350 Chevy Engine with HEI- Spark Plug Gap?

[rally]

Guys running a high performance HEI Distributor in my 72 Nova SS 350 Engine. Using a Autolite Plug 145. What spark plug gap would be best for all around Street Performance on this Engine with a 10-1 Compression, World Heads, Etc? Best gap?

[jimjamm65]

.045"

[Tuner]

.035" is enough. Wider gap just results in more rapid deterioration of the HV parts, coil, rotor, cap, wires, etc. Testing back in early days found wider gap may reduce fuel consumption. Your mileage may vary.

[psychomotors]

I would shoot for .040 - .045 IMHO. Google search showed pretty much the same as my thoughts.

[Carnut1]

I have run wide and narrow gaps. Now I am old I just run .035" I think it helps idle and is easier on wires. Jmo

[rally]

035 Thous sounds good.

[Baprace]

We do a lot of high compression stock ignition circle track 2bb carb engines and we find that .032 - .035 works very well with OEM HEI distributor systems on gasoline.

[Geoff2]

I run 0.060" with 10:1 CR. Mate runs 0.070" with 11.3:1 CR, he uses Platinum plugs which require less arc over voltage. Both street driven & registered, mate drag races. I ran 0.100" gaps to see what would happen; ran/started just as well, no discernible difference, went back to 0.060" gaps.

Common sense tells me that the greater the plug gap, the greater exposure the mixture gets to the heat of the spark, the heat in the spark being what ignites the mixture. Within the bounds of the ign system. The Bosch [ Australia ] HEI system specified 0.065" plug gaps on engines with well over 9:1 CR.

If small gaps were best, we would still be running magnetos with 0.020" plug gaps...

[user-23911]

Bigger gap means a quicker burn so less advance required, with that comes less losses from compressing an already burning mixture. Less likely to knock too.
More capacity in the ignition system = better.


I've never heard of anyone going out to .060 gap but it makes sense.


I run stock gaps(1.1 mm platinum) in my turbo japper at increased boost.
I can only do that because I've doubled both the energy and voltage capability (60KV) of the stock ignition.

[Geoff2]

Joe,
I am always interested in how to get more spark energy. Care to share how you did it? I currently am running the MSD HEI 7.5 amp 4 pin module, mounted under the dash to keep it cool. Also run the MSD 8207 E core coil, remote mounted.

[user-23911]

It's really simple, double the number of coils.
Use double ended coils (eg mitsubishi wasted spark type, they're limited to about 7A each with the proper driver unit ), wire the secondaries in series, primaries in parallel.
Use junkyard parts.
Cost = zero.

like here

https://www.youtube.com/watch?v=fL4runxvX_I

It'll never catch on because there no money for anyone to make from it.

There's no limit to the number of coils you can daisy chain together.
You could use 3?
Like here

https://www.youtube.com/watch?v=2ig8wQ9uRvc

But ideally you'd want to get rid of the distributor first.
The cap would be the weak point.
I've had it running for a few years now but as wasted spark.


If you're too scared to experiment, you won't get anywhere.

[Truckedup]

It's really simple, double the number of coils.
Use double ended coils (eg mitsubishi wasted spark type, they're limited to about 7A each with the proper driver unit ), wire the secondaries in series, primaries in parallel.
Use junkyard parts.
Cost = zero.

like here

https://www.youtube.com/watch?v=fL4runxvX_I

It'll never catch on because there no money for anyone to make from it.

There's no limit to the number of coils you can daisy chain together.
You could use 3?
Like here


https://www.youtube.com/watch?v=2ig8wQ9uRvc

But ideally you'd want to get rid of the distributor first.
The cap would be the weak point.
I've had it running for a few years now but as wasted spark.


If you're too scared to experiment, you won't get anywhere.

I'm interested.... Show diagram of several waste spark coils wired as you mentioned and an installation on your vehicle......Doubled ended waste spark coils are not designed to fire two spark plugs during the compression stroke...Many have tried this when dual plugging bike heads and it just doesn't function...

[Circlotron]

I've never heard of anyone going out to .060 gap but it makes sense.

Blue 202 in VC & VH Commodore. Factory spec gap.

[user-23911]

I'm interested.... Show diagram of several waste spark coils wired as you mentioned and an installation on your vehicle......Doubled ended waste spark coils are not designed to fire two spark plugs during the compression stroke...Many have tried this when dual plugging bike heads and it just doesn't function...

you're doing it wrong.
It's too easy to need a diagram.

A double ended coil is an isolating transformer.Because of that, you never get insulation breakdown, unlike COP coils which are extremely unreliable, they suffer shorts to the earthed tube.
The 2 posts are secondary pos and secondary neg. 2 ends of one coil.
One coil normally fires 2 cylinders (360 deg out of phase) but only one cylinder has fuel and is compressed, the other is exhausting.
The exhausting cylinder loses at the most maybe 2 or 3Kv across the plug due to low pressure.The rest of the energy goes to the plug that's required to fire.
All you're doing is adding a second pair of HT terminals in series so it's pos of one coil to neg of the other coil, the other 2 terminals go to the plugs.

Like here.

https://www.youtube.com/watch?v=QGNcQicVONg

The advantage is that if one coil fails , it still runs on all cylinders but at lower voltage.

[Truckedup]

Joe, I understand that....But it it a power advantage or just more complicated...maybe some showing speed on a track or more power on a dyno as compared to a more conventional system...