Help calculating RPM

Baker7888

Master Mechanic
Dec 3, 2021
392
28
Maine
Hey guys was hoping someone could help me calculate RPM based on speed for my setup which is a close ratio T-10 4 speed (cast iron 63 vette) with a 4.10 rear and a 26.5” tire

I am looking for what RPM i will be running at 70 mph in 4th gear. I have this setup now (speedometer incorrect) and regret my decision on gears. Thinking of going to a 3.23.
 

Baker7888

Master Mechanic
Thread starter
Dec 3, 2021
392
28
Maine
Spoke too soon i guess. Looks like spicer has a calculator. I think 4th on a t-10 is 1-1?
If thats the case then with a

4.10 at 3000 rpm equals 58 mph
3.23 at 3000 rpm equals 73 mph

Does this look correct?
 

scoti

Royal Smart Person
Supporting Member
Sep 5, 2019
1,691
113
Texas
Spoke too soon i guess. Looks like spicer has a calculator. I think 4th on a t-10 is 1-1?
If thats the case then with a

4.10 at 3000 rpm equals 58 mph
3.23 at 3000 rpm equals 73 mph

Does this look correct?
Yes. Looks correct.
 
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Reactions: 1 user

Streetbu

Know it all, that doesn't
May 22, 2011
3,454
113
Central NY
You'll hate 4.10's for anything other than 0-60 full throttle runs, and 30mph cruising. Unless you had overdrive which you don't. I wouldn't go any higher numerically than 3.42, 3.23 would be a decent choice too.
 
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Reactions: 2 users

Baker7888

Master Mechanic
Thread starter
Dec 3, 2021
392
28
Maine
You'll hate 4.10's for anything other than 0-60 full throttle runs, and 30mph cruising. Unless you had overdrive which you don't. I wouldn't go any higher numerically than 3.42, 3.23 would be a decent choice too.
Ya i ordered 3.23. Didnt think the 4.10 would be as bad for some reason
 

Baker7888

Master Mechanic
Thread starter
Dec 3, 2021
392
28
Maine
Taller tires would take some rpm out of the total but not by much.
Good idea. I have a pair of 295/50/16 at about 28.5" tall but they are too wide And will scrub the frame
 

565bbchevy

Geezer
Aug 8, 2011
9,275
113
Michigan

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