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post #1 of 12 (permalink) Old 01-27-2013, 06:25 PM Thread Starter
 
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Rear gear question

I just joined the forum. Not good at this yet.

I have a 71 gto with a 455(yc block) turbo 400 transmission and a limited slip posi and 3:73 gears. It seems like the engine is tacking to high. My question is do I need to change gears to maybe a 3:23 or a 3:31.

Thanks for any input.
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post #2 of 12 (permalink) Old 01-27-2013, 07:55 PM
 
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Standard rear axle for a 71 455 "YC" was a 3.07 ratio.

I'd probably go with the 3.23 if you plan on much highway driving.

The other option is to replace the trans with a 4 speed OD trans (700R4 or 2004R) and keep the 3.73 axle. The overdrive will knock your highway revs down about 33% and you'll still have that 3.73 "punch" off the line. Nice combo...

1968 Pontiac GTO
1983 Pontiac Bonneville (G) wagon
2008 Pontiac G8 base
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post #3 of 12 (permalink) Old 01-28-2013, 07:49 AM
 
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...Pontiacs make much more low end torque than chevys, we don't need those 4:10 gears to get up and go. Have a 12 bolt sitting on the floor with 3:55's and with the gas the way it is i may just leave it there and stay with the peg leg 2:56 thats in the car. i can lope down the freeway at 65-70 at 2200 rpm and still roast the 255's of from a 15 mph roll and get 13+ MPG. All depends on how you will be doing your driving.
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post #4 of 12 (permalink) Old 01-28-2013, 08:16 AM
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This - Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.

Have your cake and eat it too. Now I hear all the time that "Pontiacs" make so much torque you don't need deep gears" but..... The simple fact is gearing is a mechanical lever to move your vehicle and a car with lower gears will accelerate faster (if you can hook it up ). True that Pontiacs will run good with a higher gear ratio because of the torque they make but in the same car I think acceleration would be better with a 3:55 than a 2:56 ratio. Overdrive gives you the best of both worlds. Heck, back when Instigators car was new it had a two speed and highway gears. Now new cars have final drive ratios in the 4's and 6, 7 or more transmission ratios with multiple overdrive gears.

Now, overdrives aren't for everyone due to budget, perceived weight penalties or they just don't fit but having overdrive on my car changed everything. I can cruise at 70+ with 4:11's and stay with or pass traffic while cruising on the highway.

No offense meant at all Instig8ter, no doubt that big 455 makes enough beans to move your A body with authority with those gears and if your combo works and you are happy with it i wouldn't change a thing.



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post #5 of 12 (permalink) Old 01-28-2013, 09:10 AM
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Good points made, and totally valid. Everything is a compromise. That said, the most cost effective compromise for a 455 powered street car is simply installing a 3.07 or 3.23 gear. Overdrives rule, no doubt, and are the best solution for max performance AND cruising, but for simplicity, durability, and low cost, the 'right' rear end is hard to beat. Another thing: that 3.55 geared car that got the hole shot over the 2.56 car: well, I caught up to that guy when he was wound out at about 95mph, and kicked my 2.56 car into passing gear and hit 3rd at 107 and was gone. Who's the slow guy now?
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post #6 of 12 (permalink) Old 01-28-2013, 09:22 AM
 
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none taken Alky...old adage holds true "how fast do you want to go?...how much money do you have?". I love to cruise in my car, don't take it to the track, rarely even drop the hammer on it, live in rural area where light to light is usually a few miles so for the time being it's a good fit. Man i can just imagine the two speed hooked to the 326 WITH A 2:56 gear...LMAO, talk about peddling uphill both ways.
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post #7 of 12 (permalink) Old 01-28-2013, 11:15 AM
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Quote:
Originally Posted by geeteeohguy View Post
Good points made, and totally valid. Everything is a compromise. That said, the most cost effective compromise for a 455 powered street car is simply installing a 3.07 or 3.23 gear. Overdrives rule, no doubt, and are the best solution for max performance AND cruising, but for simplicity, durability, and low cost, the 'right' rear end is hard to beat. Another thing: that 3.55 geared car that got the hole shot over the 2.56 car: well, I caught up to that guy when he was wound out at about 95mph, and kicked my 2.56 car into passing gear and hit 3rd at 107 and was gone. Who's the slow guy now?
Lol, yeah I had a Buick way back when that would chirp the tires hard when I shifted from first to second gear at 60 and hit third at 100+ full throttle.

I also had to sell that one when every cop in town knew me by sight.
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post #8 of 12 (permalink) Old 01-28-2013, 12:29 PM
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I test drove a '65 GTO ragtop back in the day that had a 4 speed and 4.11 gears out back. It was a terror on the freeway onramp, but when I got on the freeway, the ting was screaming at 55-60 mph. Alky, Buick's of the late '60's and early '70's get less respect than just about any other make. It's too bad, because they are one of the fastest and best turned out cars of this era. Pretty hard to beat a GS or GSX with a 455 under the hood....no matter what your driving.
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post #9 of 12 (permalink) Old 02-01-2013, 08:42 PM
 
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I had 2.56 in my 67. I had 3.55 put in. I'm running about 3100 Rpm at 65. I decided to put a 700r4 in for the over drive gear. I should run under 2100 Rpm at 65 now.

I'm waiting for my new driveshaft. Then I will be ready for a drive.
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post #10 of 12 (permalink) Old 02-02-2013, 11:28 AM
 
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Well, now you all got me reconsidering if I should swap my 200 4R for the TH400 or not. With a 474 and 373 gears, the 200 does save fuel. I'm itching to get this thing to the track and friends all say the 400 is the best choice, I have a 400 for the car in the garage, but it needs gone thru before I use it. The 200 I have has had a lot of upgrades, but I think it was ran pretty hard before I got it and needs some work also. I was at the Buick GS nationals a few years ago and watched some hopped up turbo V6 Grand Nationals doing some awesome wheelstands, probably using the 200 4R. I know the 200 has a lower first and second gear than the TH400, but I'm not convinced how it would hold up at the track with a big V8 and sticky tires. Anyone ever used one for racing?
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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