Black Jade wrote:

On a 1969 302 which vacuum source is reccomended for the distributor advance, ported like holley says, or manifold?

Ported...jj

So if I switch from ported to manifold my idle should go up immediately. And then readjust timing?

jkordzi wrote:

13james13 wrote:

So if I switch from ported to manifold my idle should go up immediately. And then readjust timing?

Kinda sorta.  I think you start with the your goal for total timing and work back from there.  So recurve your distributor, then set initial timing, then adjust your vacuum advance.
 

Ok thanks, just looking at different options.

Last edited by 13james13 (6/23/2015 5:37 AM)

On my 68 with factory air, the ported vacuum runs to a 'thermal vacuum switch' , then to the distributor. This is so the engine, if left idling, begins to overheat, it switches the ported vacuum to full vacuum which boosts engine speed and increases cooling from the engine's fan. Now, I don't know if the 69 had this feature, but 'thermal vacuum switch' will get you some pictures of it.

I read a lot on this and there is this well known write - up around about this that makes a definitive statement that manifold vacuum is the way to go.  A lot of people think it's gospel and it's quoted everywhere.

I say bull.  Why do you need additional advance at idle?  I don't see any advantage. I did discover a big disadvantage though.

I was having trouble where the car would drop idle speed very quickly,  and even stall if I let it, when idling and turning the steering wheel or pushing the hydroboost brake.  It made for problems when off the gas while braking and turning a corner,  or parking.

Tried a lot of things to fix it, but it was just weird. The problem turned out to be manifold vacuum advance.  Although it seemed like I had a good strong 800 rpm idle in neutral or with the clutch in,  it was what I guess I would term a "weak" idle.  My theory is that timing was so advanced at idle that it couldn't handle any load from the steering pump, because it was firing so early it was fighting itself similar to how too much initial timing makes for hard starts.

I moved to ported timing,  and now the idle doesn't drop at all when steering pump is working.  Not at all.  I can move it back to manifold,  adjust it to 800 and it will stall under steering pump load,  and move it back to ported and reset idle to 800 and it has no problem with steering pump load.  Easily repeatable.

This also might help folks with automatics whose idle drops too much when put in drive.

So,  my vote is ported because manifold is all con and no pro I can figure out.

Bob

Last edited by rbtconsultants (6/24/2015 10:51 PM)