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RE: Engine Math...a little

Posted by JURB (A) on April 21, 2021 at 14:45:42

In Reply to: RE: Engine Math...a little posted by grantv on April 20, 2021 at 07:00:22:

"Turbo Hydramatic 3 speed auto. A heavier duty unit was the Turbo 400, usually only in big block cars IIRC"

I think you mean the Hydramatic. They were a heavy ass bitch. When they got to the THM400 they had much more going for them. Lighter for one, and the bigger gearset made possible a lower low gear.

With the new torque convertor they had some minor control over stall speed, so these things would take off at 5:1. If not for that convertor you would need a truck transmission to do it and that definitely means bucket seats, small ones. The actual gear ratio is like 2.6:1.

I had one apart a few times, the valve body is a veritable analog computer. The book showed where convertor pressure went, governor pressure, vacuum modulator pressure. These all go to valves with multiple pistons that calculate when to shift - better than you can because it had engine parameters at the time than you do. These multiple pistons act like gates in a computer. Get to a certain point it is time to shift.

they also had electric passing gear, good to 70MPH they said, but in my Toronado the THM425 which is the same thing but folded for front wheel drive had a passing gear at 105MPH. I didn't take it much farther, I needed a tire and it took LR78s, the highest rating I could find on town was a JR78. not to mention it was on the front. But the one I worked on was a later one, my road ripper was a 1970, this was IIRC a 1976.

But remember I had the book on it. This book, damn, had a diagram of the valve body just like a schematic and had actual overlays, printed on clear plastic that you put on the main drawing to see what just happen when...whatever. I wonder if they even print books like that anymore.

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