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Looking for opinion on 3.55 gears in a 68 GTO with a four speed manual. Is that going to be a good all around gear for a daily driver? I understand the 3.55 gears were the norm for cars with the four speed, but of course 50 years ago, gas was cheap. I would like to have lower rpms at highway speed, less heat, less noise, better gas mileage. Are the 3.55 gears going to be a decent ratio?? Thanks in advance for your input!
 

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Looking for opinion on 3.55 gears in a 68 GTO with a four speed manual. Is that going to be a good all around gear for a daily driver? I understand the 3.55 gears were the norm for cars with the four speed, but of course 50 years ago, gas was cheap. I would like to have lower rpms at highway speed, less heat, less noise, better gas mileage. Are the 3.55 gears going to be a decent ratio?? Thanks in advance for your input!
I have the Muncie 4 speed and 3.55 rear in my 65. I think the rear is fine for around town, but if you are planning on a lot of highway driving, you may want to consider a taller gear IMHO.
 

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Looking for opinion on 3.55 gears in a 68 GTO with a four speed manual. Is that going to be a good all around gear for a daily driver? I understand the 3.55 gears were the norm for cars with the four speed, but of course 50 years ago, gas was cheap. I would like to have lower rpms at highway speed, less heat, less noise, better gas mileage. Are the 3.55 gears going to be a decent ratio?? Thanks in advance for your input!
What type transmission? M20, M21 M22?

If you use one of the online calculators you can determine your engine's RPM at whatever speeds you want to run.

The 3.55's were a good gear when the national speed limits were 55MPH. Not so good if you plan on running 70MPH.

As you drop below 3.55's you want to take into consideration that it may use a little more clutch technique in slipping the clutch to get rolling. 3.23's are about as low as you really want to go, but you can run a 3.08 with the low first gear.

The only real way to have your cake and eat it to is to use an overdrive transmission.
 

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Discussion Starter #4
What type transmission? M20, M21 M22?

If you use one of the online calculators you can determine your engine's RPM at whatever speeds you want to run.

The 3.55's were a good gear when the national speed limits were 55MPH. Not so good if you plan on running 70MPH.

As you drop below 3.55's you want to take into consideration that it may use a little more clutch technique in slipping the clutch to get rolling. 3.23's are about as low as you really want to go, but you can run a 3.08 with the low first gear.

The only real way to have your cake and eat it to is to use an overdrive transmission.
Thanks PontiacJim! The info you sent in regard to my other post seems to be answer to what I am looking for!
 

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Thank you Bear. I am looking for a car comfortable to drive anywhere.....no interest in burning up $200 tires, etc. Maybe I should be considering a non-four speed....
 

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Thank you Bear. I am looking for a car comfortable to drive anywhere.....no interest in burning up $200 tires, etc. Maybe I should be considering a non-four speed....
Hmmm, maybe you should consider a new Cadillac....Just saying.....
 

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I ran 3.55 gears in my 4 speed '67 GTO. I thought it was a great gear, but couldn't leave it alone. I went to 3.73 gears. Big mistake. Engine worked harder. More gas. Tough on the interstates which I tried to avoid. I'm presently running 3.55 gears in my '71 GTO with a TH400 trans. They work very well for my driving habits. I wouldn't want any gear numerically higher without an OD transmission. That's just me.
 

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I also have 3.55 with a four speed, it's perfect for me. It has impressive acceleration , but runs about 2500 rpms at 55-60 mph. I wouldn't want to go with a Lower rear gear, as it is you can't be driving it down the highway without high rpms.
 

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I am a little surprised by the conservative gear ratios that seem popular in this thread. I am installing a Quick Performance rear axle assembly in my wife's 65 421 Tripower GTO 4 speed manual car.
It had a 3.3x r&p in the 8.2 open diff stock rear axle. I have selected a 3.80 ring and pinion gearset and TrueTrack posi for the 9" Ford based upgraded rear axle assembly. With 8"x17" front and 9"x17" rear aluminum Rally 2 wheels and the current 275/40/17 Toyo Proxes TQ drag radials on the rear, the 421 will be turning about 3,500 RPMs in 4th at 70. Now I understand that may sound like a lot, but my 70 440 6bbl Roadrunner with 3.55 gears and 315/35/17s turned about the same RPMs at 70.
In my Roadrunner I now have 4.10s in my Dana 60 because I switched out the 4 speed to a Passon 5 speed w/a .70 overdrive 5th gear. 70 mph is 2,750 now. Our highway drives are typically 1 hour or less, and if we decide to do the Power Tour or some other long distance cruise I can swap in a lower numerical highway friendly chunk in the 9" housing fairly easily without too much expense. The other possibility is my wife may be ok with a more modern 5 speed manual transmission swap in the future. Even if we keep the 3.80 and 4 speed Muncie, for the way we drive, with lots and lots of 35-45 mph speeds cruising, I believe the much improved "pep" the 3.80 will provide is going to be better appreciated than tall highway gears. She also has a 1/4 mile goal of mid 12s, so the 3.80 is going to be better for that too. The 421 has some substantial go fast+last longer parts in it from a rebuild and the rev limiter is set for around 5,900 RPMs. It has a top speed of appx 118 mph at redline, so it will make the 1/4 mile without hitting the rev limiter in 4th.
 

