What Plugs for 327 with HEI - Impala Tech
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post #1 of 5 (permalink) Old 07-17-2012, 07:13 PM Thread Starter
 
 
Join Date: Jul 2012
Location: Fort Mohave, AZ
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What Plugs for 327 with HEI

I just bought an HEI Distributor for my 1968 Impala with a stock 327 (275 HP) Motor...was wondering what plugs would be best it was running the AC Delco R45S copper plugs (what came in it when I purchased the vehicle)...I will change wires to HEI Silicon High Heat wires also...but in a quandary as to what plugs to use...I would have kept the stock distributor, however it was well used and pretty shaky...and in our heat out here in AZ, any thing you can do to make for as little break downs is greater than my feelings on keeping the vehicle exact to spec... anyway having said that has anyone done this and with this specif motor, and what plug did you have good experience with, and any other help on the switch please let me know
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post #2 of 5 (permalink) Old 07-17-2012, 07:34 PM
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Plug stays the same. You just open up the plug gap a bit more (about 0.020" more than what it is now) to 0.055" to 0.060" of an inch.

I like spiral wound 8 mm MSD or Accel spark plug cables but with their garish colors they don't look stock.

Big Dave
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post #3 of 5 (permalink) Old 07-17-2012, 07:53 PM Thread Starter
 
 
Join Date: Jul 2012
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I don't know Big Dave at my age garish is just a way of life...I do love my Hawaiian Shirts...LOL...thanks for the tip I will go with the wider gap and try the 8mm Accel wires thanks again
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post #4 of 5 (permalink) Old 07-17-2012, 08:31 PM
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Dave, why then do early HEI engines across the board call for a say .45 gap and later HEI engines go as high as .70? Combustion chamber design, compression? Don't most stock HEI joules fall off above 4K rpm's?
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post #5 of 5 (permalink) Old 07-18-2012, 08:32 AM
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Quote:
Originally Posted by 68imp View Post
Dave, why then do early HEI engines across the board call for a say .45 gap and later HEI engines go as high as .70? Combustion chamber design, compression? Don't most stock HEI joules fall off above 4K rpm's?
Yes and yes.

Transistor technology discovered in 1956 and developed by the military in 1958 was first used in cars back in 1966 in the radio. It has continued to evolve from individual macro components to microscopic printed circuits. So yes you are correct in that the newer aftermarket HEI modules out puts a hotter spark than the older stock units that were unreliable. The reason they were unreliable is because of heat build up. Modern technology is much more heat resistant and they are more efficient so they do not generate as much heat to begin with. That white grease that dried up is a heat conducting path for the HEI module and is the reason most failed early.

The problem with the spark power falling off above 4200 RPM has nothing to do with the transistors and everything to do with dwell time. The ignition coil (your flux capacitor that keeps your old time machine running) is nothing more than a transformer. It takes an infinitesimal small, but finite period of time to saturate the steel and build up the magnetic field strength in the core (mostly because of the cheap steel they use for the core). Above 4200 revolutions per MINUTE there isn't enough time to saturate the coil so the spark gets weaker at higher and higher RPM's. This is why new cars have one coil for each plug so the ignition spark has more time to generate a hotter spark.

A capacitive discharge system charges faster than an inductive system which is why all race cars have them under the hood. Install bigger caps and you get a bigger spark which is why they have a 6, 7 and a 10 nomenclature across the board on picking how expensive an ignition box you want to buy. Note that they still rely upon a coil to fire the plugs. The difference is the primary side of the coil with an ignition box sees more energy going into the coil at the start of each cycle so that the out put is greater on the secondary side. A more expensive E-coli made out of a high silicone content alloy steel is used in the aftermarket to make a faster charging hotter out put coil.

So great is the difference with an ignition box instead of an HEI is that the plug fires not once, but multiple times below 4200 RPM for easier starting and better fuel mileage. The higher you spin the motor the less time there is for the multiple spark feature to fire so that the number of ignition pulses drops off from as many as four strokes at idle to only one at 4200 RPM and above.

Big Dave
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