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Thread: MSD 6530 boost and run retard curve advice for Weiand 142 Chevy 350

  1. #1
    Join Date
    Aug 2018
    Posts
    4

    Default MSD 6530 boost and run retard curve advice for Weiand 142 Chevy 350

    Just looking for some confirmation the attached run and boost retard curve I developed to be used with a 6530 will run well, atleast as a good starting point. Name of the game is reliability while still making good power, not looking for max power. I'd be locking the distributor out at 40 degrees.

    Stock low comp (8.0:1 compression) 350 four bolt main revving to 5,000, stock cam
    Weiand 142 running 6-8 psi
    Holley Super Sniper EFI
    1 5/8" long tubes out to a 2.5 inch exhaust
    4 speed Muncie, 3:08 rear gear
    Everythings in a 2wd long bed 1972 C10 so about 3600 pounds, never had it weighed though

    timing curve.jpg

    The way this is set up (If I'm understanding everything correctly) I should have a 25 degree start retard so cranking at an easy 15 degrees. Initial timing is 18 degrees with 30 degrees of total timing coming in by 2500 rpm. "Vacuum advance" is adding 10 degree's of advance at 7-8 inches of vacuum and greater. Once boost builds, 1 degree is pulled per pound of PSI up to 3 PSI, and then it increases to roughly 1.2 degrees per pound for some added safety. I also added 1 degree of retard above 4000 rpm as a bit more cushion.

    1. Is this correct?
    2. If so, is this a good starting point?
    3. Does this seem too conservative?
    4. Anything that should be changed?

    At some point I'll most likely wire up the Sniper to control timing but I want to make sure I'm understanding how this works as I'll be have to configure the Holley in a similar fashion. For my purposes, this 6530 is easier to change on the fly and monitor timing for the initial start up and tuning. Thanks for any help!

  2. #2
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    955

    Default

    The TOTAL sum of of all retards can only be 25 degrees.

    You have 15 retard in your run curve, so the engine will be cranking, and idling at 25 BTDC.

    You have 40 total, the spark will then be jumping to the the next cylinder, and hence the engine will stop running.

    So it would be best to have 12 or so in the run curve and 12 in the boost curve.

    You might be better with a mechanical curve, not locked out, trim that with a small amount in the run curve, and then have your boost retard curve.

    Gary
    Last edited by Gaz64; 09-02-2018 at 08:36 PM.
    Regards

    Gary

  3. #3
    Join Date
    Aug 2018
    Posts
    4

    Default

    From what I see, I have 15 degrees of retard during cranking from 0-400 rpm from the run retard and another 10 coming out when the MAP sensor see's around 14.7 psi (atmospheric pressure) so a total of 25 degrees being taken out during cranking. Once the motor idles and see's moderate vacuum, the boost/vacuum retard is taken out and only 15 degrees is being pulled, so 25 degrees at idle.
    Are we looking at the same graph?

    I also will have rotor phasing corrected with an adjustable rotor to compensate for the extreme advance, I see that as pretty much unavoidable when running these type of units.

    I also don't understand how its possible to run a mechanical and run curve. The distributor has to be locked out in order to use the 6530. The run retard simulates and functions like the mechanical advance except with more ability to custom tailor the curve.

    Can anyone chime in to confirm this?

  4. #4
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    955

    Default

    Ah, yes I see your combo while cranking, and yes that should be correct of 25 retard.

    I would convert to a large cap combo.

    Sorry for the confusion about mechanical advance, that only works with another make of ignition.

    Gary
    Regards

    Gary

  5. #5
    Join Date
    Aug 2018
    Posts
    4

    Default

    No worries, appreciate the reply.
    Why go to the large cap combo? To spread the terminals out more?
    I did consider it previously but the clearance between the blower and distributor is minimal so I didn't want to chance it.

  6. #6
    Join Date
    Aug 2018
    Posts
    4

    Default

    can anyone from MSD chime in on this timing curve?

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