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Old 10-25-2020, 07:57 PM
Formulas Formulas is offline
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In 1980-82 I ran 3.55 th400 400cuin. In my 1968 gto with a camshaft similar to the summit 2802

It needed the 3.55 in fact I cant stand a 3.08 and 400cuin combo even with a stock engine just to weak down low

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  #22  
Old 10-25-2020, 08:35 PM
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Stock 62 Tempest 195 cubic inch slant 4, 27 inch tire, Tempest Torque transaxle (think powerglide) 3:55 gears. 3300RPM at 70MPH. Engine is happy and will run all day with no extra noise or heat.
Modified 62 Tempest 389 Tri-Power, 700R4 transmission, Ford 9 inch with 3:50 gears, 28 inch tire. 70MPH is 2000RPM. Again can drive all day with no issues.

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  #23  
Old 10-25-2020, 08:44 PM
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Originally Posted by i82much View Post
i kinda feel like real classic hit rods are supposed to be a little rough around the edges!
Me too, when my 69 GTO was stock and street driven it had a M21 and 3.73s from the factory. Used to do road trips with friends in High School. Line of mussel cars going camping. None of those small block Chebby's could keep up on those long hills.
But all those cars were loud with plenty of gear. The way they were meant to be.
Went to High School at the perfect time. Started in 80 so all the cool mussel cars were 10-15 years old and cheap. We had rows of mussel cars and lunch time drags.
I would do anything for a picture of the full parking lot today. Did not know how good we had it.
In those day you were not anything unless you were driving some fast American iron.

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Old 10-26-2020, 05:50 AM
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RPM equals Gear Ratio x MPH x 336 divided by Tire Diameter.

If you have a good converter you'll barely see any increase in RPM at 70 MPH. I have 26" tall tires, 3.42 gears and a 10" Continental converter. Cruises just a hair over 3000rpms at 70mph. With 28" tires it's just under 3000rpms. The engine is comfortable with that RPM all day long. I think modern vehicles with overdrive have spoiled most folks with that deal. Back in the 70's when I first got into this hobby my daily driver was a 1970 Roadrunner with 3.90 gears. The big 440 didn't mind that much aside from being a little thirsty, but most of that was my fault because I couldn't keep my foot out of it!.......

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Old 10-26-2020, 05:59 AM
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Originally Posted by Dragncar View Post
...
In those day you were not anything unless you were driving some fast American iron.
Yep. My Firebird and my buddy's LeMans were the only Pontiacs at my school when I was a senior ('86). Not a real big school though. There were Chevelles, Mustangs, Camaros, a Falcon, a '64 Chevy pickup, Dodge Demon (426 wedge), GTX, a Corvette, a Cougar, and a '74 454 El Camino that was surprisingly fast for being all stock except for some headers.

And then there was the infamous "submarine" Celica. So named because the school was directly across the street from a park on Lake Washington that had boat ramps. The owner of the Celica parked at the top of the boat ramp and started a makeout session with his girl. Somehow the shifter got bumped into neutral and the car rolled down the ramp and into the lake.

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  #26  
Old 10-26-2020, 06:36 AM
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I've got 3:55 gears behind a TH350 with 26" tires on the street. For me it's too much on the interstate and keep up with traffic. I'm currently building a new motor and will most likely go with a 4L80E. It might be a perfectly safe thing to do (I really don't know) but listening to the 3K plus buzzing doesn't let my brain relax to enjoy the ride.

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Old 10-26-2020, 09:27 AM
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Quote:
Originally Posted by Cliff R View Post
RPM equals Gear Ratio x MPH x 336 divided by Tire Diameter.

I have 26" tall tires, 3.42 gears and a 10" Continental converter. Cruises just a hair over 3000rpms at 70mph. With 28" tires it's just under 3000rpms. The engine is comfortable with that RPM all day long. I think modern vehicles with overdrive have spoiled most folks with that deal. .
....... X2

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Old 10-26-2020, 09:47 AM
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Originally Posted by Dragncar View Post
Me too, when my 69 GTO was stock and street driven it had a M21 and 3.73s from the factory.
I did not realize that the 3.73 rear gear was a factory option on a 8.2 10 bolt PONTIAC rear axle. I always thought the jump went from 3.55 to 3.90 for the 8.2 Pontiac rear axles. Same deal with 3.90 jump to 4.33 instead of a 3.90 jump to a 4.11 gear like a chevy axle. Did you buy your vehicle with that axle from the factory?

Tom V.

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  #29  
Old 10-26-2020, 09:54 AM
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Correct Tom,

3.73 not available in the original 8.2 that came in 69 GTO's.

