I am faced with what some would say is a simple choice as I have 0.73 OD T5 and a 1955 Axle with 3.90 Gears. Why wouldn't I switch from my SM420 with 3.55 rear end?
On my drive wheels I will be running 235/85 R16s
I wanted to see the RPMs across MPH for these two options - The spreadsheet I cooked up plots this ... Solid lines are the t5 driveline option and the dash lines are the SM420
[img]
https://photos.app.goo.gl/3qKfS6HTVCJy8dCr5[/img]
A comparison of top gear for each driveline makes it clear that the T5 is hard to beat .. In this chart a negative number means the engine for the T5 is spinning that many Rpms slower.
[img]
https://photos.app.goo.gl/9yyt5SMLfg6NXeNk7[/img]
I am not looking for interstate cruiser but it would be nice if I could do 65 now and then. Keeping the SM420, with the tall tires, at 65 mph, the engine will be spinning just above 2500 rpms. At 70, it will be spinning at about 2800 rpms, which I have seen often as a nice cursing RPM. Thus, at the moment, I am not going to swap in a T5.... The Granny gear is great for parades and sentimental reasons as my school buses when I was a kid must have used SM420 -- brings back memories of a simpler time.
