the distirbutor im using is a vacuum advance...it says in the manuel that it will advance up to 10 degress at crusiing with 15 lbs of vacuum....

this is the first time ive tried to set up a timing curve...i dont want to detenate my heads apart

 

Generally, you would adjust it until you get ping from too much advance and then back it off until the pinging stops. At that point you would be giving it as much advance as it could handle without pining. The spark curve in the pcm for the LT1 is pretty agressive and it has the knock sensor to back it up in case it needs to retard the timing. Unfortunately, you don't have that sensor to help you out in those situations.

 

so basically i should try got all the spark in before 3 grand, like 2,500-2,800...the distributor comes with the 21 degree bushing installed...even with 10 degrees base id still need more advance...


i appreciate your help bud!

Rob

 

would you happen to have the 6 speed verion of the table?...

 

it it was me... and its not. i would try and run it just like a traditional small block chevy. if you have an adjustable advance can and some springs you're ahead of the game. what i would do is try and get it all in by 3k or so and then set the initial timing about 14 or 15* with the vacuum unhooked and the idle set bellow where the advance starts in. with your 21* mechanical advance you'll end up with 35 or 36* or so total timing before you add vac advance. which is right on for a performance 350 its been done that way for years. leave the vac advance unhooked and do a couple of full throttle runs and check for ping. now the tricky part if you had a unit with a plate to lock out total advance like the crane cams kit then lock out the max possible unless you're running egr then you can back it off a couple notches from max lockout. tighten the part that adjusts rate with an allen key (usually supplied) until its all the way tight and then back it off 9 or 10 turns... it may take more backing off with a stock cam. then make a few part throttle runs but not wot because vac advance isnt in use at wot because manifold vacuum should be 0 or so low that it wont pull any advance.

vac advance has no effect on wot performance just part throttle fuel economy response. once you get your timing set right its time to move on to fuel but if your timing isnt right you'll never figure out your fuel.

the timing in my truck is set on 14 initial and comes in with 34 total but i'm dealing with some larger tires and a heavier load. so i'm not running as much total timing to build in a safety margin.

on another side note most sbc's before the lt1 ran very well with 34-38 deg total timing but its a check and see deal with different elevations climates and motors. and dont forget when setting your timing to make sure your motor is idling low enough that the mech advance isnt coming in at all.

 

I don't, sorry.