please help with spark plugs for high compression 347 build!

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Jun 8, 2013 | 12:59 PM

midwestjunk

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From: Addison, IL

please help with spark plugs for high compression 347 build!

My buddy just bought a 01 ws6 with a forged 347 short block, ls6 heads and direct port nitrous. its 12.5:1 compression. so the plugs in the car when we bought it were for running on motor. they are NGK UR5. I assume its not a tr55 or tr6 because of the domed piston would hit something with that long of reach. so we need a part number for a plug that is 2 steps colder than stock, with the same reach of this UR5 but in a non projected tip. anyone know anything about NGK part numbers. or someone with a similar set up spraying with a big domed piston with short reach plugs. any help is appreciated.

Jun 8, 2013 | 03:28 PM

midwestjunk

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From: Addison, IL

I may have found something....Will a NGK R5673-9 work? Anyone run this plug?

Aug 27, 2013 | 01:39 PM

Killer5.3

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From: Ms

Quote:

Originally Posted by midwestjunk

I may have found something....Will a NGK R5673-9 work? Anyone run this plug?

Yes it should work , but, it isn't tapered seat. Should have washer. I would thread each plug in an old cylinder head first to seat it and crush the washer and then install them in the engine. Make sure and put some antiseize on the threads. I would gap them .026-.028.

Aug 27, 2013 | 07:35 PM

dr_whigham

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From: Lafayette, LA

BR7EF, non projected tip

Part # 3346

Last edited by dr_whigham; Aug 27, 2013 at 07:40 PM.

Aug 27, 2013 | 09:15 PM

Grr

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From: Fargo ND

R-5724-8
That is what I ran on my 14.5:1 346 and what I run In My 12.5:1 ls3

Jun 27, 2021 | 10:07 AM

Vadim Todorov

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From: Hutto TX

Quote:

Originally Posted by Grr

R-5724-8
That is what I ran on my 14.5:1 346 and what I run In My 12.5:1 ls3

Don't mean to side track the post, what fuel did you run in 12.5:1 LS3? I finishing a 12.5:1 LQ9 with LS3 heads. I was planing to run E85 (vition fuel lines a and all) but wondering if there better options in that do not have the E85 disadvantages .

Jun 27, 2021 | 10:22 AM

01CamaroSSTx

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From: Conroe, Texas

Old thread and I'm pretty sure most of these people are long gone but as fuel goes there's MS109 which is unleaded and you have C12 and C16 which are even higher octane fuels but are leaded. They all cost more than E85 so what are the disadvantages of running E85? I get it with M1, it takes even more fuel injector and pump for it but if running high compression and adding boost then it would be my go to fuel.