News

MSD question

Discussion in 'Technical Q&A' started by snj5, Nov 19, 2003.

  1. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Is an MSD box able to take it's 'direct battery wire' (as opposed to
    the switched input) connection off the starter or will the voltage
    fluctuation fry it?

    Will it add substantially an optically triggered distributor system with a high performance coil?

    Thanks
    Russ
     
  2. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,427
    The twilight zone
    Full Name:
    The Butcher
    Here's my guess. The voltage drop won't damage it, but it won't have the output it should while the engine is cranking. I mounted my new electronics where the old stuff came out and just used the OEM power wires. Also, there is a connector over the rear driver side wheel (you need to pull the wheel well) where you could tap the power that used to go to your FI if that helps.

    If you are running stock compression, I seriously doubt you will see any improvement adding the MSD box. The spark just needs to be able to jump the gap at the plug and you haven't done anything to make that a problem. High cylinder pressure, like from a high CR or a turbo/blower often means more voltage is required.
     
  3. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,558
    Chicago
    Full Name:
    Philip
    Russ
    Don't have a perspective on the voltage question except to say I run my Electromotive coils from a relay off the starter.

    Second, one advantage of the MSD is going to be a stronger spark. I remember an Alfa I owned in Australia 15 years ago. Run the AC in traffic (more load) and it used to try to oil up the plugs. Needed to "blip" the throttle to keep it running. Issue was voltage put out by the coils.

    People report excellent results from the MSD.
     
  4. bill365

    bill365 F1 Rookie

    Nov 3, 2003
    3,319
    Chicago area
    Full Name:
    Bill
    Hi Russ and mk e,
    Actually you shouldn't see any different voltage drop at the main feed to the starter than at any other point in the harness.

    As for the "substantial" difference, that is a matter of discernment, some say there is quite a noticeable difference some say no. The main difference between the MSD and a standard "simple" optical trigger and coil setup is that the MSD boxes, 6 and up, are Multiple Spark Discharge. Meaning that in the low RPM ranges there are a number of sparks for a duration of (as I remember) 10 to 20 degrees crank rotation, instead of one spark.

    The AL models ie: 6AL, incorporate an adjustable rev limiter, which when activated by hitting the preset limit, it shorts out one cylinder at a time (different cylinder every rotation).

    There are differing points of view, as for whether spark duration or spark amperage is better for getting the most efficient combustion job done.

    Judging by the widespread use in race cars, I guess they like MSD's a lot

    Regards,
    Bill
     
  5. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    Bill is right in that the voltage drop at the starter won't be any worse. Why? Because the battery goes *first* to the starter, then to the fuse panel/ign switch. The starter is the closest point to the battery. If you use a power source routed thru the ign switch, it's already been to the starter and back. Look at your wiring diagram to see what I mean. The starter is the main junction for the battery, alternator, and fuse box.
     
  6. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,849
    4re gt4 - Perhaps a little more discussion is called for. If you look at your schematic, you will see one large gauge wire going directly to the starter, but there is a 2nd wire coming off of the battery terminal to a shunt resistor ( across the ampere meter ) to the ignition switch. It is this 2nd conductor that provides all of the current for the various loads of the car. Connecting the MSD to the starter terminal, in theory, could result in voltage drop during cranking that might impact the MSD unit, however, in practice this is unlikely. The voltage drop results from the combined resistance of the battery connector, conductor, and terminal connector at the starter. When drawing 50+ amps during starting, the voltage drop could be 1 or 2 volts. Unlikely that this will impact the MSD, but in theory, possible.

    If the connection is that much easier, then I would try it to see if there are any issues. If it is easy, then I would go to a site that is on the 2nd conductor coming off of the battery.

    Mk-e - As far as MSD leading to "better performance", in a well-tuned engine, irrespective of compression ratio, there should be little difference. A spark is a spark, and the fuel/air mixture is not animate. It is rather unemotional about the "quality" of the spark. However, if the state of engine tune is such that the plugs tend to become "wet" with rich fuel mixture or oil, then the higher voltage of discharge of the MSD can improve drivability by providing higher voltage at the spark gap. The voltage necessary to "spark" will be higher if the plug is wet. Thus, MSDs will work where lesser systems will foul.

