Spark plug recommendation

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Illahe

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Hello all,

In need a spark plug recommendation for a 340 fired by a 7Al-2 ignition module. 10:1 compression. I assume the oem plug is not sufficient. Gap, brand ect.

Thanks,
 
Illahe said:
Hello all,

In need a spark plug recommendation for a 340 fired by a 7Al-2 ignition module. 10:1 compression. I assume the oem plug is not sufficient. Gap, brand ect.

Thanks,
Click to expand...
What makes you think the stock plug is not sufficient? Early stock 340s were 10.5:1 (allegedly). .032-.035 gap, I like Autolites. Start with a 65, adjust the heat range as required (learn to read the plug).
BTW, this is with stock LA heads- not Magnum heads or some aftermarket head that takes an oddball plug style.
 
Professor Fate said:
What makes you think the stock plug is not sufficient? Early stock 340s were 10.5:1 (allegedly). .032-.035 gap, I like Autolites. Start with a 65, adjust the heat range as required (learn to read the plug).
BTW, this is with stock LA heads- not Magnum heads or some aftermarket head that takes an oddball plug style.
Click to expand...
Correct on the La head. Finishing the assembly at this time and need to order a set of plugs. I presumed the hot ignition may require a different plug due to the large gap, as the Ignition manufacture recommended .050-.060 gap for 10.5:1. And the ignition set up is new to me.

As for the Autolite 65, I have no issue, having run them 35 years ago with a Unilite distributor and a Mallory coil.
 
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NGK GR4 Spark Plugs
V POWER

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Running ^ .050 ths gap, e-core coil 60,000 volt, hei ignition.

Timing is set back to 10° BTDC (from 12° BTDC) because the high energy ignition burns so fast, it needs to be backed down to fall into the factory specs.


☆☆☆☆☆
 

Professor Fate said:
What makes you think the stock plug is not sufficient? Early stock 340s were 10.5:1 (allegedly). .032-.035 gap, I like Autolites. Start with a 65, adjust the heat range as required (learn to read the plug).
BTW, this is with stock LA heads- not Magnum heads or some aftermarket head that takes an oddball plug style.
Click to expand...

George Jets said:
NGK GR4 Spark Plugs
V POWER

View attachment 1716435731

View attachment 1716435734

View attachment 1716435735

Running ^ .050 ths gap, e-core coil 60,000 volt, hei ignition.

Timing is set back to 10° BTDC (from 12° BTDC) because the high energy ignition burns so fast, it needs to be backed down to fall into the factory specs.


☆☆☆☆☆
Click to expand...
Thanks for the input!
 
I would normally recommend the NGK '4' heat range, but the 7AL is CD ign, so I would use the '5' heat range, one step colder.
 
The 'source' is the fact that the 7AL is a CD ign system. The engines in question use inductive ign. CD ign has extremely high energy in the spark, but is about 1/10 the duration of an inductive ign spark. So the CD spark timing sometimes needs to be retarded so that the completion of the burn occurs at the correct crank angle.
 
id suggest the cheapest you can get until you get it nearly tuned then get a nice set.. avoids ruining a nice set

i bumped CR from 9:1 to 12:1 and went from NGK 5 to NGK 7... the engine running in its new home will let you know....

Dave
 
I just did the Edelbrock top end kit on my 360 with 6al MSD. To be safe (better to be too cold) I put in NGK 7. They are way too cold. I will go to 5.
 
Bewy said:
The 'source' is the fact that the 7AL is a CD ign system. The engines in question use inductive ign. CD ign has extremely high energy in the spark, but is about 1/10 the duration of an inductive ign spark. So the CD spark timing sometimes needs to be retarded so that the completion of the burn occurs at the correct crank angle.
Click to expand...
i wasn't addressing you.

if i was, i would've quoted you.
 
I recommend running spark plugs. Engines generally run better with them than without.
 
I run 65’s at 12.2 and .039 gap. I like they are cheap and can change them at a whim. I buy every one they have in stock. Around $3.00 each? Plus the old ones work in my lawn tractor and other yard equipment….
 
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