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Setting Timing for best mileage & power

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Hossbaby50, Dec 31, 2002.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    I am driving to Colorado next week. Sofar I set my timing to 4* BTDC like the emission sticker in the engine bay says. I want to know any tips on tuning for mileage and tuning for power. I am running a stockish 350 with MSD, dual exhaust, K&N, and new plugs if that helps any.

    Should I try an advance or retard the timing for better mileage?

    Should I try an advance or retard the timing for better power?

    Thanks
    Harley
     
  2. Hossbaby50

    Hossbaby50 3/4 ton status

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    I am assuming that the stock 4* BTDC is probably about the best for mileage as that is what the factory was after along with least emissions. And also that more degrees advanced would be better for power. Is this right?

    What is your timing at and is there any reason you have it set there if it is not stock. Thanks

    Harley
     
  3. Highlander

    Highlander 1/2 ton status

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    I set mine at 10 deg. If I remember right you will want to advance the timing for the altitude.

    Eric
     
  4. 84_Chevy_K10

    84_Chevy_K10 Banned

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    In order to do something that matters you have to re-curve your distributor with a kit. You have to mess with more than initial timing to do something.

    I'd bump it up to 8-10* myself if you do nothing else.

    I personally run 10 initial 24 mechanical for a total of 34 on my 305 in the big truck. I run full vacuum at idle for better idle quality and hopefully better cruising fuel mileage. Vacuum advance is limited to 10* total.
     
  5. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    The more the merrier, like 45+ degrees total. HEIs, when working properly, give 20 degrees of centrifigual advance. Most SBCs make the best power around 34-38 degrees total mechanical advance. So that means your initial should be around 14-18 because your centrigual will add 20. Go for 14 just to be safe. Fastburn style heads actually work best at 14 and open chamber style heads nead a little more. Now that you've got a fair amount of mechanical advance for performance, you need a little more for mileage, enter vacuum advance. Vac advance can be anywhere between 8-16. Generally, more is better for fuel economy. You can buy adjustable units, buy different rated cans, or make your own limiter. Keep adding more until performance falls off or spark knock occurs. Hook it up to a ported source. I have no clue how ported and full vacuum got to be though of as polar opposites, they're not. Ported is located just above throttle blade to not allow vac advance when at low throttle. You wouldn't want 14 degrees initial and 16 degrees vac advance at idle. That would be 30 degrees /forums/images/graemlins/eek.gif. Anyways, after the throttle is open, its just the same as full manifold vacuum. Now if it were sourced right by the booster, than yes, it would pull more at WOT, but it doesn't. Silly people. /forums/images/graemlins/wink.gif Oh, you want all your centrifgual advance in at just under about 3,000 grand. Your stock weights and springs should do this if they are in good condition. Again, contrary to popular belief, most stock centrifigual setups are good and don't have to be up to redline to get it in. After using two aftermarket kits, I'm back to stock GM stuff, /forums/images/graemlins/rotfl.gif
     
  6. bigblock454

    bigblock454 Clack Clack Clack Premium Member

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    Blazer Boy pretty much nailed it. You want to run as much timing advance as possible without detonation. That is one of the beauties of F.I. At cruise the new Vortec FI computers will advance the timing until the engine starts to knock, then back off a degree or 2. It does this constantly when cruising at part throttle. One of the reasons GM set it at 4 degress is for emissions, they traded some milage for the EPA.
     

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