How's my timing?

[minifridge1138]

Hey everyone,

I've done some work on my car lately and hope to get some opinions.

Here are the timing numbers on my car:
Initial: 10*
Idle (initial+vacuum): 26*
Initial+vacuum+centrifugal at 2k RPM: 36*

For the initial+vacuum+centrifugal I had the timing gun dialed to 36*, but the timing mark was erratic and bouncing around by about 10*. Does this mean my centrifugal advance needs to be rebuilt? I know there should be some play, but 10* sounds like a lot.

I was afraid to go much about 2000 RPM because the engine got really loud. What RPM should i hit to map the centrifugal advance?

Thanks everyone!

 

[JohnZ]

When you map your total timing, you do it with the vacuum advance disconnected, as the vacuum advance disappears when you put your foot in it; vacuum advance is only active at idle and steady part-throttle cruise.

Your initial and initial + vacuum numbers look fine. Disconnect (and plug) the vacuum advance hose, and rev it up with the timing light in place until it stops advancing; you should see 34*-36* at that point, but no more. What you're seeing there is initial + centrifugal, which is "total timing".

 

[Vette79]

With the addition of heads, cam, intake and carb; will that throw off the timing? I'm guessing it will and what should the timing be and how do I dial it in using a timing light?

 

[JohnZ]

With the addition of heads, cam, intake and carb; will that throw off the timing? I'm guessing it will and what should the timing be and how do I dial it in using a timing light?

Timing is independent of all those hardware items - it's all in the distributor. For most stock and mildly-modified engines, the following makes a solid baseline with good performance and a good kickoff point for tuning:

Initial Advance (vac advance disconnected and plugged): 10*-14* BTDC

Centrifugal Advance: 20*-24*, all in by 2800-3000 rpm

Total Timing (Initial plus centrifugal): 34*-36* (don't exceed 36*)

Vacuum Advance: Can selected should be connected to full manifold vacuum (NOT "ported" vacuum), and should be fully-deployed at normal idle so it's against its stop and provides a full 15* of advance at at least 2" Hg. less than normal idle vacuum.

If you'll go to this site:

http://lbfun.com/Corvette/Tech/vettetech.html

And download these two articles I published in "Corvette Enthusiast" magazine:

Timing 101

Mapping Advance

It'll take you through understanding the basics of ignition timing and advance systems, and will show you how to "map" what you have and how to alter it for improved performance, using ordinary tune-up tools.

 

[minifridge1138]

Follow JohnZ's article.
Pretty much everything i know about timing came from him and that article.

If you have any questions after you read it, post them and we'll help you.

Good luck and have fun!

 

[Vette79]

After switching vacuum to manifold, didn't you have to change out the weights for proper advance?

 

[petes74ttop]

I tried the accel kit, the weights in there kit were 17 grams each, the original were 18 grams, seems like the springs matter more than the weights. PG.

 

[Vette79]

Think I will leave well enough alone. It all works fine as stock. Make sure timing is correct after the build and be "good2go".