Quote:
Originally Posted by Tom Kirkham
Here is a link to my other post:
http://clubcobra.com/forums/showthread.php?t=97890
Something to consider is most of us are not running vacuum advance. So our cars are typically cruising down the road with the ignition retarded from optimum. This means wasted fuel, poorer throttle response and higher under hood temperatures. In a light car with a manual transmission, a SMART driver, and a start retard a good case can be made for looking out the advance. |
I agree, although maybe not locking out the advance. I had a slipped balancer plus a non-vacuum dist which had mech adavncve already partlky in place at idle (bad idea, but helps with cranking). After many years of good performance, I got tinkering with the timing. Bad idea...I wound up breaking a piston by detonation. I can't hear pinging with the sidepipes being so loud, but I could tell it was fighting higher rpms.
So....I jsut finsihed getting my timing set where it seems to be fine again, and those figures are:
23 Deg @ zero rpm
28 Deg at 800 rpm idle
38 Deg max advance
For my cam in the 290 region (I forget the exact spec, but it's a Crane Fireball solid lifter cam), an initial timing should be 14-16 BTDC. But it runs hot there, plus it gave me a bog for some reason. Best idle (highest vacuum and rpm) was at 38 Deg (just co-incidence it's the same number as max advance), but leaving it at 38 at an idle would surely mean knocking once the throttle was opened.
I think max advance is well known not to exceed 38, but again, that is for max power, so I'll see how it runs at highway cruising speed.
I am of the opnion that if an engine needs a ton of advance with no-load, and very little advance under full load, then a vacuum advance would be a terrific help. And since I don't have one yet, my car benifits from timing somewhere in-between. After all, I only give it from 1/3 to 1/2 throttle when taking off.