1967 327/350HP Tuning Issues - NCRS Discussion Boards

1967 327/350HP Tuning Issues

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  • Salvatore I.
    Expired
    • April 1, 2004
    • 114

    1967 327/350HP Tuning Issues

    Hi, Everyone:
    Sorry for this long post, but I am enjoying an interesting learning experience. I am not an expert, so I thought I would ask the experts for some advice.

    Engine had been rebuilt before I bought the car. While it is the original engine, there is a mild cam in the motor. "Normal" engine vacuum has been about 15 inches and there is a slight flutter, I assume from the overlap of the valves. The motor also has the Breakerless SE module in the distributor....

    I noticed that the timing was set at what appeared to be about 14 or 16 degrees advanced. I had no issues, no pre-ignition or run on and no noises that I could hear from the motor at mild or harder acceleration. But, I reset the timing to spec at 10 degrees BTDC and didn't think about it any further. I have fairly good drivability; a bit of a hard start when cold but after 2 tries, runs to warm up fine. Good, not great, acceleration but then again I do NOT have a heavy foot. No smoke. No oil burning. In fact, I recently sent an oil sample out to Blackstone Labs for an engine oil analysis and everything was great; all below usual readings...Don't use the car that much, maybe 1,500 miles per year.
    I replaced the PCV as it was "popping" but the popping has not disappeared with the new one. I put a vacuum gauge on the motor and to my surprise, I am getting a low 10-12 reading and it is moving a few inches to either side of the 11 mark... When I accelerate, the vacuum gauge smooths out and does what a "normal" engine would do, drops on acceleration to about 4 or 5 and then soars to 25 or so and settles back with a shake at about 11-12...I have snugged the intake manifold bolts and also the carb gasket bolts thinking a vacuum leak. No change. No leaks I can see with the carb cleaner method, etc...However, when I pull the brake booster line off the intake manifold to put the gauge on the motor, I can hear a sputtering in the vacuum and that is what is being conveyed to the gauge.

    Needless to say I have done a lot of studying of this subject in the past 2 weeks. I read worn valve guides would give such a reading. A possible blown head gasket, etc and so on, may also give such a reading, but my gut tells me this is not it.

    Short of doing other engine tests, is it possible that the timing is retarded for this motor at 10 degrees BTDC? Is it possible that the 14-16 degrees was set this way for this motor/cam set up?

    Before I reset the timing for maximum vacuum and ignore the timing light, what is the Forum's thoughts about my advancing the timing back to the 14-16 area? What are the risks with doing and running the motor at such an advanced point?

    BTW, the dwell meter is telling me 40 degrees rather than the spec 30....I assume the Breakerless module is compensating for the retarded ignition...is that a reasonable thought?
  • William C.
    NCRS Past President
    • May 31, 1975
    • 6037

    #2
    Re: 1967 327/350HP Tuning Issues

    Well for starters, the breakerless unit will not know what the timing is, so it will not adjust which takes one item out of the question. I could not find in your question what the idle speed is when checking the vacuum nor any information on the "slightly diffrerent" camshaft installed. The stock 327/350 cam is right about at the limits of the "idle Quality" spectrum and at a low idle speed, any bigger camshaft might well drop the vacuum to a low level. Without knowing more about the rpm you are seeing the low vacuum reading at, as compared to the rpm at the previous idle specs. it's pretty tough to diagnose anything.
    Bill Clupper #618

    Comment

    • Salvatore I.
      Expired
      • April 1, 2004
      • 114

      #3
      Re: 1967 327/350HP Tuning Issues

      Hi, Bill

      Idle is at 750-800RPM

      Comment

      • William C.
        NCRS Past President
        • May 31, 1975
        • 6037

        #4
        Re: 1967 327/350HP Tuning Issues

        How much do you know about the specs on the camshaft? Is the vacuum advance in play during your vacuum check? Full time vacuum or ported vacuum? How much centrifugal advance is in the distributor, and how is it added vs rpm? My initial thought is that the initial timing was advanced to compensate for the loss of low speed performance with the new cam. In that case, dropping the initial timing would cause a corresponding lower vacuum reading as the throttle would require more opening to maintain the idle speed (I'm assuming the idle speed was adjusted after the timing was reset)
        Bill Clupper #618

        Comment

        • Salvatore I.
          Expired
          • April 1, 2004
          • 114

          #5
          Re: 1967 327/350HP Tuning Issues

          Bill
          I am no expert...I have nothing on the cam and what it is....I am using my ear to hear that is not a very radical cam; a milder tone on the motor....I am going to increase the timing and see if it works....hopefully, I won't blow up the motor!

