Took our GMC to a DynoShop that specializes in RV's and other large engine
trucks. [DyoShop, Santee, CA] 'Bin in business over 20 years so GMC old
hat for them. Had them tune it for 87 octane in tank. I also had installed
the Platinum and Rhenium vapor injection to replace "lead" so it would not
{and it does not] ping on 87 octane. The tuning reset the distributor 10
degrees at 700 rpm and from 8 [was] to 22 degrees centrifugal advance at
4000 rpm[on bench]and 16 degrees vacuum advance. The carburetor power
circuit was changed to come in a 5 inch of vacuum rather than 11 inches
which was where it was at[much to rich and probably why we only averaged
9.1 mpg across country]. Autolite 565 gap set at .060" for the new Jacobs
ignition. Vacuum idle is 20 inches. Coke on old plugs and tailpipe from
10,000 mile old carburetor rebuild and cold starting problems were the
reason for the dyno tune.
Our coach is only 10,000 lbs fully loaded and has the 3.42 drive so it now
will cruise up the local 6% grades in cruise control at the 65 mph speed
limit. I stepped on the accelerator and ran it up past 70 and it was still
gaining when I backed off because of the traffic. We will report back on
the milage after our summer trip of ~15K.
Chuck Botts, San Diego, Ca.
trucks. [DyoShop, Santee, CA] 'Bin in business over 20 years so GMC old
hat for them. Had them tune it for 87 octane in tank. I also had installed
the Platinum and Rhenium vapor injection to replace "lead" so it would not
{and it does not] ping on 87 octane. The tuning reset the distributor 10
degrees at 700 rpm and from 8 [was] to 22 degrees centrifugal advance at
4000 rpm[on bench]and 16 degrees vacuum advance. The carburetor power
circuit was changed to come in a 5 inch of vacuum rather than 11 inches
which was where it was at[much to rich and probably why we only averaged
9.1 mpg across country]. Autolite 565 gap set at .060" for the new Jacobs
ignition. Vacuum idle is 20 inches. Coke on old plugs and tailpipe from
10,000 mile old carburetor rebuild and cold starting problems were the
reason for the dyno tune.
Our coach is only 10,000 lbs fully loaded and has the 3.42 drive so it now
will cruise up the local 6% grades in cruise control at the 65 mph speed
limit. I stepped on the accelerator and ran it up past 70 and it was still
gaining when I backed off because of the traffic. We will report back on
the milage after our summer trip of ~15K.
Chuck Botts, San Diego, Ca.
