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HEI conversion


72 Monte Carlo

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I'm almost ready to fire up my 396 stroker motor that I built for my 72 Monte Carlo. The car had no motor when I bought it last year.

I got a brand new HEI distributor, plug wires, and spark plugs for the install. I read that I should run a 12 ga wire from the ign spade in the fuse box to the BAT on the distributor. For an in dash tach install, is there a certain color wire that was existing to the old style coil that I can use for a factory style tach, or is there a certain way to wire it up from the dash?

Also, I disconnected the factory external voltage regulator on the core support so that the "generator" dash light would go out when the ignition key was in the off position. I got a GM 1 wire alternator for the car, so is there something special that I need to do with the wiring to the old voltage regulator to make sure things are working properly.

Thanks,

Doug

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My 71 is still all stock so I have not done any changes. Many people have mentioned this web site for charging system information and changes.

http://www.madelectrical.com/electricaltech/chevymain1.shtml

I have read about using a 10 gauge wire for a GM HEI system not because it draws lots of power but because of ? interference / signal disruption or something like that.

Good luck!

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Hi, Doug,

I can't help you with your alternator or voltage regulator questions but I can tell you what worked for me when I converted to an HEI distributor with a factory tach in the dash. 

The tach wire is brown and simply moves from your old coil over to the tach port on your HEI distributor.  If I remember correctly, I had to crimp a new female spade connector on the end of the brown wire to properly plug into the tach port which is a male spade sticking down inside the connector box on the driver's side of the HEI.  In the second photo below of the HEI unit, the tach port is just outboard of the connector already plugged into the connector box near the lower right corner of the photo.  (see photo below)  Unfortunately, I am over 1,800 miles from that Monte right now so I can't confirm my recollection.

I had also heard the recommendation to run an independent 10 ga twisted copper wire from the IGN port in the fuse box directly through the firewall to the power port on the HEI.  It is the fat red wire with the light blue shielded connector plugged into the IGN port of the fuse panel in the lower right corner of the first photo below.  I did not make any changes to the alternator or voltage regulator during the distributor swap.

P5155437.JPG

P1124555.JPG

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Ten Ga. wire is a better choice.  The factory wire is sized for the average current and disregards the peak voltage drop of the "Pulsed" coil primary.   So the average current is what the factory wire size is determined by, but the peak current losses are what needs to be limited for maximum performance.  Keeping in mind the average current in the wire is determined by RPM's and the peak current is always determined by wire resistance and the dielectric resistance of the compressed fuel/air mixture.

The voltage drop across the wire during the "Pulse" is calculated by peak current x peak current x wire resistance.  The peak current losses (Voltage drop) will be the same every current pulse but the average losses (Voltage drop) will increase with RPM's.

minimizing the wire length and resistance (Thicker wire/smaller Ga.) from the HEI to the coil primary will give you the strongest spark.  The thicker Ga. wire has lower resistance and becomes more critical as the compression of the motor increases.   The higher the engine compression the greater the "Dielectric resistance" of the fuel/air mixture becomes...  so a smaller gap at the plugs and increased wire Ga. and minimum required wire length becomes more significant...  Higher the compression the higher the dielectric resistance and the smaller the gap should be.

If you use crimp lugs I recommend "Tinning" the wire with a soldering iron prior to crimping, then after crimping the tinned wire in the lug, solder the crimped wire to the crimped lug.  The slow effects of corrosion will take it's toll in time, increasing the voltage drop as the inevitable oxidation occurs.  So, the normal (Untinned) wire to crimp lug connection, in time, will exceed the wire resistance losses and slowly degrade the spark.  Also, when tinning the wire, make the solder go to the heat, place the solder iron on the tip of the wire and place the solder near the insulation and the solder will wick towards the iron and wont migrate under the insulation of the wire.  

john

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When I went to a one wire Alt. two years ago I jumped the the two out side wires and the inside wires on the plug and everything works fine. I just tucked the wiring up under the fender behind the washer jug.

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Thanks for the info!

I was able to get under the dash and the previous owner had a nice 10 ga wire already connected to the IGN terminal in the fuse block, so I routed that out through the firewall and connected it to the HEI. Now I just have to modify the external voltage regulator wiring as Leghome suggested.

Thanks again!

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The single wire versus the 3 wire alternator essentially means that the voltage regulator "Senses" the voltage level at a point downstream of the alternator, versus right at the alternator.  For low current draws systems (No fans or electric fuel pumps or a high wattage stereo) this is not a problem.  What can be done is reducing the wire losses between the 1 wire internal regulator to the distribution/fuse panel for the the DC distribution.  for the 1 wire alternator a heavy Ga. wire to the fuse panel will decrease the drop in voltage in the wiring and the local regulator on the alternator will do a better job with only a 1/4 volt or so difference between the regulator sensing the voltage at the alternator compared to a 3 wire sensing the voltage at the distribution point... Make sense??  decreasing the voltage drop to the electrical loads will be as effective as 3 wire remote regulation.....

 

john

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