Thread: 20+mpg small block with carb.

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MikeP,

Thanks for your reply. There is a page with a lot of good information on the 700R4 at the PATC site.

700 Raptor 700R4 700R4 Transmission 700r4 700R4 700r4 PATC 700R4 700r4 700r4 700r4 700r4 700r4 700r4 700r4 700r4

It mentions that the STALL rpm depends on weight of car and engine power and a BBC may have a stall rpm as much as 700 rpm higher than the same converter with a SBC. It also mentions that 1985 and up 700R4 trans will shift OK without the electrical connection but 1984 and earlier need the electrical switch to achieve lockup. I purchased my 700R4 from PATC because I wanted their conversion to a hydraulically controlled OD lockup so that is why I am trying to figure out at what (pressure) rpm the lockup releases. In principle the electrical lockup is controlled by the switch not the rpm. So now I understand that it is the downshift rpm that is important with the hydraulic lockup. The PATC site mentioned above does say that the rpm should be at least 2000 at 70 mph so my formula given above can be used to see if a given rear ratio and tire size can meet that condition. Ideally I would like to shift into OD at about 50-55 mph and so far my rear and tires seem to be in that range. Well I have learned about the OD lockup but I guess I will just have to wait and see where my 3rd-to-OD shift point turns out to be.

Don Shillady
Retired Scientist/Teen Rodder