Spark plug recommendation for aluminum headed big block ford

[The_Eric]

I have a customer that has a 514 Ford with aluminum heads and mild cam/compression. The builder originally used an Autolite AR3934 plug which looks super cold. Carb tuning issues aside, I'm not convinced that he needs a super cold plug.. I'm thinking something similar in heat to an AC 43.. how does this AR3934 compare? I've looked around the net a bit and I'm having a hard time separating it from all the cold racing plugs, but did manage to use the NGK chart and to piece together a number (BKR9EIX) and cross it back to the AR3910 I think. There are also a couple NGK racing numbers R5671A and R5672A but I don't really know their heat ranges in comparison to what I'm familiar with...

What I need is 14mm thread with a .750" reach and a 5/8" hex.

 

[PontiacHO]

If it is a street car/cruiser and has a choppy cam and rich carb then a warmer plug is needed. Does it have a distributor with vacuum advance or a programmable distributor for advance at idle? Race car timing setups with no advance don’t work well for cruisers. Get the timing right before tuning on the carb also. Most cams need 16 to 18 degrees initial and all in total of 32 to 36 degrees by 3600 RPM. That’s a pretty standard starting point anyway.

 

[The_Eric]

If it is a street car/cruiser and has a choppy cam and rich carb then a warmer plug is needed. Does it have a distributor with vacuum advance or a programmable distributor for advance at idle? Race car timing setups with no advance don’t work well for cruisers. Get the timing right before tuning on the carb also. Most cams need 16 to 18 degrees initial and all in total of 32 to 36 degrees by 3600 RPM. That’s a pretty standard starting point anyway.

I haven't gotten the car yet - but I plan on baselining it. The engine was built by a sort of local machine shop but installed by my customer and his son. They're well intentioned but I think that they're lacking in knowledge. For sure I want to check timing and I'm generally pretty good with Holley type carbs (this is a Quick Fuel clone). It's in a 70 something Ranchero that will be mostly a cruiser that may see trailer hitch duty from time to time.

 

[PontiacHO]

Sounds like an interesting project. Keep us posted on your progress. Sometimes the local machine shop guys are really good at attention to detail. They have to keep a business alive…