Slight Pinging with Wide Open Throttle

I was getting some pinging when I was in 3rd or 4th gear and I decided to punch it. The extra strain or the drop in vacuum caused some slight pinging for a sec. It has been slight and only occurs with wide open throttle.

I was originally running 12 degrees advance and moved it back to 9 degrees. This helped but still very slight pinging. The car still was doing great with 9 degrees advance.

Yesterday I added 2 gallons of 110 octane to a tank of 93 octane. From my calculations I ended up with 95 octane. There was no pinging whatsoever.

Not sure where to go from here. Maybe drop the advance to 7-8 and try again. I still have my original distributer that I recurved that I have not dropped in yet. I may have to try it soon and see if it may be better.

If you ever want to mix your fuel to achieve higher octane below is the calculation.

Mixed Octane = ((fuel1Octane x fuel1Gallons) + (fuel2Octane x fuel2Gallons) ) / (total number of gallons)

6 thoughts on “Slight Pinging with Wide Open Throttle

  1. Harold,

    My old Tune-up guides state for 68 Firebird /w400HO the following specs:

    Dwell Contact Gap SP Gap TIMING StdTrnIdel AutoIdel
    30 .016 .035 9D@650rpm 850 650

    I would not go over 9 unless the engine does not ping. Ping is “pre-ignition” firing. i.e. Fuel/air mixture is ignited before piston is at TDC. So you can see the obvious engine damage that could occur. Valve reliefs in the piston top are nice to have. I would check you vac lines and advance pod etc. Make sure you have no leaks.

    • I took the advice of Jim Lahart at http://centralvirginiamachine.com/default.aspx under his services you can see his recommendation for a Pontiac 400 street engine. My builder worked with him on it and replicated his build.

      Here is some detail on my build. http://www.firebird400ho.com/engine-shop/

      We lowed the compression by dishing the pistons and used a Comp Cam XE262H. We had hoped to lower the compression to 9.2 we may have missed it a little because it still likes 94-95 octane. It can run fine on 93 if I wide open throttle slowly but if I push the throttle down all at once there s a little pinging for a couple seconds. If I run 95 octane, no pinging.

      The dyno we did put the engine 365Hp @ 5400 rpm and torq 445 @3400

      It has been real good pehavior on street. Plenty of vacuum. No over heating problems.

      • The guy rebuilding my engine said the actual compression ratio was much lower than the 10.75 advertised. He had one on the engine running stand that had #15 heads that had been worked and a 041 cam. He ran it for me and it ran great with good vacuum on 87 octane. He has been building just Pontiac 400’s for years. Mine will have all the same parts except 16 heads and the factory 068 cam. I opted to keep the points in the 1111449 distributor. I looked up the pertronics and am having second thoughts about staying with points. My engine will be run and tuned with my carburetor and distributor. Where did you get your exhaust from? I have same long branch headers and would like to stay above convertible brace.

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