plug gap...what should it be? HEI

[old_skool]

No not stock silly, I have a service manual, but, I'm installing a HEI distributor in the next few days, will be bypassing the ballast(single ballast) but using the stock coil for now till I save up some more $$ for an upgrade there as well. My question is, would you increase your plug gap with the HEI or only after upgrading the coil...to what....040, .045, or ????
Should any modifications be made to timing also?

72 Charger 318 mildly built(unknown what actually) TorqueFlite auto with shift kit, possibly higher stall converter. Edlebrock 600cfm electric.

Thanks
Rich

 

[69Bee]

Start at 0.040", and increase the gap by 0.005" until the engine misses, then go back 0.005". I did this with my 426W, and using an Accel coil, gapped my plugs at 0.055" for best power.

 

[sleepar]

X2

 

[old_skool]

Can this be done with the stock coil, or should I wait till I upgrade?

 

[69Bee]

You could, but if you are going to replace the coil, why do the exercise twice?

 

[old_skool]

You could, but if you are going to replace the coil, why do the exercise twice?

Doing the double work doesn't bother me, as long as it's worth doing for run-ability wise/mileage etc

 

[paladin06]

So would this same rule apply for my 440 (1970)?

Start at 0.040", and increase the gap by 0.005" until the engine misses, then go back 0.005". I did this with my 426W, and using an Accel coil, gapped my plugs at 0.055" for best power.

 

[69Bee]

So would this same rule apply for my 440 (1970)?

This would apply to any motor. Factory specs are a compromise, and you can tune for best power or mileage. Cylinders fire best with the highest voltage possible, so by making the gaps larger, the coil builds up more energy before the plug fires. This is dependant of course, of how much voltage the coil is able to produce. A stock coil for a Mopar is NOT going to produce 45K to 75K volts, period. But, you can get it to function at its peak capacity ( about 17K to 18K volts if I remember correctly) by gapping the plugs larger. When the coil voltage cannot jump the gap, you will misfire, so you back it up about 0.005". An old or poor coil will breakdown sooner, so performance aftermarket coils work best. Accel and MSD used to be the hot ticket, but I am sure there are plenty more now a days.

 

[old_skool]

This would apple to any motor....

That's right...apples are ok, but apples and oranges are completely different...:urkidding: Just having some fun

 

[69Bee]

Son-of-A..... Late night post, LOL.

 

[old_skool]

hahaha, was just ribbing ya, picked up my wires, so, in a few......

 

[old_skool]

HELP
ok, need some direction...installed 8mm wires, had the distributor oriented I thought at 0 degrees, expected it to read there when I fired it up, gave me a lot of trouble starting, eventually started with a slight backfire, immediately double checked firing order, was correct, hooked up timing light, was approx 10degrees ATDC, unbolted distributor, set it approx 5 degrees BTDC, fired up a lot easier, no backfire, shut it off, restarted effortlessly, revved effortlessly, no backfire, took it for a test drive, ran ok but like a castrated dog, lost a lot of power, like I was pulling another car behind me.
Is this where the plug gap makes the difference, or is something else needing attention first. Idle is good and smooth.

I read somewhere on here where somebody had to move the cam gear one tooth due to the new distributor wasn't the same as the oem when it came to the contact in the distributor being aligned when at zero, I made sure the engine was at TDC and the cam gear slot for the distributor was pointing in alignment with the cam, had to fix that before, it placed my number one plug on the cap in a different place, but I wired it accordingly.

edit
Yes, I bypassed the ballast, and currently hooked to a ported vacuum. Have not opened plug gap yet, and is it possible the coil is old and unable to provide the necessary voltage needed for the HEI setup.

 

[1966satellite]

HELP
ok, need some direction...installed 8mm wires, had the distributor oriented I thought at 0 degrees, expected it to read there when I fired it up, gave me a lot of trouble starting, eventually started with a slight backfire, immediately double checked firing order, was correct, hooked up timing light, was approx 10degrees ATDC, unbolted distributor, set it approx 5 degrees BTDC, fired up a lot easier, no backfire, shut it off, restarted effortlessly, revved effortlessly, no backfire, took it for a test drive, ran ok but like a castrated dog, lost a lot of power, like I was pulling another car behind me.
Is this where the plug gap makes the difference, or is something else needing attention first. Idle is good and smooth.

I read somewhere on here where somebody had to move the cam gear one tooth due to the new distributor wasn't the same as the oem when it came to the contact in the distributor being aligned when at zero, I made sure the engine was at TDC and the cam gear slot for the distributor was pointing in alignment with the cam, had to fix that before, it placed my number one plug on the cap in a different place, but I wired it accordingly.

edit
Yes, I bypassed the ballast, and currently hooked to a ported vacuum. Have not opened plug gap yet, and is it possible the coil is old and unable to provide the necessary voltage needed for the HEI setup.

Did you disconnect the vacuum advance before you set your timing? I know you had to do that in the "old days"

 

[old_skool]

Did you disconnect the vacuum advance before you set your timing? I know you had to do that in the "old days"

yep, sure did, think I'm getting somewhere, adjusted timing some more, ran better, fooled around with ported and not ported vacuum timing, what I need is to find someone with a timing gun where you can dial in the timing, so I can check mechanical advance degrees with total advance and vacuum advance, and make the necessary adjustments to dial it in properly, and get a better coil, I'm sure once a better coil and plugs are gapped accordingly, it will run better. After my latest timing adjustment, not as anemic as it's closer to where it was before.