spark plug selection

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spark plug selection

Post  BUZZ BUZZARD on October 23rd 2012, 8:29 pm

Looking for spark plug suggestions I now run ngk R5671A-7 plugs. Engine is 557 tfs streets flat tops .738 lift cam 34* timing block decked to 0. Am I in the correct range ? go hotter? go colder? car runs on c-12 race gas.

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Re: spark plug selection

Post  Lem Evans on October 23rd 2012, 8:42 pm

I suspect that a "8" would be better per your application.
"""""""""""""""""" "9" would not be an issue.


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Re: spark plug selection

Post  BUZZ BUZZARD on October 24th 2012, 9:19 am

Thanks Lem the 7's seem want to foul easily. EGT's are around 1380*, tryed to jet up to 94's but engine would not want to rev. Went to 90's car picked up but egts also went close to 1400.

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Re: spark plug selection

Post  Lem Evans on October 24th 2012, 11:10 am

The "7" is warm for your application.......they should not be fouling. Maybe the idle circuit is rich or weak ignition?

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Re: spark plug selection

Post  BUZZ BUZZARD on October 24th 2012, 7:17 pm

I had my numbers crossed up I thought a 7 was on the cold end on an ngk. The plugs could have gotten fouled when the carb had powervalves and overjetted. I was having so many other issues with the car that I never took the time to change the plugs after some major carb tuning and going from c-16 fuel to c-12. I have two new sets of autolite ar3933 that I found in one of the cabinets in the shop. They were for a friends 427 small block that I built a while back. They are two steps colder then the ngk 7. Any suggestion on optimum gap?

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Re: spark plug selection

Post  Lem Evans on October 24th 2012, 7:20 pm

The side gaped AR3933 do not require a lot of gap...... .025"ish will work.

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Re: spark plug selection

Post  Lem Evans on October 24th 2012, 7:22 pm

BUZZ BUZZARD wrote:I had my numbers crossed up I thought a 7 was on the cold end on an ngk. The plugs could have gotten fouled when the carb had powervalves and overjetted. I was having so many other issues with the car that I never took the time to change the plugs after some major carb tuning and going from c-16 fuel to c-12. I have two new sets of autolite ar3933 that I found in one of the cabinets in the shop. They were for a friends 427 small block that I built a while back. They are two steps colder then the ngk 7. Any suggestion on optimum gap?

The Jap plugs are backwards.......bigger # = colder.

Champion and Autolite.....bigger # = hotter.

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Re: spark plug selection

Post  BUZZ BUZZARD on October 24th 2012, 7:32 pm

Thanks for the info.

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