My 69 firebird has original motor and transmission. I cant figure out why it came with a 400 transmission with a 350 motor?

I figure a 350HO would come with a TH400. But I'd guess that a TH400 with a 2-barrel 350 would be an extra cost option.

Not sure, but I assume that some 2-barrel 350 1st gens came with a ST-300, & some came with a TH350. Maybe a PHS report would tell you how it was originally ordered.

Option? 2 or 4 bbl?

If a 1969 Firebird 350 was ordered with a 3-speed automatic, you would get a TH350 if the car didn´t have A/C. If the car had A/C, you would get a TH400. I can't figure out the reason why, but that's how Pontiac specified the cars.

So are you saying that you could not get a TH400 with a 350HO, unless the car had A/C, but that all 350 2-barrel engines could get a TH400, if the car had A/C ???

Just curious. Where did you get this info ? Post a link to it please.

You have to have a 400 engine to get TH400 trans

That is for '68 Birds. The OP has a '69.

I think the '69 350HO got a TH400.

https://www.hemmings.com/magazine/mus/2016/06/1969-Pontiac-Firebird-H-O-/3749792.html

Sorry, my information above was apparently only valid for 350 2-barrel Firebirds.

If we only look at 1969 350 engines and 3-speed automatics, the 1969 Pontiac Service manual (Shop Manual) says that the TH350 (or M38) trans would be fitted to 350 2-barrel except A/C (transmission code JF). It's on page 7G-1 in the manual.

Page 7E-2 in the same manual says that 350 2-barrel cars with A/C would get a TH400 (or M40) with code PV, and a 350HO would get a TH400 with code PS (regardless of A/C or not).

I still can't figure out why Pontiac felt that a 350 2-barrel with its 265 hp needed a beefier transmission if the car was equipped with A/C though.

What he noted is also what is shown in the Technical Information/Drivetrain ID section under 1969.