3.23 was common and standard for most base models, 3.55 is seen often, then the jump to 3.90 and 4.33

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Old 10-26-2020, 10:48 AM
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Don't forget it is not uncommon for a electric tach's accuracy to vary at different indicated RPMs. Especially known for it at a lower indicated RPM. And then the obvious converter slippage at steady state cruising speed if it applies.
But don't forget the effects of vehicle weight, and the unknown aerodynamic drag at speed on the vehicle.


.

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Old 10-26-2020, 11:47 AM
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With 3.23s and a 275/60 I'm sitting right at 3000rpm @ 75mph. That's about as slow as you wanna travel on the highways around here.

3.55s on up are pretty miserable on the highway for extended periods of time. If the car isn't going to see a lot of highway, it'll be fine.

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  #32  
Old 10-26-2020, 12:27 PM
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2 of my 3 68 to 70 400 cid auto Goats had 3.55 gears and even with a good bit hotter then stock Cam in them it is a great ratio for a 400 as 3200 rpm or better on the highway is right where the torque band starts to come on real strong!

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  #33  
Old 10-26-2020, 01:40 PM
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Quote:
Originally Posted by Cliff R View Post
RPM equals Gear Ratio x MPH x 336 divided by Tire Diameter.

If you have a good converter you'll barely see any increase in RPM at 70 MPH. I have 26" tall tires, 3.42 gears and a 10" Continental converter. Cruises just a hair over 3000rpms at 70mph. With 28" tires it's just under 3000rpms. The engine is comfortable with that RPM all day long. I think modern vehicles with overdrive have spoiled most folks with that deal. Back in the 70's when I first got into this hobby my daily driver was a 1970 Roadrunner with 3.90 gears. The big 440 didn't mind that much aside from being a little thirsty, but most of that was my fault because I couldn't keep my foot out of it!.......
X2. I agree with Cliff. I think modern vehicles have spoiled people. So much of what I read on different forums has to do with making an old car behave like a new one. I like the way old cars operate (with more HP/Torque of course) and If I want sometning to drive/behave like a new car (like my wife's new Ford) I'll buy a new car. Don't even have to covert ''em to EFI, they have it along with 600+/700+ horsepower. They also have no pesonality like my old '68 GTO. Enough, back to the OP's concerns.

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  #34  
Old 10-26-2020, 04:40 PM
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Originally Posted by Tom Vaught View Post
I did not realize that the 3.73 rear gear was a factory option on a 8.2 10 bolt PONTIAC rear axle. I always thought the jump went from 3.55 to 3.90 for the 8.2 Pontiac rear axles. Same deal with 3.90 jump to 4.33 instead of a 3.90 jump to a 4.11 gear like a chevy axle. Did you buy your vehicle with that axle from the factory?

Tom V.
I was the 3rd owner of the GTO, I ripped the teeth of of the original rear doing "chirps" all the time. It still had the tag on one of the cover bolts. I found a rear just like it in a 68 GTO in a junk yard.
But no, I have no idea where either came from originally.
Way back when I way 19 I decided to put the 9" with ladder bars and a Ford Top Loader 4 speed in the car I brought the broken rear end to the guys doing the work to cut off all the spring and shock mounts to weld on the 9" rear out of a 59 Ford truck.
They ground the parts off the GOOD rear end, not the junk one. I traded both those 10 bolts for motorcycle parts back then and kicking myself for it now. Both posi units.
I have a 10 bolt out of a 69 Lemans 350 car if I ever want to go back to stock.

Question, is the gear ratio on those tags on the cover ? I was 17 at the time, I want to say we either got the ratios from the tag or counted the teeth and did the math.

  #35  
Old 10-26-2020, 04:49 PM
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A lot what I can tolerate depends on the drone noises from the exhaust and how well balanced the driveline is. My hearing picks up droning a lot more than it use too, something I could tolerate a few years ago are not that fun now. But I towed a camper with my Yukon XL 3200 miles last year down to LA and back home to the Midwest, basically not using overdrive for the entire trip. 6 liter with a 4L80E and 3.73s. I ran 3000 rpm or more for the entire trip running 70-75. Honestly other than looking down at the tach it wasn’t noticeable. I could totally live with that vehicle and no overdrive. My T/A has a quiet enough exhuast 3000 for an extended trip would be doable with it too. Some of my other cars, ugh! Am I there yet???!!

Tire size makes a huge difference on this stuff. Even the dynamic rolling radius causes the final RPMs and mph to vary some. Some tires squat more and using the overall height isn’t all that accurate calculating RPM and mph. Measure from the axle down to the ground and compare that number to the advertised overall height give you an idea how close it will end up. Sometimes the tire construction combined with the load rating can loose/gain some rpms out on the road.

