Ported Vs. Manifold Source: Vacuum Advance

[RickT]

Where's the best place on the manifold to tap in? Mine vacuum is connected to the carb. and the only port on the manifold is where the brake booster ect. is connected.

 

[Vette79]

Where's the best place on the manifold to tap in? Mine vacuum is connected to the carb. and the only port on the manifold is where the brake booster ect. is connected.

Connect your vacuum advance to a tree fitting on the intake manifold just behind the carb. Then re-adjust timing. I had to purchase a different fitting to accomodate the vacuum advance.

 

[baxsom]

Connect your vacuum advance to a tree fitting on the intake manifold just behind the carb. Then re-adjust timing. I had to purchase a different fitting to accomodate the vacuum advance.

just a little confused. why would you readjust the timing after you attached the vacuum line to the distributer.

i thought you got your base timing with the hose disconnected and then plugged in the distributer. with full vacuum this will increase your timing now. which i thought was the point here.

 

[Vette79]

Read these articles by JohnZ. Look under Timing and Vacuum Advance.

vettetech

 

[baxsom]

yes i have read those articles numerous times and that is why your post confuses me. your post seems to contradict the article.

to me you are saying that once you have your base timing set
ie 36 degrees mechanical advance at 2500 rpms (per the referenced site)

to attach your vacuum source and then readjust the timing.

why would you readjust it when the extra advance from the manifold vacuum is what you want.

it seems to me after reading the article (over and over again)
that you set the mechanical at 2500 rpms. then hook your vacuum advance up to a full vacuum source. then you are done. no readjustment necessary UNLESS you are getting knock.

 

[Vette79]

yes i have read those articles numerous times and that is why your post confuses me. your post seems to contradict the article.

to me you are saying that once you have your base timing set
ie 36 degrees mechanical advance at 2500 rpms (per the referenced site)

to attach your vacuum source and then readjust the timing.

why would you readjust it when the extra advance from the manifold vacuum is what you want.

it seems to me after reading the article (over and over again)
that you set the mechanical at 2500 rpms. then hook your vacuum advance up to a full vacuum source. then you are done. no readjustment necessary UNLESS you are getting knock.

Your absolutely correct. After our recent build, we set the base timing and ensured all in at 36* and at a steady 2700RPM. After setting the base timing there was no need to check or re-adjust.

 

[GerryLP]

Glad to help folks understand timing and vacuum advance; I'm the retired GM/Chrysler engineer who wrote it .

I thought that I recognized the article, JohnZ. I was beginning to think that someone's work was getting plagiarized.

GerryLP:cool