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I made these spark plug adapters to use the much better 3/4" reach spark plugs in big block heads(except the 452 heads with tapered seat plugs)that use 3/8" reach spark plugs in oem cast iron heads. The result is a modern plug design, that does not foul, faster cold and hot starts and more performance and gas mileage. These will fit any engine that uses the 3/8" reach plug including poly engines and early LA engines. These do work and are easy to install!
I made these spark plug adapters to use the much better 3/4" reach spark plugs in big block heads(except the 452 heads with tapered seat plugs)that use 3/8" reach spark plugs in oem cast iron heads. The result is a modern plug design, that does not foul, faster cold and hot starts and more performance and gas mileage. These will fit any engine that uses the 3/8" reach plug including poly engines and early LA engines. These do work and are easy to install!