I just installed a unilit distribuator in my 70 chevelle 454. we set base timing at 10 degrees. we hooked up the vacumm line and have 40 degrees of timing now.i know it is too high but dont know what it should be. i have no idea who or what went into my motor. also the vacumm line goes on the holley 3310 carb on the upper vacumm port. i hope to adjust the vacumm advance but need to know if the hose is connected to the right port and to know how much vacumm advance should be. thanks gary

Gary,if your running a any kind of aftermarket non stock gm cam 10 deg intial is too retartded .

Heres a good starting place to dial in a mild to fairly hot setup in a 454.

Get a vac advance that has 10-12 deg max advance when fully activated.

Run approx 16-18 deg btdc intial for a total (total = Initial + mech advance in dist)of 36-38 deg btdc. Have motor idling low like 600-650 rpms & vac adv hose unhooked & plugged when setting the initiaql timing.

Then with the vacumm advance you should have approx 48-50 deg btdc timing at light load part throttle cruise rpm which is good for a street perf bbc.

If your total goes over 38 deg with 18 deg initial then you will have to pull the dist to have the mech adv limited/recurved to a max of 20 deg to get a 38 deg total with 18 initial(18 initial + 20 deg mech adv = 38 deg total). You should also have a vac adv installed with 10-12 deg additional adv while your at it.

If your running a very mild cam run the vac adv hose to ported vacuum where thete is no vacuum at idle,just activates off idle.

But if your cam is much above 230 deg int dur @ .05 in your 454 i would try running run it off the full vacuum at idle port so the additional timing at idle will help the motor idle better. But this may not work as well as the ported vacuum so trial and error is the name of the game for this dialing in stuff.

Be aware that if you use the full vacuum port for vac adv hose then make sure to get a vac adv thats rated a min of 2-3 inches below your motors lowest idle vacuum when its fully activated to aviod an unstable/osilating up/down idle situation.

Scott