T-350 Transmission Fluid Type?

Yes Craig, it has a B&M full Shift Kit and some "Hardened" parts inside that I can't remember what they are. The 455 Olds is using a B&M Holeshot 2400 converter, 3.73:1 posi. Runs consistent 7.6 sec in the 1/8 mile and has run 11.3's / 115 mph when we had a 1/4 mile track (Fontana).

Pick a fluid that is inexpensive and readily available. Keep it clean, keep it cool and keep it full. That's the main thing no matter what you decide to run.

Just for the heck of it, here's a little data dump for consideration...or amusement. Keep in mind that Bogie and Stuart A have both probably forgotten more about this stuff than I will ever know.

My understanding of Wet Clutch Application consists of 3 Phases:
Phase 1 - Low Pressure Oil Sheer. The oil trapped between the friction and steel absorbs rotational energy and converts it into heat.
Phase 2 - High Pressure Oil Sheer with an Ordered Boundary Layer. This thin trapped layer of oil is essentially functioning as a Syncro Ring. The friction and steel are not in contact.
Phase 3 - Slip-Lock. Where the Friction and Steel finally meet.

It all happens quickly and what happens in each phase is what went into development of a particular type of transmission fluid. Clutch material and size along with their applications for use dictated what was needed in terms of managing the friction coefficient at different points.

Ford developed Type F for the asbestos clutch. Their aim was reduce the dynamic (moving) part of the application and to enhance the static (locked) part of the application.

GM had the opposite aim in their development for the paper clutches. They were enhancing the dynamic part without facing the same static dilemma Ford had.

Generally speaking, Dexron is going to perform better dynamically and Type F is going to perform better statically. Clutches are very different these days. With the clutches that perform well dynamically (grooved, waffle, waved, graphite, etc.) some builders prefer the static enhancing Type F. Other builders like the Dexron because these clutches also perform well statically and they like the dynamic enhancing Dexron.

Running Type F in a GM transmission will produce a different feel. The Dexron is a more even application and the Type F is less even, doing more right at the end (the positive shift feel). Debate will rage on until the apocalypse about which shift is actually better or faster.

Modern fluids have to be VERY balanced in their friction coefficient to keep torque converter clutches happy. A little off in either direction = the dreaded torque converter shudder.

Did you perform any modifications to your transmission(s) or are you only using the ATI fluids?

GM Dexron is used for soft mushy shifts, I put Ford type F in my GM builds from ATI, comes in 0W-8, 20 or 30 weight. It’s expensive!

0W-8 is pretty good for street shifts, it you want more bang on the shifts either 20 or 30 is brutally positive.