    Jim S.
     
  7. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,325
    Texas
    Full Name:
    Steve Magnusson
    I believe you need to be model specific to determine the impact of the "+" power routing on your question -- i.e, 308s are per 4re gt4's description while the later cars are per Jim S.'s description (so I'd guess an '88 Mondial would be per Jim S.'s description if you're talking about your Profile car Russ).
     
  8. bill365

    bill365 F1 Rookie

    Nov 3, 2003
    3,319
    Chicago area
    Full Name:
    Bill
    Jim,
    I believe what you would be seeing in the shunt resistor is a negligible voltage drop to all of the switched accessories other than the starter. Shunts are generally of very low resistance when used in this manner, probably well under .1 ohm, for the ammeter (which is usually a sensitive zero centered voltmeter) to react to a very small variance in voltage read across the shunt.

    As I understand the original question, Russ wants to hook up the MSD box to the unswitched battery lead on the starter (direct from the battery) and maybe I read a little more into this but then provide power switching to the MSD unit, as in high watt accessory lamps or horns, with a relay which may be energized by any switched power source. The degree of benefit in this arrangement I wouldn't care to guess at this time, but this is the way I took the question.

    The main MSD features are not the intensity of the spark, it is the multiple spark discharge, hence the chosen name MSD, and the optional selectable advance and rev limiter. There are other features available but most others are more related to drag racing.
     
  9. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    James: Perhaps it is model specific. On my car, the One And Only lead from the battery goes directly to the starter. Therefore, the voltage at the starter would have the least 'drop' of anything else on the entire car. There is no other 2nd 'shunt wire'. In fact, most (all?) of the 308 series don't have an ammeter, so such a 'shunt wire' isn't needed.
     
  10. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,849
    Perhaps it is model specific, but I have checked my Dino, Testarossa, and Boxer, and all have 2 leads off the battery: One direct to the starter (a very large conductor) and a second to either the ignition switch or shunt bypass for the ampere meter. This includes the Testarossa, which like the 308, does not have an ampere meter (the lead goes to the main bus at the relay board).

    I agree that connecting the MSD to the starter terminal introduces the potential for voltage drop during startup (when large current is being pulled through the starter conductor), but I suspect that most automotive electronics are designed to work with voltages ranging from 10 to 16 volts.

    What would happen with your MSD if you tried to start the car with a relatively weak battery, or when stalled at a traffic light, in the evening, with the lights on, with the air conditioner going, in the rain requiring windshield wipers, with the radio on, and the blinker? The voltage on the main bus is likely in the 10-volt range, and the car will start with the MSD.

    Thus, while not a prudent approach, the MSD positive lead on the starter terminal will likely work.

    Why would high compression require more voltage to induce a spark? I will have to review my CRC (Chemical Rubber Company Handbook), but the dielectric properties of a gas is likely a function of the density of the gas (read pressure), and if anything, should reduce the voltage requirements compared to a vacuum.

    You get what you pay for, and in this case, it is my worthless opinion. In case you have not noticed, it is the electrical engineer in me that tries to dispel folklore, sometimes by introducing more folklore.

    Jim S.
     
  11. Throttleman

    Throttleman Formula Junior

    Sep 26, 2003
    339
    Pasadena,CA
    Full Name:
    Jay Ablett
    I agree with earlier posts on this subject. I have used the mentiioned MSD 6AL on two high compression 10:1 and 11:1 ratio engines using far greater fuel intake than stock. In both cases when initially run on the stock distributor and coil setup, the engines were very hard to start and difficult to set proper jetting and idle speeds. With the introduction of the MSD 6AL and a Mallory 60K volt coil, the engines started up on the first crank as if they could finally breathe. In these extreme examples it was quite obvious to see that the spark was inadequate, very weak and could not burn all the fuel that was being introduced into the combustion chambers and thus fouling the plugs making the setup of the engine very difficult.

