Originally Posted by GUITAR1989
I got my Vortec 350 in my 74 c10. Im just a bit confused on vortec timeing and vacuum advance to be more specific. My truck has a stock L31-R crate long block with an edelbrock 600cfm, Weiand Stealth dual plane, Headers, Dual exhaust, 3.73.
10*initial+20*mechanical is that a good safe starting point for my engines timing? Should it be in by 3000 or is it different since the engines in a heavy truck? I have an adjustable vac can on its way to the local parts store. Vac advance is throwing me off a bit. Im going to run manifold vac. What should my vac advance be limited to? and what should it be reading at idle and part throttle? My engine pulls about 20hg at idle if that matters.
Thanks for reading guys
Vortec heads can use 32-34 degrees total advance (not counting vacuum advance). So you will be safe at 10 degrees initial/20 degrees mechanical. In fact you might find the engine liking slightly more initial, this will depend on the vehicle and use, etc.
The 'all in by
' rpm depends on the load the engine is under. You want the total timing all in as soon as the engine will allow it, w/o any detonation. And in most cases this can be done by 3000 rpm or before. But with a truck being worked hard you might not be able to get all the timing in by 3000 rpm w/o pinging- it depends on weight, load, gearing, fuel quality, cam specs, compression ratio, etc.
I would set it up conservatively at first, then work towards bringing in the mechanical timing sooner by using a lighter spring or springs (the springs can be mixed and matched- they do not have to match on both sides).
The vacuum advance adds about 10-12 degrees. The page cdminter59 linked to has the details.