4L70E Cooler Line Size

[572Camaro]

My 68 Camaro utilizes a 4L80E.
I like hardline stainless.
I ran 5/16” diameter Swagelok 316 alloy SS.
5/16” may sound small but I got that direction from Gordon Stoney who was supervising engineer for Hydromatic Division at GM.

I autocross (not very good at it) and “spirited driving” on the street.
Mark Bowler sold me the transmission case fittings from Sonnix and he knew I was running 5/16” lines with no worries.

CONCERN: make sure you get the proper trans case fittings because, at least for my 4L80E, the rear fitting has a nozzle that lubricates rear spider gears. No nozzle = burnt gears! I learned this from Mark Bowler.

If you go flex, please get PTFE.

Thanks and best of luck