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Ignition physics for regular guys like me.

Old 11-05-2017, 11:16 PM
  #81  
sc2dave
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Hey 69427, do you still have your distributor machine? If you do, are you willing to recurve my dist for a price?
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Old 11-08-2017, 01:15 PM
  #82  
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Originally Posted by sc2dave View Post
Hey 69427, do you still have your distributor machine? If you do, are you willing to recurve my dist for a price?
I don't presently have the time or spare parts to do that (I just moved, and my garage is completely filled with boxes of unknown contents), but I'll PM you with a couple names of members here who I believe are equipped to help you out in a timely manner.
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Old 11-30-2017, 12:27 PM
  #83  
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I've been wanting to try an MSD digital HEI module. As I understand it has a microprocessor or custom controller to trigger the charging and discharge of the coil, so dwell can be dynamic thru the rpm range, I think.

The other big thing is that it has a rev limiter. This would be really helpful for my trans am 4 speed that doesn't like over rev.

Can you give a mini lecture on how this module works?
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Old 11-30-2017, 01:37 PM
  #84  
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Originally Posted by turtlevette View Post
I've been wanting to try an MSD digital HEI module. As I understand it has a microprocessor or custom controller to trigger the charging and discharge of the coil, so dwell can be dynamic thru the rpm range, I think.

The other big thing is that it has a rev limiter. This would be really helpful for my trans am 4 speed that doesn't like over rev.

Can you give a mini lecture on how this module works?
Why not just get an MSD 6 box? It'll give you multiple sparks up until around 3,000 rpm and a longer, hotter spark after that. You dont even need a module with it and the box should have a rev limiter too ,depending on what box.
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Old 11-30-2017, 11:11 PM
  #85  
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Originally Posted by sc2dave View Post
Why not just get an MSD 6 box? It'll give you multiple sparks up until around 3,000 rpm and a longer, hotter spark after that. You dont even need a module with it and the box should have a rev limiter too ,depending on what box.
The trans am is almost completely stock and is worth more if I kept it that way. The MSD HEI modules are a stealthy mod.
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Old 11-30-2017, 11:21 PM
  #86  
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Originally Posted by turtlevette View Post
The trans am is almost completely stock and is worth more if I kept it that way. The MSD HEI modules are a stealthy mod.
Well, just take the box out when you decide to sell it , it's not a permanent modification.
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Old 11-30-2017, 11:29 PM
  #87  
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Originally Posted by turtlevette View Post
As I understand it has a microprocessor or custom controller to trigger the charging and discharge of the coil, so dwell can be dynamic thru the rpm range, I think.
it triggers the spark the same way a stock module does, only it allows the coil to produce a longer hotter spark, and it does not provide "dynamic" dwell, only a longer ,set dwell.The only thing you can adjust is rev limit. Here's from MSD site;
  • Easily installs to non-computer controlled (4-Pin) HEI housings
  • Built-in adjustable rev limiter can easily be set externally
  • Advanced dwell control for improved high rpm output
  • The Hottest HEI Module you buy-period!
  • Produces an incredible 8.5 amps of juice!
  • Adjust the rev limiter without removing the cap!
  • Fits in stock HEI distributors

Last edited by sc2dave; 11-30-2017 at 11:31 PM. Reason: added
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Old 12-01-2017, 07:11 AM
  #88  
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I had the MSD HEI upgrade kit. Car didn't run any better or worse with it. But I wanted a rev limiter and at the time it served that purpose. The better solution for anyone interested in proper tuning imho is a fully programmable ignition. This will allow a simple means to run higher initial timing and less mechanical. My initial is about 22* and 12* mechanical. Car purrs like a kitten and no nasty fuel odours.
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Old 03-02-2018, 09:09 PM
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Originally Posted by 69427 View Post
Okay, I changed my mind. There's a topic I want to discuss, and I think I'll let everyone digest the last (dry) post for a while, and do this one now.

A forum member asked me about coil overheating issues, and we discussed a few things that I think may be of interest to the collective.

