mech vs vac advance
Thread Starter
Melting Slicks
Joined: Dec 2000
Posts: 2,130
Likes: 1
From: mesa,az
mech vs vac advance
I am building a little 327 hotrod engine to replace my #s matching one in my 65. i am looking at the ignition right now, i want to keep the tach drive. that leaves me with the originial distributor with a conversion unit. a mallory or MSD mech advance unit, or an MSD vac. advance unit. what are the pros and cons of these choices. I am lost on this one for sure.
thanks
greg
thanks
greg
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Unless it's intended for race only use, stick with a vacuum advance unit. While it won't affect peak power either way, the vacuum advance will give you better drivability (including lower temps in many cases), fuel economy, and convenience. If you decide you don't want it later, you can just unplug it. If you get a non-vacuum advance unit though and decide that you do want it, you get to buy a new distributor.
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,264
If you don't run a vacuum advance that is properly matched to the idle vacuum of the engine, I can just about GUARANTEE you that the engine will run hot or overheat at idle and low speed driving.
You want maximum vacuum advance - about 16 degrees - at 2" less than typical manifold vacuum, and total idle timing should be about 30 degrees, which is the sum of initial, full vacuum, and maybe a few degrees of centrifugal if you have a quick curve that starts below idle speed.
Duke
You want maximum vacuum advance - about 16 degrees - at 2" less than typical manifold vacuum, and total idle timing should be about 30 degrees, which is the sum of initial, full vacuum, and maybe a few degrees of centrifugal if you have a quick curve that starts below idle speed.
Duke
Last edited by SWCDuke; Jul 15, 2004 at 12:32 AM.
