree or so spread although you may be able to get by with upwards of 42 degrees total timing if yours is the typical 8:1 compression late model 454 . A lot more advance at idle will take care of a lot of slugishness problems especially on lower compression motors . If I were you I'd disconnect the vacuum advance for now and shoot for around 38-40 degrees at full advance using the mechanical advance alone. Put the mallory springs back in it.