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Anyone decipher these numbers for gear ratio?

spinshop

spinshop

Veteran Member
Senior Member
I put new axles in my car a bunch of years ago and I took some pics of the gear to get the numbers but, I never check to see what ratio they were.
I had a guy check it by rotating the wheel but, I don't think they are 3:71`s. This thing screams when I get on the highway.
Going 60 the tack is 3K RPM`s.
Not sure if they are readable but, it`s all I got.
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spinshop said:
I put new axles in my car a bunch of years ago and I took some pics of the gear to get the numbers but, I never check to see what ratio they were.
I had a guy check it by rotating the wheel but, I don't think they are 3:71`s. This thing screams when I get on the highway.
Going 60 the tack is 3K RPM`s.
Not sure if they are readable but, it`s all I got.
View attachment 23156View attachment 23155
Click to expand...
Turn a wheel 1 rotation and count DS rotations, 3 3/4 turns is prob 3.73:1since my car has 3.73 and with either 27” or 28” tall tires WO OD I was at or above 3K rpm’s at 60 mph
 
Shovelrick said:
Turn a wheel 1 rotation and count DS rotations, 3 3/4 turns is prob 3.73:1since my car has 3.73 and with either 27” or 28” tall tires WO OD I was at or above 3K rpm’s at 60 mph
Click to expand...
That’s what the guy did but, someone I was talking to today thought it was kind of high RPM’s for 3:73.
Ok, my next question is, what gear is good for highway driving?
Not that I drive a lot on the highway but, sometimes I do.
 
spinshop said:
My tires are 26” so, I guess it makes sense. I don’t really like it. It’s like I need to shift.
Click to expand...
Depending on 10 or 12 bolt Id go with 3.07-3.08 to 3.23, I think stock rear gear on the 70-72 SS was around 3.23 for a BBC with an auto 3 spd trans and back then a 75 mph highway speed limit, I drove my 58 Apache with a warmed up 66 327, factory 4 spd auto and 66 12 bolt posi with 4.56 gears from St Pete to Orlando round trip about 90 mph, that little SBC was Screaming But didnt miss a beat 👍👍😁
 
This little truck our Furry kids dr built has a 66 283 & 2 speed powerglide with 3.23 rear gear and doc says it cruises nice on the highway and around town, didn’t think to ask him what tire size when I was there today
 

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I forgot about 2.73 they were a pretty standard rear gear too, not to great off the line unless you had a lot of torque, in the late 80's a friend built a 496 with 871 Weiand blower, 2-750 Holleys, nitrous that he put in his 70 Camaro with an M22 and 2.73 posi he like cruising on the hwy at very high speeds and the car had no problems burning out into 4th gear
 
As others stated, its not just gear ratio. Its the combined gear ratio, tire size, transmission ratio's, and converter (if automatic) and drive train power loss.

Drivability or "what's the best ratio" depends on the HP/TQ of the engine, min/max RPM the engine is built for, driving style (in town / country roads / highway) etc.

Yes a highway gear of 2.73 is amazing if you have 4/5/6 speed trans and driving on the HWY.

ORRRRR, in some cases, you have 500+ hp and your power to weight ration can cover the high gear. e.g. a 2.73 rear gear would be fine in a 3spd trans car driving around with 700hp. Not so good if the same car had 250hp.

I'm around 600hp with a TH350 (3spd trans) with 3.00 rear gear, 29" tall tire. My engine is built to go about 6200 rpm max. We drive on the interstate constantly so I wanted something that would keep up in traffic. Below is my data.

Im good with 3000 RPM at 78 MPH.

Now that might change here in the future and I may step up to 3.23 rear gear as I have a gear vendors sitting on the shelf that will add a 4th gear at .78. Putting my HWY cruise 2600 RPM at 80 MPH.

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I drove my '67 Chevelle SS L78 with 4-speed (M-20) and 4.10 posi from Illinois to Florida and back for Spring break 1968 (LOL!...good times! no worries, no Draft for me yet!) and I can't remember the RPM's on my Sun Tach but it should calculate up there (say between 2500 & 3,000 RPM?). Maybe someone can check. I had stock 14" bias ply tires on it then. It drove SWEET btw....drove straight through to Sarasota, then to Daytona Beach (drove it on the beach), then back to Illinois. My High School friend who went down with me (Rodney...RIP)...a Marine after that trip....couldn't drive stick so I drove the entire way down, but we picked up a couple friends from H.S. at Daytona and all 4 of us went back North together in my car....I fell asleep in the back seat and didn't find out until way later in life that they all had fun driving my car while I slept! LOL! Check me out re the RPM's though....I'd like to know! Btw, my engine with large dia. equal length tubing into long rectangular collectors (M/T SS Headers) likely put the horsepower well above 450HP which was huge for a stock engine back then.
 
ALL BEFORE MY TIME;
Coming in to Florida would have been old US1 (Dixie HWY) and or SR-4, and A1A beachside, as this was pre- I-95. Speed limit back then was 65mph i believe. I was born after (1973 in South Miami) and the Speed limit was the lower 55mph.

Stock tire sizes for that would be a 7.75x14 Bias tire (195/85/14 if you put it in todays sizes) 7.75" wide and 27" tall. Though you can still get the original design from Coker Tire.

M-20 trans gearing (2.52, 1.88, 1.47, 1.00) , 27" rear tire, 4.10 gear:
1727187380471.png
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So cruising at 2500-3000rpm would have been 47 to 56 mph. Driving the 65mph speed limit would have been 3500rpm.
 
Your friends probably had her buzzing around 4,000-5,000 rpm’s , in 78 me and a friend drove my 73 340 4 spd Duster with a built 340, I don’t remember what rear gear was in that car but it wasn’t stock, I woke up to my friend steering with his knees rolling a joint at 115 mph my eyes about popped out of my head when I looked at the speedo, engine sounded like a sewing machine wide open, Great GMA was a seamstress so I heard a lot of sewing machine lol, I zinged my 66 327 in a 58 Apache round trip St Pete to Orlando in 79 and I’m surprised those engines held together
 
My ‘67 L78 Chevelle took me round trip from Illinois to Florida & back, complete with stock size F70-14 tires Muncie M-20 4-speed and 4.10 posi. I don’t remember but I had a 10,000rpm Sun Super Tach and that baby was really humming along! I drove it 21 hours straight! Oh to be young again! 🥴
 
L78fanatic said:
My ‘67 L78 Chevelle took me round trip from Illinois to Florida & back, complete with stock size F70-14 tires Muncie M-20 4-speed and 4.10 posi. I don’t remember but I had a 10,000rpm Sun Super Tach and that baby was really humming along! I drove it 21 hours straight! Oh to be young again! 🥴
Click to expand...
I wonder what the cruising range of a full tank was ? Maybe 150 miles ? :)
 
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