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GTO Gear Ratio's

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geeteeohguy
Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer.

I've run GTOs over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTOs with stick shift usually came through with 3.55 gears, and auto cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accommodate gears from 4.88 or so down to 3.36. The 3 series carriers could accommodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time. The top end was ok. The low-end was great. Good "all around" gear, back then.

Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, unneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the highway. The top end was 107 mph, at the redline. It would get there really quick, though. I changed out those 3.90s with a 3.36 gear set (the tallest gear set I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down.

I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accelerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the highway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure.

Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph, in 4th gear. Scary. The cruising speed was 55 mph. Got about 8mpg at 55!

My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption.

Today, there are a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans or add a 5 or 6-speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs.

For this guy, it's 3.23s.

Jeff
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Rukee
Great post!
My `65 had 3.90s in it when I bought it, and for 13 yrs the car never left town cause the RPMs on the highway were just too high for my comfort level. It was fast, no argument there, and at 35mph I could smoke the tires twice within about 10 feet in a second. Once when I punched the throttle and the second when I snapped off the throttle it would bark the tires again as they slowed down.

Then a couple of years ago after my wife passed away I really wanted to drive the GTO to some other shows out of town, so I changed out the rear gear to the ratio it had from the factory, the 3.55s. I couldn't believe the difference! It goes down the road like a dream and actually feels faster as each gear seems to have longer legs.

I think Pontiac did a great job of picking the right ratios right from the factory and I wish I had changed the ratio back years before.
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blondie67
Gear Ratios

Hi,
thanks Jeff for the post...I know there were a lot of gear options for the 67 and whether it had the safettrack or not. At least in my book there seems to be many. Does the rear axle code stamped on the axle tube determine the gear ratio? And if changed out, would it still be there? Ok I know that sounds like a dumb question, but I want to go check on it today.
Linda
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E
My 67 has 2.93 gears....doggy off the line great top end..by todays standards it still feels like it needs another gear (TH400)....I was thinking of a set of 3.73 with a 4spd auto..200r4 can be built to take some torque. It is also an easy swap ....shorter yoke on the drive shaft..and a kit to adapt the his/hers.............Cool Thread
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geeteeohguy
Thanks, folks. Yeah, we've become spoiled with lock-up converters and overdrives. The 200R4 and 700R4 seem to be the swap of choice, provided you run a fairly stock engine. My 3.36 '67 feels like it needs another gear out on the open road. But in the '60s, gas mileage wasn't a concern.

Linda, yes, the axle code is stamped on the rear end. On your car, it will be a two-letter stamp, on the right side axle tube, facing the rear. the codes begin with a W for standard, open diffs, and a Y for safety-trac (posi) units. Yours should be a WG or a YG for 3.36 if it's the standard ratio. They run WB/YB=2.56, WC/YC=2.78, WD/YD=2.93, WF/YF=3.23, WG/YG=3.36, WH/YH=3.55, WE/YE=3.08, and WK/YK for the 3.90 ratios.

The only way to tell if the gears were changed is to remove the rear cover and look at the numbers on the gears denoting the number of teeth, or counting the teeth on the ring and the pinion. I have those numbers also if you need them. I think in today's day and age, with the amount of torque and power a Poncho engine has, short gears like the 3.90, etc. are not needed for most drivers. Those gears are better left to high revving, low torque, hi horsepower small block engines.

Good luck with your hunt. To me, that's the fun of this hobby!

Jeff
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Try this site and input values:

ULTIMATE PONTIAC GTO PICTURE SITE Text Topics article #29
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Rukee
The ratio can also be pretty well estimated by jacking the car up and spinning the rear wheels over. Count the # of drive shaft revolutions needed to make the tire rotate 1 full turn. That`s for a posi rear end, if you have a 1 wheel wonder, only jack one tire off the ground and then spin that 1 wheel 2 full revolutions and count the # of drive shaft revolutions for the gear ratio. My drive shaft turns 3 and just over a half revolutions for every time the tires roll over once for a 3.55 ratio.
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LOWET
geeteeohguy said:
Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on: Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer. I've run GTO's over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTO's with stickshift usually came through with 3.55 gears, and aut0 cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accomodate gears from 4.88 or so down to 3.36. The 3 series carriers could accomodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time.Top end was ok. Low end was great. Good "all around" gear, back then. Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, uneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the hiway. Top end was 107 mph, at redline. It would get there really quick, though. I changed out those 3.90's with a 3.36 gearset (the tallest gearset I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down. I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accellerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the hiway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure. Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph., in 4th gear. Scary. cruising speed was 55 mph. Got about 8mpg at 55! My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption. Today, there's a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans, or add a 5 or 6 speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me, and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs. For this guy, it's 3.23's.
Jeff
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I had 513s in my 67 Camaro. I could get it to wheelie in 1st and 2nd
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VettenGoat
Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
Mike
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blondie67
The reason I asked....

