Okay, I know it's simple math, but am I understanding this right? With vacuum advance added in, we are going to be running 52 degrees advance above 3000 RPM? That seems like a ton of advance! Just want to make sure I'm getting this right because I'm about to install and time my 383 and don't want to do anything crazy.

 

68vert....... What he's saying is (or read it this way). Take the INITIAL timing number, whatever it is, and add onto it whatever the distributior advance will be. That gets you the total.

The advances in distributors can vary by totally now much they apply, and/or, how fast they come in which is usually by springs or a combination of. So in theory, lets say you set your initial timing to 10degrees BTDC at idle (also with no vacuum advance hooked up if you have it)............ what this means is that if you kept the timing light on the mark, while you increase idle up to 2500-3000rpm you would ultimately see 36degrees because once you start up to a highter rpm your distributor starts to apply advance. (like if you just bilp the throttle at idle, you will see your mark move)

BobR

 

I think a light bulb just came on in the old noggin. Let's see if my revelation is correct. I was thinking that you all were saying to add initial plus mechanical plus vacuum to get an absolute total of 52 degrees. What I now think I'm hearing is that once you set initial, you can get to the 36 degree final either through mechanical or vacuum depending upon if it is load induced or RPM induced. Do I have it now?

 

Not really - essentially, you set everything up to obtain the desired TOTAL at the desired RPM and ACCEPT the initial timing that you are left with - UNLESS - it is WAY out, then you need to recurve.

 

That's correct. You got it.
You end up with a total mechanical advance (without vacuum advance) at elevated rpm of 36 degrees. Then you add about 18 degrees of vacuum advance on top of that for a total combined maximum possible timing advance of 52-54 degrees. That's correct.

Here are my personal preference timing specs as I have them published in my "how to set timing" paper:

· 36 degrees total timing (vacuum advance hose disconnected), all “in” by 2500 rpm
· 18 degrees initial timing at idle (vacuum advance hose disconnected). Note that it may not be possible to achieve the 18-degree initial spec with the 36-degree total without modifying the distributor advance stop system. It is more important to achieve the 36 total than to hit an exact 18 initial. However, if your initial timing is very low (below 12 degrees) with the 36 total, it is important that you repair or modify your distributor in order to achieve correct engine performance
· 16 degree vacuum advance control unit with a pull-in spec that allows the full range of vacuum advance to be pulled in at the engine’s idle manifold vacuum level. Connect to manifold vacuum for most applications (this will allow the engine to idle with actual timing at idle of 34 degrees).

 

i thought i read in a post on this forum somewhere that if your timing advanced beyond about 36 degrees you would get detonation if you are not running premium gas....

is that not correct?

educate me please, someone....