>I finally have my pings all figured out. Used the medium springs on the
>weights (spring and weight rebuild kit from Mr. Gasket for HEI) and went to
>a 15 in hg. vacuum advance from GM (instead of the stock 10). Also have the
>advance set at about 12 degrees and the EKE hardly works unless I hit some
>pretty heavy hills. Road tested to K.C. and back. Works well. HTH
>
>Nate '75GB (Cloudy, cool but no rain... yet!) Omaha
Nate -- what part number Vacuum Control did you use? Since you have a
75, I assume that you have a 455 with a non-California engine. The
specs show it to be a 12 degree advance.
I took the following information from the 1975-76 GMC Maintenance
Manual and from the 1977-78 Supplement.
Distributor specs for GMC HEI Distributors
1975 & 76 455 Federal engine
Vacuum Control 1973523 (Delco-Remy)
In of Hg to start advance 8-10
In of HG for max advance 19-20
Maximum advance 12 degrees
1975 & 76 455 California engine
Vacuum Control 1973560
In of Hg to start advance 14-15
In of Hg for max advance 18-19
Maximum advance 5 degrees
1977 455 Federal
Vacuum Control 1973523
In of Hg to start advance 8-10
In of Hg for max advance 19-20
Maximum advance 24 degrees
1977-78 403 Federal
Vacuum Control 1973609
In of Hg to start advance 4-5
In of Hg for max advance 7-8
Max advance 8 degrees
1977-78 403 California
Vacuum Control 1973634
In of Hg to start advance 11
In of Hg for max advance 14
Max advance 10 degrees
I have a 1977 455 Federal (49 states - non-California) with the
1973523 Control. My idle vacuum is 14-15 degrees. I checked my
distributor with an accurate vacuum gauge and it starts to advance at
5 in Hg and has its maximum advance at 15 in Hg. The maximum advance
is 12 degrees as checked with a protractor.
Questions: 1. The 1975-76 and the 1977 Federal show the same
Vacuum Control but the max advance is shown as 12 degrees for the
75=76 and as 24 for the 1977. Is this a misprint? Does any know the
correct amounts? Should it be 12?
2. My engine is a Jasper with about 10,000 miles on it. The idle
vacuum is 14 to 15. I have been told that it should be 19-20. Note
that I am at 7200 feet elevation above sea level. If I remember
correctly I once read that for every 1000 feet in elevation the
vacuum will read about 1 in Hg lower. Since my idle vacuum is about
5 inches low and the start advance and the point where the max
advance occurs is also about 5 inches low, is that because of the
altitude and everything is working properly? The distributor does
advance 12 degrees. My engine seems to perform well.
It appears that those that have a California engine should replace
the vacuum advance if they don't own the vehicle in California. In
fact, those in California should also replace it (probably illegal
there) if they think they can still pass the emmission tests as it
should give a lot better performance.
Emery Stora
77 Kingsley
Santa Fe, NM