The reason I asked this question is that the previous owner I think put 4.11 (is this right?)gears in it and it feels like it needs 2-3 more gears on the freeway. It's great around town, but I want to change it back to stock so I can cruise this summer.
Thanks for all your input!
Linda
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E
4.10 gears are too stiff for cruising....about 3000 rpm's to do 55. You will shorten your engine life and not enjoy the ride.....3.55 is probably a good ratio to use "Ask your Doctor if 4.10's are right for you".......if I never hear that commercial phrase again ......................:rolleyes:
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geeteeohguy
VettenGoat: In my opinion, especially with a 421, I would get a "year correct" rear end for your car and run a 3.23 gear or a 3.36 gear. A 3.55 gear with a 421 would sure be great around town, but you'll be wound out on the freeway, looking at shorter engine life, higher engine temps, more road noise, and less fuel economy. The 421 has enough torque to run a really long legged gear like a 2.93 or a 3.08 and still not be able to hook up! I would suggest going for a ride or driving a 3.73 or 3.55 geared car and see how you like it. With me, it was great when I was 19, but now, I like to get in the car and GO SOMEWHERE!!! As for 5.13 gears, Yeah, I saw a guy in a white '67 Camaro one day waaay back when pull the front wheels up about 18 inches out af a stoplight on San Leandro Blvd. Needless to say, I didn't even race THAT Chevy!!!!
Jeff
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Rukee
The size of the engine won`t change the RPMs. I have 3.55`s with a 4-speed and it goes down the interstate with ease. I even raced a Bemmer looking thing up to about 125 and it was still pulling away strong. I drive the car all over the state and it cruzz`s awesome down the highway. A lower # ratio would get better millage, but who drives their classic GTO for gas millage?? :D
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geeteeohguy
You're right about the RPM's, Rukee. But a 421 rev's lower than a 389, and makes more power at lower RPM's. While a 3.55 is the standard gear for a 389 equipped stickshift 3400 pound GTO, the usual gearset for a big Pontiac with a 421 and stickshift seems to be 3.42 or 3.36. 3.55 was considered the best "all-around gear" in the GTO back then....... Like you, I had 3.90's out back until I went as long legged as I could: 3.36's. I have no regrets!!!!!!
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ppurfield001
Rukee said:
The size of the engine won`t change the RPMs. I have 3.55`s with a 4-speed and it goes down the interstate with ease. I even raced a Bemmer looking thing up to about 125 and it was still pulling away strong. I drive the car all over the state and it cruzz`s awesome down the highway. A lower # ratio would get better millage, but who drives their classic GTO for gas millage?? :D
Click to expand...
I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?
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Rukee
Your best guess to figure it out would be to do like I suggested above with a jack. You can get very close to what the real ratio is.
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05GTO
ppurfield001 said:
I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?
Click to expand...
Pull the diff cover and count the teeth on the ring and pinion, then divide the # of ring teeth by the number of pinion teeth.

Another way is by using Rukee's method and turn the tire 10 times and if the drive shaft turns 39 times the ratio would be a 3.90.
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Rukee
10 tire revolutions is too many, between counting the tire and the driveshaft it` too easy to lose count. :eek:
That`s what the ratio is though, how many times the driveshaft turns for evey one complete turn of the tires.
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ppurfield001
Rukee said:
10 tire revolutions is too many, between counting the tire and the driveshaft it` too easy to lose count. :eek:
That`s what the ratio is though, how many times the driveshaft turns for evey one complete turn of the tires.
Click to expand...
Thank you Rukee and Randy.
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LOWET
VettenGoat said:
Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
Mike
Click to expand...
The 3:55s should work well with a 421. they made a lot of torque
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