E85 + Boost, what plugs?

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subcom

subcom

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What spark plug would you guys recommend? I've read a few threads on the turbo forums and YB. Lots of folks recommend NGK and a non-projecting tip in a heat range between 7-10, 10 being the coldest. Anybody have a part # they've had good luck with? Mine is an iron headed 5.9 magnum, stock compression, E85 and about 8psi max. Also, what gap? I currently have an HEI ready-to-run setup and have my Autolite 3924s gapped pretty wide at ".045"
Thanks!
 
I was currently running these https://www.summitracing.com/parts/ngk-4091/overview/ with about 10psi of boost. Then a very reputable performance shop said I should be running at least a 9 heat range if I'm boosted with a carburetor. I need to do some more research about heat range with carbs vs FI before I make the switch. And yes, that is way too much gap for forced induction. Tighten that up to .030-.032.
 
chargd72 said:
I was currently running these https://www.summitracing.com/parts/ngk-4091/overview/ with about 10psi of boost. Then a very reputable performance shop said I should be running at least a 9 heat range if I'm boosted with a carburetor. I need to do some more research about heat range with carbs vs FI before I make the switch. And yes, that is way too much gap for forced induction. Tighten that up to .030-.032.
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Thanks for the feedback. That NGK you use is specd very similar to the one I chose, so hopefully I'm on the right track. Mine have resistors though. Didn't want to risk ECU interference from a non-resistor plug. I think 7 heat range is a good starting point for a car that gets some street mileage also.
 
How did those plugs work out? I have a very similar setup only FItech EFI on a W2 iron headed LA motor. I'll be starting out with somewhere between 5-8PSI (guess work based on the s/c pulley).
 
I ended up going with a colder Autolite. 3922 I think? Gapped at 0.030. The original one in my first post was too wide to fit in the socket well if my heads.
 
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