Quote:
.. but i honestly could not tell a diffference in off idle or light throttle cruising power at all, in fact i made a run on manifold vaccume around my block and on ported vaccume and i swear it was running better on ported vaccume
The reason it seemed the same under those circumstances is because it essentially was. The vacuum from ported and the vacuum from manifold become indistinguishable as the throttle opens.
At idle, in neutral (or Park) there is very little load. Therefore the engine only needs to overcome the internal friction. So you could advance the heck out of it and get away with it. But as you found, the improvement was an illusion. The real test at idle is in D for automatics and with the alternator loaded (lights & fan on). If the engine still is fine with a relatively leaner mix, then using manifold vacuum to advance the timing may be a good match. If the engine prefers a richer mix, then additional advance is probably hurtful and ported is likely to work better.
For stock and close even modified engines, the typical factory protocol is the way to go. Usually it involves plugging the vacuum line to the distributor (golf tee is a favorite). Set the timing and idle mix at a given rpm (in D for autos). Check the mechanical advance. Then reconnect the vacuum lines and check the timing at given rpm. For non-stock engines of course the are no specs so you have to develop your own baseline.
As described in my first post (and link) which way to set up an engine depends on the engine.
Last edited by Mattax; 03/19/12 04:13 PM.
