Can someone tell me if the factory Powerglide transmission used with a 1970 230 or 250 engine was EXACTLY the same as the Powerglide transmission used with a 307 engine? I have a 1966 Chevelle assembly manual that shows the Powerglide as apparently being the same for a 230 or 283 engine, but I don't know what the situation was with later small blocks. I don't remember what the ratio was in the 1966 instance, but I think the 230 and 283 used a 1.82 ratio, while the 327 and larger V-8 engines used a 1.72 ratio.

Thanks for the help. Essentially, I want to know if I can buy a Powerglide from a 6-cyl engine and put it behind a 307 -- and have it be exactly the same as the transmission that would have come with the 307.

If you really want "absolutely exact", no, they are different in minor ways, but alike enough that you can swap them with no grief. You wouldn't even notice the difference in gear ratios if they were different.

Your assumptions are correct, and what Jon said is correct. The 307 Powerglide is really the same as a six cylinder Powerglide (especially the 250 version). The 250 version is liquid cooled and the same as a 307 version, only the shift points might vary slightly. A friend's brother had a '67 Malibu with a 230 Powerglide (air cooled PG no less). The first winter he had it he swapped in a nearly new 307 (this was back in '75) and kept the Powerglide. He added headers, intake & 4-barrel. There was never a problem during the remaining 3 years he owned the car, and he would kick it down on the highway and let it fly. A 307 isn't going to kill it.

Perhaps someone can clarify something mentioned in one of the replies -- the suggestion that perhaps only the 250 used a liquid-cooled transmission. My '66 Malibu left the factory with a 230 and liquid-cooled Powerglide, and the '66 Chevy chassis service manual confirms that the air-cooled Powerglide was an option for the 230 in 1966. I think the air-cooled Powerglides were probably gone in 1968, but I don't know for sure.

I know the 307 would not have used an air-cooled transmission, so I would only use a fluid-cooled tranny with the 307. I imagine that in '69 or '70, a fluid-cooled Powerglide used in a 230 or 250 is exactly the same, so putting either with a '70 307 would be o.k. if the 307 used a similarly geared tranny. If shift points were different among the different engines, I imagine the shift points could be changed during an overhaul.

If anyone has a '70 Chevy chassis service manual, can you look in the back to verify whether the 230, 250, and 307 engines used Powerglides having the same ratio (1.76 or 1.82 were the two choices, I think).

Thanks again.

All I can tell you is that in 1965 all powerglide transmissions bolted to a 6 cyl. were air cooled (no cooling lines). Powerglide transmissions bolted to an 8 cyl. had cooling lines going to the radiator. I believe the internals of the transmissions were the same.
I don't think you could put an 8 cyl. powerglide in a 6 cyl. car (unless you changed the radiator to accept cooling lines).