1800: Lowering RPM on 1800E with automatic transmission

[142 Guy]

Just about anything is doable; however

Whilst changing to an AW70/71 would not be difficult in the OP's P1800

the 'not be difficult' part - maybe not so much.

The AW 70/71 were fitted to the tipped over, over head cam redblock engines. Even if the bolt holes and mounting circle for a B20 bell housing matched up with the tipped over AW 70/71 bell housing, you would still be into sectioning the bell housing, rotating the mounting flange and welding it back together to get the transmission to sit with its correct orientation. If the bolt circle / mounting holes do not match up then you are faced with fabricating an adapter flange, sectioning the bell housing and welding on the adapter flange in the correct orientation. You then still have the question of the attachment of the transmission to the engine.

Its probably doable. Its not going to be a primarily exchange parts and bolt in like most M41 conversions so the 'not be difficult' will depend on your fabrication and design skills or willing to set up a printing press to produce money to have a fabricator do it for you . The AW 70/71 OD ratio of 0.69:1 and a 3.9:1 final drive would make for much more relaxed highway cruising. But, the slightest headwind or hill will force a downshift because US spec B20F engines are not exactly power houses.

It might be easier to transplant the AW 70/71 with the B230 attached rather than try and graft it on to the B20. I have seen an Amazon with a B230FT installed in it so it is probably doable in the 1800. An 1800ES with an AW 71 and a B230 FT would not suffer from headwind problems.

With a 3.9: 1 rear end and the BW 35 transmission, the reported 3000 RPM at 90 km/hr would seem to be correct. If the noise is excessive, I might be first inclined to investigate some noise abatement before embarking on the transmission changeout exercise.