    On a stock engine with low compression and stock fuel system, I doubt the change would be dramatic other than probably much easier starts and a tiny improvement in gas mileage. These gains could likely be achieved by just swapping the stock coil with a higher voltage unit without spending the extra money on the MSD control module.

    Just my 2 cents,

    -Jay.
     
  12. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,427
    The twilight zone
    Full Name:
    The Butcher
    I think the voltage needed for a spark to jump a gap is lowest in a vaccum, but I can promise you the voltage required is higher when the cylinder pressure goes up or the mixture gets richer.

    As far as the multiple discharge, I have never seen a dyno test were it helped when compared to a similar voltage single spark system. MSD makes very good stuff and I run and MSD DIS-4 in my car. The point about helping if the plugs are getting wet makes sense, but really means that the mixture needs attention, not the spark.

    And just a heads up, if you use an MDS box, make sure the tach is not driving of the coil or you'll fry it.
     
  13. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,849
    Mk e - I am in full agreement. My Boxer has an MSD, and this seems to be the choice of many experienced Ferrari specialists who I speak with. I believe that cold starting, low RPM cruising, and immunity from fouling in older, out-of-tune engines all speak to MSD's virtues.

    Performance improvement could in theory be seen if a larger spark gap were introduced, thereby providing greater "surface area" for ignition of the flame-front. The MSD, with greater firing potential (voltage) would allow for this larger gap. However, I do not believe this aspect of ignition is exploited.

    I am not a student of MSD technology, but if I interpret Bill365's comments correctly, multiple spark is the prime feature. This makes great sense, as the turbulence in the cylinder (swirling gas) introduces new, un-burnt fuel to a 2nd or 3rd spark before this gas might have been ignited through propagation.

    Jim S.
     
  14. bill365

    bill365 F1 Rookie

    Nov 3, 2003
    3,319
    Chicago area
    Full Name:
    Bill
    "I can promise you the voltage required is higher when the cylinder pressure goes up or the mixture gets richer. "

    True, the mixture is just that, a mixture of gasses and a "atomized" liquid and does require a higher voltage to jump the gap when at a higher pressure.

    "The point about helping if the plugs are getting wet makes sense, but really means that the mixture needs attention, not the spark".

    True, except in the case of a "cammy motor", truer when carburated or non-electronic FI. The greater overlap, in a higher revving motor's cam timing, results in an inefficient burn (due to low cylinder pressure, and a richer mixture for throttle response) at low RPM (as demonstrated by Jay's hard starting problem) hence the rough or impossible low idle and the sudden surge of power when you reach the "sweet spot" in the power band. This is why most F-cars will not idle below 1K rpm.

    " if the state of engine tune is such that the plugs tend to become "wet" with rich fuel mixture or oil, then the higher voltage of discharge of the MSD can improve drivability by providing higher voltage at the spark gap. The voltage necessary to "spark" will be higher if the plug is wet."

    True, as above.

    Electronic and capacitive discharge ignitions, and high voltage coils do allow the use of wider plug gaps, which is often recommended by the manufacturers of these products, this gives a larger spark exposure to the mixture, as Steve said.

    "You get what you pay for, and in this case, it is my worthless opinion." :)->}

    Just to show I can have worthless opinions too, LOL! (;->}
     
  15. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Many thanks for the great replies!

    Using strategy of change one thing at a time, will set up the Mallory distributor and MSD coil/ballast with surge protector first and work to get the indexing, advance and tach driver sorted.

    If it will make a difference in starting, will add MSD next. Was planning on using the coil power for the switched power. Will probably try the solenoid line and test for batt power line.

    many thanks to everyone
    Russ
     
  16. Gary48

    Gary48 Guest

    Dec 30, 2003
    940
    Go ahead and attach at the terminal which is largest (Battery) wire at the starter. I did this on my 246 with an MSD 6 al. worked great. gary
     

Share This Page