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  1. #1
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    Default 308 Carb/Quadrajet tuning

    I have a 308, m21 4 speed, 3.00 9 inch diff in a WB ute.

    204/214 @ 0.050 camshaft, 9.00:1 CR, Edelbrock performer dual plane intake manifold, ICE Adjustable HEI, Ceramic extractors and a good flowing exhaust.

    The car is a daily driver and sees 100 highway kms per day.

    Regardless if whether I use my Quadrajet or 500cfm Edelbrock AVS2 I get the following stats (I have tuned the jets/rods as best I can):

    Vacuum:

    At idle: 17"
    On highway(100/110) : 15-17"
    Cruising (any gear but 4th) : 20-21"

    AFR (using O2 sensor in LH exhaust bank)
    At idle: 14
    On highway (100/110) : 13-14 range
    Cruising (any gear but 4th) 14.5-15
    Power circuit : 13
    WOT : 12 (a bit rich, but I barely go over half throttle)

    Timing:

    Initial: 14 (best vacuum)
    Total: 30 @ 2800rpm
    Vac advance : 10 degrees @15" vacuum

    I want to get the AFR up to around 14.5-15 on the highway for a bit better economy etc however only in 4th gear does it run a poofteenth rich.

    Any ideas why?

  2. #2
    Do you ever leave? EH179's Avatar
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    If you run 98 octane fuel, try raising the total timing to 32 and see what the gauge says.

    The extra timing may help burn the fuel on the H'way, increase vacuum and economy.

    Might even want 34 total, suck it and see.

  3. #3
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    Agree with EH about more timing.

    If I am reading the numbers correctly, you have a total of 40* at cruise. That is really low for 9.0:1 CR. I would add at least another 5 -10* of vac adv. That in itself should lean the mixture slightly & improve economy.

    45-55* cruise timing is the 'normal' range, but I have occasionally used over 60* with big cams/low CRs.

  4. #4
    been here .......too long Smitty2's Avatar
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    Quote Originally Posted by EH179 View Post
    If you run 98 octane fuel, try raising the total timing to 32 and see what the gauge says.

    The extra timing may help burn the fuel on the H'way, increase vacuum and economy.

    Might even want 34 total, suck it and see.
    .. agree with that
    whack your initial up from 14 to 18 and see what the result is

    also curious... what primary rods and jets are you using in the Quaddie?
    and what secondary rods? DP? CE? or...?
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  5. #5
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    Quote Originally Posted by Smitty2 View Post
    .. agree with that
    whack your initial up from 14 to 18 and see what the result is

    also curious... what primary rods and jets are you using in the Quaddie?
    and what secondary rods? DP? CE? or...?
    I will try changing my total to 34 using the highest of the 16 presets ICE Igniton has first and see how I go.

    The Quaddie was factory WB 308 settings with the 71 Jet however it had a lean surge and showed up to 17 on the AFR Gauge, I changed to a 73 Jet with whatever factory rods it had and it brought it down to a more comfortable level.

    Same goes for secondary rods, whatever WB 308 had for factory (603 model I believe).


    I do have a Bosch HEI distributor and HEC style coil in the shed, what kind of advance would these normally give (Ie how much vac advance do they give, and what kind of mech advance in numbers and what rpm are they all in) - of course assuming it hasn't been tampered with.

  6. #6
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    Quote Originally Posted by GtoGeoff View Post
    Agree with EH about more timing.

    If I am reading the numbers correctly, you have a total of 40* at cruise. That is really low for 9.0:1 CR. I would add at least another 5 -10* of vac adv. That in itself should lean the mixture slightly & improve economy.

    45-55* cruise timing is the 'normal' range, but I have occasionally used over 60* with big cams/low CRs.
    Although possibly a silly question, how would I go about getting a much higher cruising timing without effecting other things?

  7. #7
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    Not a silly question. VA, whether ported or manifold sourced, is a load sensitive device, based on engine load & vacuum. That is the beauty of it. When you go to full throttle, vac drops to zero or very close; so the VA drops away to zero & all that extra cruise timing is gone.

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