Discussion in 'Inboards' started by mikealston2428, Apr 7, 2015.

  1. mikealston2428
    Joined: Jul 2011
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    Location: aussie

    mikealston2428 Senior Member

    Hi All,
    Timing a chevy 350 small block.
    Get engine up to running temperature, remove vacuum hose reduce revs to 500rpm, with timing light adjust to 8 degrees after top dead Centre.
    Is this correct guys ??
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Is the vacuum hose plugged after you pull it off the advance can? Yeah, 8 BTDC is the spec for first and second gen small blocks, but a lot of things can make you want to change this. In reality, you'll likely run between 3 -4 to maybe as much as 12 - 13 degrees of timing, each engine is different loaded up.

    I usually set the timing just before a knock (spark) starts up. I load up the engine (tie the boat and put it in gear) and advance the timing a degree at a time until the thing "pre-ignites" , then back off a degree or two.

    Most advance settings are carb tune dependent, which are subject to the cam profile and any other mods you might have done, like porting, valve seat angles, head work, etc. If the engine is basically stock, somewhere between 6 and 10 is where you'll find the sweet spot.
  3. mreoe4sure
    Joined: Jul 2009
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    Location: trustafarian land

    mreoe4sure who me

    Par is correct about timing. He said before top dead center, you said after top dead center which is important. Setting it 8 after top dead center the thing would run terrible. If everything is stock ( no re-curve on distributor) 8 BTDC is a starting point and sometime you can go closer to 12 degrees BTDC if you don't get Knock. The only problem you get with Advancing the initial timing too far as it tends to cause starter problems later down the line. The starter is trying to work against the motor on startup. I replaced 100s of starters in the 1970s from Dyno tuners Removing timing in the distributor and adding it at initial timing ( as much as 16 degrees) to make cars run decent during early smog control years .Small blocks run best at between 34 to 38 degrees total timing ( initial + mechanical + vacuum). Vacuum advance is for fuel economy, it only works at high manifold vacuum. That is why the vacuum hookup it is above the throttle plate . When you give it throttle that port is opened , if accelerating hard there is low manifold vacuum and it won't overcome the spring in the vacuum advance. When the engine come up to speed the manifold vacuum rises and it can overcome the spring and advance the timing. If you accelerate slowly manifold vacuum stays high and the advance will work. When you hit the throttle hard ( not from idle)you will loose timing for a while. This stops detonation or knock which will destroy your engine. All this is now done with the computer. Steve

  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Are you talking about a car? Marine distributors don't have vacuum hoses. The load doesn't change like on a car.
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