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290 to t-4 or 904 questions

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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Apr/09/2021 at 6:09am
You've actually got a Borg Warner M-40, which is a bit stronger than a 35. Keeping the stock 69 six there really isn't much you can do as far as a stronger transmission -- nothing else bolts to that motor. Later AMC sixes are pretty easy to get though, so it would be better to get a builder 1972 or later 258 (or even a 4.0L, even if you put a carb on it) and use the Chrysler 904 or 998 trans. You can use the same trans behind a 290 or any other 67-71 AMC V-8 by buying an adapter for the earlier engine. The six cylinder 904 is a little weak for a built-up 290/304, but would be fine for a cruiser as long as you install a towing/HD shift kit, and I'd install an external cooler as well. The 304 typically used a 998 trans, which is a bit stronger than a 904. 360 and larger used the 727, which is overkill, really. A 727 is a great trans, but it's very heavy and takes a lot of power just to turn. Most drag racers use a built 904 or 998, but that cost a good bit to rebuild with the upgraded parts to handle a lot of power. A mild 290 (small 4V and cam) will be fine with a 904/shift kit/added cooler for cruising around and an occasional fun pass down the strip, but if you plan on running it hard a lot go find a 998 (Eagles and Jeeps used a 998 or later model CJs 999), but they are all 4x4. IIRC the output shaft and housing from a 904 will fit a 998/999, but trans must be torn apart to change. You could also go with a AW4 four speed auto from a 2WD Cherokee. There is a thread in the trans section about using one of those. Nice HD trans with overdrive, and bolts right up with the late to early trans adapter. You could also use an adapter from Novak or Advance Adapters for a GM 200R4 or TH350.
Frank Swygert
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