Need a spark plug 1 step hotter than a NGK r5671-7 ? Ngk doesn't make a -6.
Need not be NGK for a street machine 440
Thanks

Is that a stock type iron head with a OEM type spark plug or a 3/4 inch SB type plug with the 5/8 inch socket size?
If stock try a Champion RJ10YC or a RJ12YC or a Autolite #84 or 85.
If it is the smaller 5/8 socket size with the 3/4 inch reach try the Autolite # 23 or 24
IHTHs

NGK R5671-7 crosses to an Autolite 4054. Autolite does a 4055 and 4056 - 1 and 2 steps hotter. Standard non-resistor, 3/4 reach, 13/16 hex. 4056 is equivalent heat to the old 64.

Not to get off topic, but is the a site that a guy can go to that shows cross reference on multiple plug manufacturers? I looked the other day and had a real hard time crossing some. Jim

what cylinder head? I use autolite 3926's in edelbrock heads.

NGK does make a #6 plug..........Like asked, cyl. head makes all the difference but here's a number that looks like it should work for an aftermarket head....R5674-6 or 4449 stocking number..

Thanks for the info for alum edelbrock heads.

I don't think you can use a 3/4 reach spark plug with the stock 13/16 plug socket size, I'm almost positive you need to us the smaller 5/8 socket size plugs Champion plug numbers RN9YC versus a RC9YC.
Autolite resistor plug # in 5/8 size I use are 3921 and up to 3924 in my race gas motors and the same 5/8 size in non resistor # in retracted gap are 3931 to 3935, 3931 is very cold.

partial xref

That 4449 nil is not a 3/4” reach plug if that’s what’s needed. I bought a set, not sure I can use those being 7/16 reach

One step hotter than a “7”, but they have a projected tip:

BCP6ES

Or

BCPR6ES

Thanks Dwayne. I believe the BCP6ES is a resistor plug. I like to run the non resistor type.

for my aluminium head 440s I use a NGK BKR6E

Tex