3.55s are a LOT better than 4.10s out on the highway. One of my cars has 4.10s and 30.2” tall tires and a 4200 stall. I don’t think I could drop below a 3.55 on that car. It loves the 4.10s. I think I could live with 3.55s though. With the big tires and 4.1s it goes down the road about the same as one of my 3.55 geared cars with 26” tires (275/50-15s).

A friend running a 70 Judge ran 3.23s with 14” rally 2s and went to 15” wheels and 3.55s and you could hardly notice any difference.

I have a lot of 3.23 gear cars. I would drive them anywhere. Sometimes I will use the 255/70r15s and that act like a 2.9ish gears set. I think the 3.23s quickly get a little sluggish with tall tires though. With the short 26-27” tall tires I like the 3.23s. Most of the time, if the car has has much HP, I would rather run the 3.55s and the taller tires. Then have a option of a swap to a short drag radial on the 3.55s and make them dig in, or run the taller 29” + tall tire and get a decent highway cruising rpm. We run 255/70R15s (29.1”) and 295/65R15s (30.2”) to get some better cruising rpms. Some of the 275/60-15s I have had are tall enough for 3.55s. Others feel like they make the engine turn harder than what you would expect.

On a A body with the 3.23 BOP 2 pin carrier connected to much power it is kind of shady. I don’t recall any aftermarket 8.2 carriers that correct that. 3.36 and the 4 pin carrier is a lot better. 8.5” it isn’t an issue.

I bought a car that the owner claimed had the factory 3.90s, the previous owner also said that he had never been passed. Lol. I asked Never? Really? He said Yep. I just speeded up. I knew something was up, 14” tires and 3.90s. After 100 that is zinging. Sure enough, I took it apart, someone put 3.23s in it. Shorter tires I like 3.23s or 3.36s. Tall tire 3.55s or 3.73s. 3.90s and 4.10s it starts getting to be to low to enjoy. Blows my mind Pontiac did 4.33s and 14” wheels!!!


Last edited by Jay S; 10-26-2020 at 05:01 PM. Reason: Edit
  #36  
Old 10-26-2020, 05:12 PM
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Heck my high school 409 Impala had a 29" cheater slick and 4.56s and drove all over town on the freeways! But now I agree we've gotten spoiled with OD transmissions.
79 Chevy truck we had had 3.73s form the factory and had 28" tall tires on it.

But when I had the RAIV head 455 in my TA and 3.42s and a 26" tall tire I would not stay with the traffic flow on Houston highways was screaming too much. And when I swapped the RAIV head 400 in it the 3.42s had no balls on the bottom end.

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  #37  
Old 10-26-2020, 05:17 PM
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The few mods I have made to my 64 GTO have been for the most part using older parts, like the 9" Ford Axle, 8.2 axles did not live in my vehicle. The 9" axle also has a lot more ratios available and is a bunch stronger.

I drove the car for several years as a stocker and after the third 8.2 rear axle, and 2nd Muncie trans, started modifying the vehicle for more durability and better overall drive-ability. A lot easier to move the lever on the shifter one more time vs swap the axle when I want to go on a trip. Car will never be sold out of the family so I have no problem with personal mods on the vehicle.

I do like the 5 speed a lot and if I did not have already a perfect 2.75 to 1
9" "soft locker" rear axle I might have gone with a 6 speed.

But to each his own.

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  #38  
Old 10-26-2020, 06:40 PM
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3.54:1 Dana60 with a 455+060 is no fun at 70 MPH, until you get the 4L80 4th gear, then it is FUN; 2500 rpm at 75 mph fun. Slingshot to 90 mph on Converter.

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  #39  
Old 10-26-2020, 06:45 PM
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A LOT more people are paying attention to Transmission Gears, rear axle ratios, etc on today's driving of 1960s and 70s vehicles.

Michigan has a 75 MPH speed limit and many go 10 mph over that on quiet rural divided highways like I-69 in Michigan.

Tom V.

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  #40  
Old 10-26-2020, 09:19 PM
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I'm on both sides of the fence. I completely understand the attraction, and overdrive swaps in classic cars are the most popular upgrade I've seen in the last 10 years and still going strong.

But there is still the old school in me, and I don't mind a little bit of gear in a car, especially a runner. I've always considered gears in the mid 3's a very nice compromise for a driver with some performance mixed in. But I also like to run 27-28" tires on the cars too. If I can go 65-70 at 2800-3000 I consider that an acceptable compromise that gives me a reasonable highway speed. I don't feel like I need to keep up with traffic. There is always another lane they can use.

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