I finally bought my self an adjustable timing light to set my new vortec heads this spring. I have been reading a lot about them because it seems the vortec heads like a little different timing.

I have ready two different scenarios about timing these heads and I was wondering what people have done and what worked for them

1. Disconnect the vac advance, set bad around 10, get total mechanical at 22-25 around 2500-3000rpm. Reconnect vac and find about 34 degrees total advance.

2. Disconnect the vac advance, set bad around 10, get total mechanical at 34 around 2500-3000rpm. Reconnect vac and find about 45 degrees total advance.

So who has done what and how did it work out for them.

Just a little info, I am running a XE274 cam, patriot 2.02 vortec heads with a 355 and -5cc valve relief pistons for about 10:1 compression.

 

When I had my 98 pickup dyno tuned (stock L31 Vortec heads), it only wanted 29 degrees total timing (base timing table at 25 deg + PE adder of 4 deg) at WOT for best power. We put 93 octane in it and tried more timing, but it made no more power. Stock timing on that vehicle was only 24 degrees.
Take that for what it's worth. We didn't put a timing light on it at WOT of course, but a light on it at idle corresponds within +/- 2 deg of what the PCM tables say it is.

 

I used to run my Vortec/XE274 motor with the distributor locked at about 35* (my timing marks are probably -/+ a degree or two). It ran it's best track times like this and also idled best... With a cam like the XE274 you'll want as much initial timing as possible.

 

With or without extra vacuum?

 

I don't feel anyone with a "performance" type engine should run vacuum advance. The problem is that if you stab the throttle from a cruise the piston will speed up much faster than the distributor's vacuum diaphragm can release the timing. This will more than likely cause detonation that you may never even hear but it'll eventually kill your motor.

 

The vacuum advance does NOT get added into total timing for WOT, because you should have near zero vacuum at WOT.

There is nothing wrong with using a vacuum advance unit on your distributor for a performance application, but it will need to be of the adjustable type, and you may also need to add in a physical limiter to the amount of timing the vacuum advance unit can add.

As for Vortec heads, the normal Vortec heads require only a small amount less total spark advance for best power. Each combo will be different based on several other variables besides the head design, so don't assume a particular timing number goes with a particular head.
It is the swirl-port heads that require significantly less spark advance.

There are some links in my signature with information on setting up timing curves for distributors.

 

Nice I do have adjustable vac advance. When I bought the car it was disconnected but after I connected I noticed it warmed up faster and had much better response at low RPM so I figured I would keep it.

I cannot wait till spring to get he car back out and tuned with the new heads, winter came too fast and I had to stop and put it away before the snow hit.