454 Vacuum Advance question

[ClydesdaleKevin]

Just making sure I have this right before attacking the vacuum line routing...the very confusing and overly complicated vacuum line routing...on the the RV this week.

On an 89 Chevy 454 with a carburetor and HEI ignition, the vacuum line coming to the distributor should be timed vacuum, correct?  In other words, it shouldn't be hooked up to a fulltime vacuum port, but to a port that creates vacuum at a higher RPM, correct?

I'll be simplifying my vacuum routing this week and eliminating a few, and modifying my air box for better airflow and a tighter seal with the spacer this week, so I want to make sure I have that one little detail down.

Thanks!

Kev

[Mytdawg]

I beat my head against the wall on this for the Corvette for some time.  The short answer is yes.  Most of the time.  I think.

My understanding is that if you run full instead of timed you'll have full vacuum advance at idle.  It's great if the motor is tuned for that because it will give you acceleration off the line.  Likely at the cost of efficiency but not necessarily.  However it could cause problems in smog motors with detonation at low engine speeds.  You get into a grey area with performance engines because if you are able to run enough advance and octane then full vacuum may be preferable.  Supposedly the timed port was created so they could lean out the idle mix and keep the smog motors running.  They won't idle without it.  I'm sure it's all kinds of fun if you have to pass an emission inspection.

The Corvette runs different with every change in temp and humidity.  I believe I ended up advancing it a little manually and leaving it on timed.  But if I don't run premium I have to back it down a little.  I went through 3 carbs trying to find a combination that worked.  Some days it still won't idle right.

Your results may vary.  If the timed port seems to be working for you then I'd go with it.

[ClydesdaleKevin]

No smog tests where we are registered in Florida.  Just want it to run as efficiently as possible, while still having the power needed to climb the hills. 

The Edelbrock 1411 is working way better than the Rochester Quadrajet did, but only getting about 6 mpg right now, so I'm going to redo the vacuum lines, check the timing, and modify or replace my air cleaner for better air flow. 

I'll be playing with it this week, but just want to make sure I hook the distributor advance up to the correct port on the Edelbrock.

The vacuum diagram on the stock air cleaner lid is confusing, showing the vacuum line from the distributor going to a delay valve, then to another valve, then to a port on the RQJ...which I'll have to physically look at tomorrow to see if its above the valves (timed), or below (full time). 

Was just hoping for an easy answer...lol!

Kev

[Mytdawg]

If it's running good, you are already winning...   

[DaveVA78Chieftain]

Should be connected to ported (timed) vacuum.  Has to do with emission control settings at idle.  This is most likely via other vacuum controls though.

Dave