Changed Accel plugs to NGK iridium - more adv. possible?

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bigblockmopar
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Changed Accel plugs to NGK iridium - more adv. possible?

Post by bigblockmopar » Sun Oct 01, 2017 7:31 pm

Swapped over to Iridium sparkplugs today in my daily workhorse ('73 Dodge Dart w/318ci engine on Propane).
MegaSquirt3X controlling ignition only through a 7-pin HEI module and Blaster SS triggered by a stock Mopar distributor.

Sparkplug gap before and after was a little different;
Before with Accel 416 plugs: .026"
After with NGK iridium plugs: .036"

Old plugs still looked fine as I had cleaned them up a few months ago.
Didn't notice any change during driving, but tried rechecking the idle advance.
Engine always liked to idle in Drive at 500rpm with 24 degrees advance, where engine load was lowest and engine vacuum was around 20-21".

With the new NGK plugs, I found I could increase the advance upto 28-30 degrees and engine load would slightly decrease still (idling in Drive).

Now, I'll be back in a week and until then,.. Lol. just kidding. :)

Not quite sure what to make of this finding actually;
Did the engine/comb.chamber burn become less 'efficient' so the engine likes more advance now, or, do the NGK plugs simply let the engine's load be able to drop a little further with more advance, unlike with the Accel plugs, where idle-quality would become slightly less going over 24deg advance...?

Or did the increased sparkplug gap simply cleaned up things for the engine and let run with more advance and less load?

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Re: Changed Accel plugs to NGK iridium - more adv. possible?

Post by Amilcar » Sun Oct 01, 2017 7:38 pm

Did you got back to accel to confirm it indded happened due to the spark plugs?

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Re: Changed Accel plugs to NGK iridium - more adv. possible?

Post by bigblockmopar » Sun Oct 01, 2017 7:52 pm

No I didn't do an ABA test to confirm this, but I have tested/tuned this engine with the old Accel sparkplugs a few times before for best idle advance and it always came out to 24 degrees of advance which produced most vacuum or less load (kPa).

I only did a cranking compression test when all the old plugs were out and it netted a whopping 130psi...
(8.6:1 cr, stock cam).

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Re: Changed Accel plugs to NGK iridium - more adv. possible?

Post by Circlotron » Sun Oct 01, 2017 9:51 pm

bigblockmopar wrote:
Sun Oct 01, 2017 7:31 pm
Sparkplug gap before and after was a little different;
Before with Accel 416 plugs: .026"
After with NGK iridium plugs: .036"

Or did the increased sparkplug gap simply cleaned up things for the engine and let run with more advance and less load?
I'm with the bigger plug gap causing the change.
With a stock engine I always use .060" / 1.5mm if at all possible.

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Re: Changed Accel plugs to NGK iridium - more adv. possible?

Post by bigblockmopar » Mon Oct 02, 2017 4:32 am

With the previous Accel sparkplugs I tried a larger gap sometime ago but didn't notice much difference during daily use at the time.
To limit wear and tear on the rest of the ignition system I changed it back.
I recall limiting the gap even more down to the .026" when I was trying to find an occassional hickup during running, which turned out to be electrical noise making it to the MegaSquirt box which I could filter out.
I guess I never changed the plugs back to .032" again.


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Re: Changed Accel plugs to NGK iridium - more adv. possible?

Post by CharlieB53 » Tue Oct 03, 2017 10:13 pm

The fine wire tip of the iridium plug combined with the tapered ground strap may be giving a more consistent spark as compared to the larger tip and larger ground strap of the Autolite.

You will know more doing the ABA test.

You might consider a second test of gap sizing on the iridium, bringing spark voltage up closer to the limit if your system. Bigger/hotter spark etc..

I run the NGK Iridiums in most everything, compromised on the gaps around 45.

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Re: Changed Accel plugs to NGK iridium - more adv. possible?

Post by Geoff2 » Wed Oct 04, 2017 5:12 am

The fine wire plugs require less ark over voltage than the std plugs, due to a reduced quench effect [ that is electrical quench, not related to combustion chamber quench ].
The result is less misfires & longer plug life due to these very hard metals used for electrodes, which is why these plugs are used in modern engines: they are more reliable & go more miles.

A savvy hot rodder would run fine wire plugs & use a larger plug gap.

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