Jump to content

timing specs (help)


Recommended Posts

  • Replies 8
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Z24 with idle at 700 is 3 degrees BTDC +- 2 degrees. Don't forget this is a dual spark plug head and the timing is very much less because of the shortened burn time.


This is a ported vacuum advance so at idle there should be none as the port is well above the throttle plate and reading atmospheric pressure. None of the factory service manuals mention disconnecting the vacuum line to set timing. Although there's no reason to (at proper idle) there is no harm in doing so either. Disconnecting the vacuum advance hose is a hold over from the 50/60s when intake vacuum was used. No, you don't need to plug the disconnected hose either.

  • Like 2
Link to comment

Our modern fuel likes 14 BTDC at idle.  Due to how much timing is in that distributor, the engine will be MUCH happier if you jump it up to 8 at idle.  Factory settings that are more than 20 years old need to be modified to run better with all the additives in today's fuel.  Anti-foaming agents necessary in high fuel pressure engines generally mean you need more initial timing at lower rpms.  I've rebuilt a few of these.  Its perfectly safe.  

  • Like 1
Link to comment

All engines like more timing at idle, however, adding static timing will add to the mechanical when revved up. If the total timing is 34 degrees you are now at 38. These engines are dual plug they don't need that much advance because the fuel burns in less time. In addition, they are almost hemispherical combustion chambers that are very detonation resistant to begin with. It may be pinging and you may not notice it.

  • Like 1
Link to comment

I have run my z24 up in the 10 degree initial timing zone for quite some time. It was set there based on ear and butt dyno then checked with a light later on but left alone.


I'm not stating it's prefect, but it definitely woke up across the entire rpm range.

Link to comment

Never trust factory timing specs.  That distributor should have a 12.5 degree cam in it, so its "14" according to the book, but not in practice.  Double that for crank advance, then add your base timing.  There's easily room to go to 8-12, or even higher which is why I recommended it.  If you have the 9.5 degree cam, then go up to 14-15 BTDC at idle.  I don't give offer up numbers unless they're real and tested - there is liability involved since I do this for a living.  


Then add in CA fuel if you have to deal with that (is that what you have in HI?), and you can add a couple degrees of timing to make up for the extra additives.  Maybe a little less at sea level?  

  • Like 1
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.