flexplate question
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I'm not sure about your question the way you phrased it, but I think you are asking what the maximum engine output torque that can be input into the torque converter (directly bolted to the flexplate) of a stock 4R100, as opposed to what the maximum input shaft torque is to the 4R100 transmission gearbox itself after the engine torque is multiplied by the torque converter.
Is this along the lines of what you are asking?
I think we can assume that Ford limited the 7.3L's torque on the automatic to 505 ft lbs (versus 525 ft lbs with the manual) to stay within, but probably very close to the maximum of the stock 4R100's engine input torque rating.
We might be able to confirm this by considering the stall torque ratio of the torque converter. Stall torque ratios (STR) are generally between 1.7:1 to 2.1:1. I have read, more than once, but don't quite remember where, that the STR of the stock 4R100 converter is 1.9:1.
If we take the 7.3L 505 ft lb torque rating for automatics, and multiply it by 1.9, we arrive at 960 ft lbs of multiplied torque acting on the transmission input shaft.
The "100" in the 4R100 designates a 1,000 ft lb input torque rating, and 960 ft lbs is close to that.
The manual transmission 7.3L were rated at 525 ft lbs engine torque. Let's supposed that an automatic destined 7.3L was let out of the barn with this rating. 525 ft lbs multiplied by an STR of 1.9:1 is 998 ft lbs, or just barely under the 1,000 ft lb input shaft rating.
So it seems reasonable to assume that the absolute maximum engine output torque applied to the torque converter (bolted to the flexplate) that is acceptable for a stock 4R100 converter and tranny is somewhere below 525 ft lbs, while Ford limited the calibration in the automatics to a slightly more conservative 505 ft lbs.
Is this along the lines of what you are asking?
I think we can assume that Ford limited the 7.3L's torque on the automatic to 505 ft lbs (versus 525 ft lbs with the manual) to stay within, but probably very close to the maximum of the stock 4R100's engine input torque rating.
We might be able to confirm this by considering the stall torque ratio of the torque converter. Stall torque ratios (STR) are generally between 1.7:1 to 2.1:1. I have read, more than once, but don't quite remember where, that the STR of the stock 4R100 converter is 1.9:1.
If we take the 7.3L 505 ft lb torque rating for automatics, and multiply it by 1.9, we arrive at 960 ft lbs of multiplied torque acting on the transmission input shaft.
The "100" in the 4R100 designates a 1,000 ft lb input torque rating, and 960 ft lbs is close to that.
The manual transmission 7.3L were rated at 525 ft lbs engine torque. Let's supposed that an automatic destined 7.3L was let out of the barn with this rating. 525 ft lbs multiplied by an STR of 1.9:1 is 998 ft lbs, or just barely under the 1,000 ft lb input shaft rating.
So it seems reasonable to assume that the absolute maximum engine output torque applied to the torque converter (bolted to the flexplate) that is acceptable for a stock 4R100 converter and tranny is somewhere below 525 ft lbs, while Ford limited the calibration in the automatics to a slightly more conservative 505 ft lbs.
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