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P 51 spark plugs

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Post  Larry Williams January 23rd 2016, 11:10 am

What plug should I use with P51 heads?   heads as out of the box

flat top pistons   .010 in the hole       solid roller and a 1400 sv1 carb

14.5 to 1 comp ratio 545 cid
Larry Williams
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Post  rmcomprandy January 23rd 2016, 12:08 pm

Larry Williams wrote:What plug should I use with P51 heads?   heads as out of the box

flat top pistons   .010 in the hole       solid roller and a 1400 sv1 carb

14.5 to 1 comp ratio    545  cid

How is this engine to be used and does it have a closed exhaust system...?

I would probably use a #3910 Autolite with that compression ratio.

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Post  Larry Williams January 23rd 2016, 2:01 pm

a drag only engine with 2" headers
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Post  Rickytx630 January 23rd 2016, 7:02 pm

have a 514. 15:1 compression. p51 heads, qtf 1250 worked over. use autolite AR3933 plus, no problems. bracket car.

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Post  Larry Williams January 23rd 2016, 7:21 pm

Rickytx630 wrote:have a 514. 15:1 compression. p51 heads, qtf 1250 worked over. use autolite AR3933 plus, no problems. bracket car.

I have lots of those ty
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Post  rmcomprandy January 23rd 2016, 10:08 pm

A 514 at 15/1 will have a domed piston ... not a flat-top.
One plug is an extended tip and the other is not.

It will be a personal choice.

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Post  Larry Williams January 23rd 2016, 11:25 pm

rmcomprandy wrote:A 514 at 15/1 will have a domed piston ... not a flat-top.
One plug is an extended tip and the other is not.

It will be a personal choice.

is the 3910 an extended tip? Would it be ok to break in the motor with 3932/3933 then go with the 3910x ?
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Post  rmcomprandy January 24th 2016, 12:50 pm

Larry Williams wrote:
rmcomprandy wrote:A 514 at 15/1 will have a domed piston ... not a flat-top.
One plug is an extended tip and the other is not.

It will be a personal choice.

is the 3910 an extended tip?  

Yes ... I personally would use a hotter "street type" plug for initial running. Something like a 3924.

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Post  Larry Williams January 24th 2016, 5:33 pm

rmcomprandy wrote:
Larry Williams wrote:
rmcomprandy wrote:A 514 at 15/1 will have a domed piston ... not a flat-top.
One plug is an extended tip and the other is not.

It will be a personal choice.

is the 3910 an extended tip?  

Yes ... I personally would use a hotter "street type" plug for initial running. Something like a 3924.

I have a few sets of those too. I have to order the 3910's thanks for the info
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Post  Rickytx630 January 30th 2016, 12:30 pm

rmcomprandy wrote:A 514 at 15/1 will have a domed piston ... not a flat-top.
One plug is an extended tip and the other is not.

It will be a personal choice.

JE flat tops. no domes in my motors.

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Post  rmcomprandy January 30th 2016, 1:50 pm

Rickytx630 wrote:
rmcomprandy wrote:A 514 at 15/1 will have a domed piston ... not a flat-top.
One plug is an extended tip and the other is not.

It will be a personal choice.

JE flat tops. no domes in my motors.

A 514 with a flat-top piston at "0" deck, #1018 head gasket and a 70cc combustion chamber is about 13.4/1 compression ratio.

The heads would need to be milled near 60 cc's to be at 15/1 compression.

Your personal choice is to use non-extended tip spark plugs; there is not an actual NEED to do so.

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