Project80

With a 1980 HEI distributor, does the vacuum line going to the carb get connected to a ported vacuum source or is it manifold vacuum? In other words, is the connection above or below the throttle plates? My routing diagram only shows the hose going to the carb.

pws69

Distributor vacuum is ALWAYS "below the throttle plates" whether it is manifold or ported - which are exactly the same EXCEPT at idle. See which one the car runs best with - usually manifold is preferred, but ymmv.

MakoShark72

Recent discussion on the subject...

http://forums.corvetteforum.com/show...=timing+vacuum

CA-Legal-Vette

That was a very good write up. Missed it first time around.

There is also a good paper that Lars has written with another author his name escapes me) on choosing the right vacuum advance. Drop him a line for a copy.

BarryK

this is it:
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf

It's on my tech articles page under the Timing & Vacuum Advance header

Project80

Thanks for the link to the write up.
But, I was hoping that somebody might know how the vacuum connection originally came in 1980.

lars

It went to a thermostatic temperature switch which had the ability to switch between ported, manifold and no vacuum depending on engine temperature.
Lars

thegazman

Here's a picture of my 1979 with a Q-Jet carb. On my car the ported vacuum is the small line on the left front of the car. Your's will probably be the same.

7T1vette

Being "above or below the throttle plates" has little to do with where the vacuum port is located on the carburetor. Internal cast & drilled passages can allow 'manifold' vacuum to be up on the side of the carb body. The easy way to figure out if a port is linked to manifold or not is to remove the hose and see if a scrap of paper will remain held by the vacuum or not [when car is idling]. If it won't stay on the end of the port, it's "ported".

lars

That's not correct. If that's a '79 carb, the port on the forward driver's side of the carb is manifold vacuum. The ported vacuum port after 1975 is located on the forward passenger side corner of the carb throttle plate, pointing out at a 45-degree angle, and it was used to operate the EGR.
Lars