Recall that I mentioned that the DC resistance in a coil is pretty much a byproduct of the wire size and length. What happens in a points ignition system if you mix and match coils?

Let's assume the alternator voltage is 13.2 volts, the dwell is 30* (out of 45*) and the original ballast resistor (assume it's a removable ceramic resistor rather than a ballast wire for this discussion) is 1.5 ohms, and coil primary winding has a similar 1.5 ohms.

At idle or low speed the coil primary current ramp up time is small enough to ignore for this discussion. So, the calculations:
The primary current is 13.2v/(1.5+1.5=3 ohms)= 4.4 amps. The ballast and coil resistive wattage numbers (I^2 x R) come out to (4.4^2)(1.5)=29 watts (instantaneous) on each component (because they're the same resistance). The dwell is 67% duty cycle (30/45) making the average power on each device 19.5 watts while the engine is sitting there idling.
Let's say the coil accidentally gets damaged, and is replaced by a generic parts store coil. You put your ohmeter on the primary terminals and find that the reading is 3 ohms. You know that the increased resistance in the system will lower the primary current (and energy), so you decide to bypass/shunt the ballast resistor to get back to a total of three ohms in the primary circuit. You hit the starter, and the engine fires right up. Success! Okay, lets see if anything actually changed in the circuit. The current (4.4 amps) is the same as before, and the system resistance (3 ohms) is the same, but now it's all in the coil, as the ballast is shorted out. Let's do the math. The resistive wattage is still (I^2)(R) so (4.4^2)(3)= 58 watts instantaneous, or 58 x (30/45) = 39 watts average. The careful observer will notice that the average power (dissipated in the coil) went from 19.5 watts to 39 watts (doubled!). Can the coil survive this continuous heating? I don't know. It depends on whether the coil can conduct away this heat, which is difficult to do when it is bolted to a surface that is 160- 200 degrees. Regardless, it's not a formula for reliability.
Third combination: Assume the parts store coil is one (1) ohm. We can do two things. Run it as is, knowing that the current will be higher [13.2/(1.5 + 1)]= 5.28 amps (hopefully the manufacturer has built in some safety margin, but good luck getting him to tell you what that margin actually is). The wattage in the coil will be 27.9 watts instantaneous, and 18.7 watts average. That's slightly lower than the original 19.5 watt baseline, so that should help offset the higher current concern a touch. (The corresponding wattage in the ballast resistor will be higher than the baseline though, and the reader can do the math if interested.) Second option is replace the 1.5 ohm ballast with a 2 ohm model to restore the current level to the original 4.4 amps if points life is a concern. The coil's average wattage in this situation is 13 watts. Directionally correct for increased component reliability.

So, two things: While most of the time we can swap coils around and not have the ignition fail on us while we're driving down the road, we are impacting the durability of the part (for better or worse) when the parts specs are changed. And secondly, with this new coil, did we increase the spark energy, or did we lose ground after spending our hard earned money? Unless we can actually get a direct answer from the manufacturer on what the inductance value is (or an honest answer of the calculated energy if you tell him what current level you're running) we won't know. You have to admit none of us would buy a cam or a set of tires if the manufacturer wouldn't publish the technical specs of the part they're selling.

More to follow.
I have an LT-1 with the stock solid state ignition. With the vacuum advance connected the timing becomes erratic at higher RPMs. I'd like to put the pointstype distributor in but with a Pertronix module and coil. Is this easy meaning will the standard distributor drop right in? Is it unwise? if so, why?
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Old 03-03-2018, 01:30 PM
  #90  
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Originally Posted by billyride View Post
I have an LT-1 with the stock solid state ignition. With the vacuum advance connected the timing becomes erratic at higher RPMs. I'd like to put the pointstype distributor in but with a Pertronix module and coil. Is this easy meaning will the standard distributor drop right in? Is it unwise? if so, why?
If you have a stock TI system, stick with it. Have it repaired.
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Old 03-03-2018, 01:41 PM
  #91  
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Why not get rid of points, shielding, resistors,etc and go withelectronic ignition? So much unreliability and problems with points. Just save the original parts to restore.
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