          Comment

          • Salvatore I.
            Expired
            • April 1, 2004
            • 114

            #6
            Re: 1967 327/350HP Tuning Issues

            The vaccum line is disconnected and plugged when I am doing these tests. The engine idle is now at 750 or so with the timing at 10 degrees advanced. When it was brought down to 10, I do recall resetting the idle to be much lower...Vacuum is low as described.

            Unfortunately, I don't know what the spec is on the cam but, as noted, I do believe it is a milder one...nothing very radical at all.

            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15667

              #7
              Re: 1967 327/350HP Tuning Issues

              Vacuum leak, aftermarket cam with more than OE overlap...

              What's the number of the installed VAC?

              Check idle timing with the VAC signal line installed. I should be the sum of initial plus maximum vacuum advance.

              Duke

              Comment

              • Salvatore I.
                Expired
                • April 1, 2004
                • 114

                #8
                Re: 1967 327/350HP Tuning Issues

                Hi, Duke

                The vac advance is the one from Napa that you have advised on previous posts...

                I set the timing by max vacuum and got about 14-15...when I took it for a run at 60MPH, I could hear pinging/detonation ...slowed down and reset the timing with a timing light to just about 12 degrees BTDC--about 2 degrees more advanced than spec...and the car is running ok .....the vacuum gauge has steadied a bit but it is still running at about 11 inches.

                No smoke. No pinging. Good power/acceleration...just really low vacuum....Guess I will let it be as this has now reached beyond my abilities.

                Comment

                • Duke W.
                  Beyond Control Poster
                  • January 1, 1993
                  • 15667

                  #9
                  Re: 1967 327/350HP Tuning Issues

                  That doesn't answer the question. What is the number? I can't help unless I have facts and accurate test data.

                  Is the VAC connected to a full time vacuum source?

                  Have you checked the idle timing with the VAC connected?

                  What is it at what initial timing?

                  What about the centrifugal advance curve. Have you checked it? Does it match OE or is it modified?



                  Duke

                  Comment

                  • Salvatore I.
                    Expired
                    • April 1, 2004
                    • 114

                    #10
                    Re: 1967 327/350HP Tuning Issues

                    What is the number? I can't help unless I have facts and accurate test data. I will have to take a look...don't know off hand...

                    Is the VAC connected to a full time vacuum source? Yes, I think so, I connected my vacuum gauge to the intake manifold connection behind the carb where the brake booster connects to the manifold; the line to the cannister runs, as per spec, to the front of the carb.

                    Have you checked the idle timing with the VAC connected? Yes, when the car is idling at about 750 rpm, I get a vacuum reading of about 10-11...this translates to a timing of about 10 degrees...Is this what you are asking?

                    What is it at what initial timing?

                    What about the centrifugal advance curve. Have you checked it? Does it match OE or is it modified? Duke, don't have a clue about what you are asking here...how would I measure it? Remember please I am no expert....please spell out what this is....Thanks.

                    Comment

                    • Duke W.
                      Beyond Control Poster
                      • January 1, 1993
                      • 15667

                      #11
                      Re: 1967 327/350HP Tuning Issues

                      Have you checked the idle timing with the VAC connected? Yes, when the car is idling at about 750 rpm, I get a vacuum reading of about 10-11...this translates to a timing of about 10 degrees...Is this what you are asking?

                      You set the initial timing with the VAC disconnected with the engine at below normal idle speed - as low as you can get it.

                      Then connect the VAC set the idle speed and mixture and look at the timing again. It should be the sum of initial and full vacuum advance, which should be known once the VAC ID number is revealed.

                      You check centrifugal with a dial back timing light and the VAC disconnected. Find the start point, measure in 500 to 1000 RPM increments from there until you find the maximum.

                      Specs are in your CSM.

                      Duke


                      Comment

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