[changzuki]

Originally Posted by GreenHornet

Something most people do not know about the overdrive units on these Spitfires. Most people are only aware of the A type having a .82 or (22%) taller ratio but they also had the .78

J type = .8 (25%)

A type = .78 (28%)

So I am just curious as to why you did not go this route? The J type are much more abundant over here in North America as they were fitted to all of the Spit 1500 cars with overdrive. You can also find them on Volvo transmissions which came standard I believe. These .78 A types you probably would have to find over in Europe. So more work but possibly better efficiency as well. Food for thought if nothing else something to look into if you ever get the Centurion optimization bug again down the road.

GH

Welcome back GreenHornet,
Considerations for using the J-Type overdrive came down to:
- Parts availability & Price -
Price was a big factor especially since I figured the D850 wouldn't be able to effectively drive the car in overdrive unless it was on some type of downhill. If this setup was going to fail, debt load needed to be low.
- Reviews -
There's plenty of internet discussions about the overdrives used in Spitfires. I probably read every one of them - twice. A major influence came by way of John Esposito (Quantum Mechanics). It may be hard to find a single source with so much experience in both repair and testing than him.
- The Legend -
Initially, a 5 speed conversion is what I wanted, but, wish in one hand and....
Even more tantalizing was the idea to mimic RQ Riley's original plan using the Spitfire option - with the modern twist of the 3.27 differential instead of the factory issue 4.11
It would be a great comparison to the original Centurion without deviating too much from the original plans. With any luck I can get some hard numbers to publish this summer, and, if for any reason the setup fails - at least another scenario would be covered.
Not sure I could ever bring myself to do it, but IF (as you suggest) the "optimization bug" ever hit this Centurion again - it would be completely spent in the aero department and the end result would likely not even resemble a Centurion... There would be no reversal... A period classic would be lost....
~CrazyJerry
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