Pelican Parts Forums - Opinions on twin plugging with race gas

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Chris,

Yesterday I e-mailed the NGK engineering staff with several specific questions and some general (philosophical) questions about sparkplugs and combustion chamber design. I’ll bet I don’t get an immediate reply but when I do, I’ll share the info. I’ll do the same with Bosch and Champion.

What does everyone think?
For street use in cool weather something like a NGK BP7ES up top (cooler head temp) and a BP8ES on the exhaust side, assuming two 14 mm plugs.

I have heard that some use only recessed plugs on the exhaust side.

All of the twin plug conversions of street heads that I have done used a 12 mm exhaust sparkplug. What is the current common practice?

Best,
Grady

I have the same size (14mm?) plugs top and bottom. I never thought about mixing ranges.
-Chris

There is extensive coverage of this topic in the Engine Rebuild Book. I suggest that you get a copy and read through Chapter Four. It explains all about Twin-plugging and what performance enhancements you can expect from it:

http://www.101projects.com

-Wayne