Ignition Systems Question

Discussion in 'Engine Topic' started by camaro_1980, Feb 10, 2019.

  1. muscl car

    muscl car Veteran Member Lifetime Gold Member

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    Jul 8, 2001
    High Desert of Hesperia Calif
    I'm running a MSD mech adv distributor , MSD coil and MSD 7AL2 plus ignition box

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  2. K1ng0011

    K1ng0011 Veteran Member

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    Mar 22, 2014
    United States
    You really have two choices points or electronic ignition. Both work but gm moved to electronic distributors in 1974 I think and used them until the end of the era of the carburetor. Personally I like a large cap HEI vacuum advance distributor. The large cap has the coil in the cap and you dont have to worry about remotely mounting a coil its simple. Regardless of whether you run points or an electronic HEI distributor you really should learn how to properly adjust timing for maximum power/fuel economy. Most people just hook them up and go. So the next question is where to start? First what engine are you running, what cylinder heads, and how radical of a cam. With good cylinder heads your total timing will be lower than a generic head from a 70s smog era sbc. The total timing and how quickly you get there is done with a weight and spring kit. I suggest looking into this. The more radical of a cam you run the less vacuum you will have. Not producing enough vacuum can make your vacuum advance not to work but they have canisters that specifically work with less vacuum or are adjustable. Little vacuum can cause your carburetor not work right either like the metering rods wont limit fuel to the jets properly. If you make under 15 inches of vacuum you will have to start messing with stuff. Its easier to start with an engine that makes decent vacuum which most dont have crazy cams like that. In all likely hood you could probably just put in a distributor and it will work if your engine is not to crazy but if you want to get the most out of your engine you have to fine tune it. Lots of info here good luck

    Ported vs Manifold Vacuum: http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm
    Changing Weights/Springs:
    Good Timing Educational Video:

    Quick Summary:
    Tools: Timing Light,Timing Tape, Vacuum Gauge

    1.Do whatever it takes to get the engine running and warmed up.
    2.Check the vacuum the engine is making and timing at idle with the vacuum advance disconnected.
    3.Set your initial idle timing 6-20 degrees depending on cam and lock down distributor.
    4.Put timing tape on harmonic balancer
    5.Rev engine to 3000-3500RPM and verify your total timing is correct use spring/weight kit and initial timing to get it total timing correct.

    SBC Total Timing 70s Era Heads: About 36 Degrees
    HEI Vacuum Advance: Hook to Manifold Vacuum not Ported Vacuum
    Ported Vacuum: Port on carburetor w/no vacuum at idle (only for emissions)
    Check Your Total Timing Not Just Initial
    You Dont Loose Power With Vacuum Advance Distributor
    More Radical Cams Require More Timing to Idle Typically
    Total Timing @ 3000-3500RPM
    Leaner Air/Fuel Mixtures Run More Advance
    Less Vacuum=More Difficult to Tune
    More Vacuum=Easier to Tune
    Typical Vacuum Advance Adds=15 degrees of advance to timing
    Retarding Timing: Less Power, Hotter Exhaust, Less Chance of Detonation
    Advance Timing: More Power, Cooler Exhaust, More Chance of Detonation
    Engines Make Vacuum at Idle and part throttle so no affect at wide open throttle
    Mechanical Timing: The springs/weights in a distributor open outward as the rpm makes the distributor turn faster. So mechanical timing is related to RPM.
    Lots of advance during starting can kick the starter back.
    Last edited: Feb 13, 2019
  3. G72Zed

    G72Zed Veteran Member

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    Sep 8, 2015
    Lots of good information given so far.

    IMO, if you have an HEI already,(and not worn out), a good quality Cap/rotor (w/brass terminals) /wires/plugs is a great start. If the weights are rusty/cruddy/sticking, a good cleaning with some fresh springs will help.

    I have found that most of the aftermarket GM HEI curve kits are junk, I've had the best luck with the GM OEM "41" weights and the "375" center plate.

    It does take time & patience to dial in the weights & springs for the best initial/centrifugal (based on the combo & specs) and not to mention tailoring the vacuum advance opening point and amounts and centrifugal limiter if needed.

    If in need of a complete new distributor, and staying HEI, look into DUI (Davis Unified Ignition). A little pricey up here in the great white north, but very well worth it, and will handle allot of "engine upgrades" in the future. Good luck.
  4. djgriff

    djgriff Member

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    May 9, 2009
    van nuys , CA
    you did not mention what year your Camaro is > if it was originally equipped with points and you want to run an HEI be sure to not just power the HEI with the original positive that went to your coil, it is a resistor wire that limits the voltage to around 9 volts (needed to keep the points from burning up) Most of the electronic ignitions want full battery voltage and the HEI has to have full running voltage(13.5+) it sounds like you have a stock to mild set up and an HEI will work as good as any after market ignition for your needs and with the correct module, coil and brass terminal cap and rotor will work with highly modified engines even with big cam and low vacuum . all of the stuff about dialing in your advance and using good quality plug wires hold true for any ignition you choose to run. I like the HEI because it will work when properly set up to run past 7000 and if it does have a meltdown at some point you can get parts for it most any where(at least to get you home) when they do fail it is usually the module which is easy to replace and easy to get. I have had modules last for 10+ years or more and have had one that lasted 14days so I try to carry a spare just in case. I have installed many capacitive discharge type ignitions(MSD,Crane, Mallory hyfire ect) and they all run great until they don't and then you are stuck unless you carry a spare. I used to run a MSD using the stock points distributor with a set of Mallory performance points to trigger the MSD so if or when the MSD failed I could swap a couple of wires around and get home on the points.also using points to trigger a CD box the points last almost forever because they are no longer conducting high current and just a on off switch I never did have to do that cause the MSD6A I ran never gave me a problem but I have had some customers cars with newer 6a 6al ect have complete failers and cause they were either converted HEI dizzys or other magnetic /transistor electronic distributors I had to either go fix them where they were or they had to be towed I still have that 6a waiting to be used again but I like the HEI for its simple hook up and dependability and effective output(but I still carry a spare module) there is also nothing wrong running points other then they do wear and need to be adjusted and changed periodically Figure out what you are doing with your car and what you want from an ignition listen to what you are told by others that actually have first hand experience and go from there . there are more then one way to fire your cars fuel correctly and there are many more ways to mess things up even using the newest Hot set up (read expensive) if you do not have a good understanding of what is required of an ignition for your particular combo one last thought if you already have an HEI there are plenty of performance replacement parts that you can update your system with starting with Davis Unified Ignition , MSD, Pertronix , Mallory, Accel ect good luck if you have problems the people at Nasty Z28 are the greatest and with all the knowledge here I am sure you will have plenty of help to set you in the right direction
    dave@ztech likes this.
  5. biker

    biker Veteran Member

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    Dec 7, 2014
    New Liskeard Ontario Canada
    I have had 2 different DUI HEI setups (also known as Performance Distributors) and they are awesome. Quality parts with curve dialed in for your combo. My current one made a world of difference compared to a stock HEI. However, if you have access to weights, springs and an adjustable vac advance can, you can dial in a stock HEI nicely if it isn't worn out.

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