The three common ratios were based on the fact the rigs only had automatics, and zero overdrive's. My '79 GT came with a whopping 2.47 ratio. I have plans to swap in an AOD, so I have a Bronco 3.50 R&P to swap into the pumpkin when that happens.
That some great info. My goal is to put something together to get the best possible mileage on the road. Mine has a 351, and right now I’m getting a solid 17.7 mpg running about 63 mph. I’m hoping that with some tuning, a tonneau cover and possibly adding overdrive I can get it over 25.
Overdrive only works within a narrow band on engines. You have to keep the engine within about 1800-2200 RPM at sixty MPH to get the highest possible MPG, but remember...a brick only flies with enough power behind it. At that 17.7 MPG/63 MPH, what is your 351 V8 turning at? Another thing to consider: Cruise-o-Matic transmissions do not have a 'lock-up' converter. There's a bit of slippage in the torque converters of those earlier transmissions, and was not addressed until the Automatic Overdrive design that put a torque converter clutch inside, which, when engaged, gives you a 1:1 coupling, hopefully with no slippage. Look at the Panther cars of 1979 and up, the LTD/Crown Vic, Grand Marquis and Mark VI/Town Car, and see what they do to get 20+ MPG from a 302 or 351W, carbed vs. fuel injected, etc.
Okay. I should ask, does your cluster have a tach, and if not, would you have something, like a Sears engine analyzer, that could sub in, give engine RPM's?
Interesting, as my '74 Squire with the 351C had the 2.73 ratio. I wonder if that was because the 351W was an IMCO engine, whereas the 351C was not continuing past '74, so it was not given the IMCO treatment.
That's mostly true, but the AOD doesn't have a lockup clutch. It has a unique shaft that connects the torque converter housing to the direct clutch so that when the direct clutch applies (in 3rd & 4th) the crank is connected directly to the planetary gears eliminating the torque converter. That means no possible slippage. Giving, as you correctly stated, 1:1 coupling thru the converter. It's a neat system in that it doesn't wear out (like a clutch) and it doesn't let the converter try to multiply the torque in overdrive (which creates a lot of unnecessary heat). If you drive a car with an AOD you can feel this when the 2-3 shift happens, there is a funny bump because there is no longer a cushion provided by the fluid drive. Like I said, it's unique to the AOD. I don't know of any other manufacturer that did this. There are no electronics or computer involved, and it won't wear out. This is only on the AOD. The AOD-E and 4R70W both have the typical lockup clutch in the converter.
That's interesting, I'll have to look that up again, because my understanding is that the T/C does have a clutch, and the shaft hydromechanically locks the converter, whereas the electronic units only use hydraulics controlled by a solenoid. But I will do a bit of research. Who knows, maybe we're both right?
