The stock 5/16" O.D. metal fuel lines have been known to support up to 500hp, but
we recommend stepping up to large fuel lines when you surpass the 400hp level.
Why stress your fuel pump unnecessarily if you can run large fuel lines?
-6 AN stainless steel line is good to 600hp, and you can keep the stock metal return
fuel line. You can step up to large AN SS lines, but keep to the rule of
thumb of using "one step down" on the return line; -8 feed -> -6 return; -10 feed ->
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