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I am a little surprised by the conservative gear ratios that seem popular in this thread. I am installing a Quick Performance rear axle assembly in my wife's 65 421 Tripower GTO 4 speed manual car.
It had a 3.3x r&p in the 8.2 open diff stock rear axle. I have selected a 3.80 ring and pinion gearset and TrueTrack posi for the 9" Ford based upgraded rear axle assembly. With 8"x17" front and 9"x17" rear aluminum Rally 2 wheels and the current 275/40/17 Toyo Proxes TQ drag radials on the rear, the 421 will be turning about 3,500 RPMs in 4th at 70. Now I understand that may sound like a lot, but my 70 440 6bbl Roadrunner with 3.55 gears and 315/35/17s turned about the same RPMs at 70.
In my Roadrunner I now have 4.10s in my Dana 60 because I switched out the 4 speed to a Passon 5 speed w/a .70 overdrive 5th gear. 70 mph is 2,750 now. Our highway drives are typically 1 hour or less, and if we decide to do the Power Tour or some other long distance cruise I can swap in a lower numerical highway friendly chunk in the 9" housing fairly easily without too much expense. The other possibility is my wife may be ok with a more modern 5 speed manual transmission swap in the future. Even if we keep the 3.80 and 4 speed Muncie, for the way we drive, with lots and lots of 35-45 mph speeds cruising, I believe the much improved "pep" the 3.80 will provide is going to be better appreciated than tall highway gears. She also has a 1/4 mile goal of mid 12s, so the 3.80 is going to be better for that too. The 421 has some substantial go fast+last longer parts in it from a rebuild and the rev limiter is set for around 5,900 RPMs. It has a top speed of appx 118 mph at redline, so it will make the 1/4 mile without hitting the rev limiter in 4th.
Did you read the original post? "I would like to have lower rpms at highway speed, less heat, less noise, better gas mileage."

3.89 (Ford) or 3.90 (Pontiac) will definitely not fit the goal of the original statement. Running an engine at 70 MPH @ 3,500 RPM's in my book is not the best if you plan on taking your car to a show 1hour or more away from home. Some of the shows I frequent are 4 hours away and I would not be comfortable running my engine at 3,500 RPM's for 4 hours and back - and I don't "trailer queen" my cars and never will, why own it?

If all I did was local around town, stop light to stop light driving, I might be OK with a set of 3.90's, but gas mileage would be right down the tubes. Had one with 3.90's and got about 10 mpg's and was why I pulled it and put in 3.08's at the time. The higher RPM's also speeds up wear & tear.

"but my 70 440 6bbl Roadrunner with 3.55 gears and 315/35/17s turned about the same RPMs at 70." Tire height can change the RPM's, so a taller tire with 3.89's can be the equivalent of 3.55's with a shorter tire. Just another way to adjust your RPM range.

The advantage of a 9" is that you can swap "meatballs" to change the ratio, but not going to happen with a 10 or 12 bolt. Interesting that you installed a 5 speed to take advantage of the 5th gear OD for cruising and lowered the RPM's. Why? I think you should have followed with the 421 gearing to keep the RPM's up, something like 4.88's or 5.13's? So kind of a mixed message you are sending. :confused
 

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...but my 70 440 6bbl Roadrunner with 3.55 gears and 315/35/17s turned about the same RPMs at 70...
Respectfully, so what? That 440 of yours has a 4.32 bore and a 3.75 stroke - (same stroke as a Pontiac 400). That 440 also has a "tiny" 2.270 main journal size. According to what I see on the net, peak torque was in the neighborhood of 480 lb ft at about 3200 RPM.

Now, Pontiac 421: Bore 4.093, stroke 4.00, main journal size 3.250. Right out of the box this engine has a .25" longer stroke and a .50 larger main journal than that 440. That longer stroke alone means it's going to make torque lower in the rpm range than that 440 does. Depending on whose specs you use, it made about 460 lb ft at 2800 rpm. That was peak. If you look at the whole torque curve you'll see that from zero to 2800, that 421 Pontiac is making a lot more torque than that 440 at every point on the chart. (By comparison, my 461 Pontiac stroker with 4.155 bore, 4.250 stroke, 3.00 mains makes about 560 lb ft by 3100 rpm)

So why do we run these gear ratios in our Pontiacs? Because they're the right ratios to keep these engines in the RPM range where they make the most torque, that's why. And the larger (and much stronger) mains on the 421 do make it a little more difficult to oil, but since there's no reason to rev these engines to the moon to get the most out of them, we don't.

Chevy guys are always worried about making changes that will hurt their bottom end torque. We don't have that problem. Our problems tend to be too much of it, so that getting the cars to hook is difficult. 0:):grin2:

Bear
 

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Late to the party here: I had 3.55's in my 4-speed '65 for years. When I had the rear end rebuilt, I changed to the lowest numerical gear my carrier would support, a 3.36. Not much of a difference on paper, but a huge difference on the road. My 60 MPH cruise went to 70 mph. Later, I added taller (29") rear tires, and now effectively have a 3.23 rear gear ratio....which is perfect for in-town and on the open road with a stock 4 speed and the 389 Tripower in my car. I like cruising at under 3000 rpm. I can hear the radio, the car uses less gas, and it runs cooler, as well.
 

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Looking for opinion on 3.55 gears in a 68 GTO with a four speed manual. Is that going to be a good all around gear for a daily driver? I understand the 3.55 gears were the norm for cars with the four speed, but of course 50 years ago, gas was cheap. I would like to have lower rpms at highway speed, less heat, less noise, better gas mileage. Are the 3.55 gears going to be a decent ratio?? Thanks in advance for your input!
8

I have 3.55 gears with 4 speed in my vette, depending on your tire height, it stinks on the hiway. At 70 your somewhere around 3400 rpm if I remember correctly
 
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