[60over68400]

I'm wanting to put some 3.55's in my 8.2. I was wondering how driveable on the highway my car would be after putting them in? It would be through a turbo 400. I'm think I would be about 3000 RPMs @ like 70, is that a pretty good assumption? I almost would like to stick with something a little higher because I do drive it on the highway. Any help or suggestions would be greatly apprieciated thanks.

[6t7gto]

60over,
i took 3.55 out of my car and went with 2.56.
cruise the highway at 2200 rpm now.
check this out...
http://www.tciauto.com/tech_info/calculators.htm#7

david

[Jeffzilla]

I have 3.43 's in my 79 firebird behind a turbo 350 and it does just fine on the highway.

[Barrier Blue]

Originally Posted by 6t7gto

60over,
i took 3.55 out of my car and went with 2.56.
cruise the highway at 2200 rpm now.
check this out...
http://www.tciauto.com/tech_info/calculators.htm#7

david

Must be one of those '67 Lemans rear-ends.

[Formulabruce]

I left the 3.42:1 rear and installed a bolt in 2004R with .67 4th gear and lock up converter
1700 at 55

[cblandin]

Here's the deal. Most of us are used to driving much newer vehicles and overdrive trannies have been around for a LONG time now. I find that my 3.23's are annoying in my 67 Bird as compared to any new car I own. This is exacerbated by the fact that I have a "nice" rumbly exhaust (as do most of us), which makes it even louder. Finally, add the rattles, creaks, and groans found in 35+ year old cars and it isn't exactly a Lexus ride. The RPM in my BMW at cruise isn't much different tht my Firebird, but my BMW is loads quieter, and has an extra 1000 rpm until redline. I've always said the biggest benefit to an overdrive tranny was never mileage - it was driving enjoyment. One question - what gears do you have in there now? Accelerate to 3000rpm and drive there for a while on the freeway - do you find that objectionable?

[TR]

Originally Posted by cblandin

Here's the deal. Most of us are used to driving much newer vehicles and overdrive trannies have been around for a LONG time now. I find that my 3.23's are annoying in my 67 Bird as compared to any new car I own. This is exacerbated by the fact that I have a "nice" rumbly exhaust (as do most of us), which makes it even louder. Finally, add the rattles, creaks, and groans found in 35+ year old cars and it isn't exactly a Lexus ride. The RPM in my BMW at cruise isn't much different tht my Firebird, but my BMW is loads quieter, and has an extra 1000 rpm until redline. I've always said the biggest benefit to an overdrive tranny was never mileage - it was driving enjoyment. One question - what gears do you have in there now? Accelerate to 3000rpm and drive there for a while on the freeway - do you find that objectionable?

You've nailed it down dead-on. Time was, 3.55's were once universally considered an all-around good compromise between highway cruising and max acceleration. A good gear that a musclecar owner can live with in daily life.

Fast forward to having owned OD equipped cars since '85. Having our cake and eating it too. I put 4.10's in my 6-speed '94 Z28 and still turn barely 2000 RPM's @ 70 MPH. I drive my '70 Judge with 3.55's, and even around town at 45-50 MPH, I still instinctively attempt to shift it out of 4th into a non-existant 5th. Can't believe we used to consider this a compromise gear. A RA IV w/4.33's would be near insane on the highway.

[b-man]

I had a set of 2.56 gears in my '64 Tempest, they came in it from the factory along with the 215-cube six and 2-speed auto. I kept them when I transplanted a 455/TH400 combo into it, absolutely wonderful on the highway. Here in So Cal if you can't maintain at least 75 to 80 MPH on the freeways for long distances you'll get run over.

After a few years the 2.56 gears gave up and I swapped in some 2.93 gears. Not long after the swap I was longing for those 2.56 gears.

My brother has a '69 350 Firebird that came with 2.78 gears. We swapped in a warmed-up 350 HO engine and changed to a 3.42 rear from a second-gen T/A. He said it was barely liveable on the highway.

In my opinion if the car is going to see any open-road miles 3.08s would be the lowest I'd consider. I would consider 3.23s to be right on the borderline, you'll definitely hate the 3.55s.

[Dryseals]

My Corvette had the 2.73 gears and a 700R4, I swapped to 3.75 gears for the fun of it and have never looked back (275 40-17s). It sounds great on the highway.

The wifes street truck has 4.10 gears and a 700R4, a blast to drive and good manners on the highway (275-60-15s)

My 67 GTO had 3.90 gears and I loved the way it sounded cruising on the highway.

I just bought a 12 bolt posi with 3.55 gears for the 68 bird, 4 speed BW. I can't wait to here it roar.

If you like the engine noise and the sound of a good exhaust, go for it. If you want a quite ride, keep the gears down or buy a daily driver. I love the sound of a high reving motor, maybe thats why I'm looking at an older 911 for a work car. To each his own.

[uneasyrider]

Originally Posted by TR

You've nailed it down dead-on. Time was, 3.55's were once universally considered an all-around good compromise between highway cruising and max acceleration. A good gear that a musclecar owner can live with in daily life.

Fast forward to having owned OD equipped cars since '85. Having our cake and eating it too. I put 4.10's in my 6-speed '94 Z28 and still turn barely 2000 RPM's @ 70 MPH. I drive my '70 Judge with 3.55's, and even around town at 45-50 MPH, I still instinctively attempt to shift it out of 4th into a non-existant 5th. Can't believe we used to consider this a compromise gear. A RA IV w/4.33's would be near insane on the highway.

LOL! Yep, I've looked for that "5th gear" before too. I would agree with the above and add that I have a close ratio 4spd and 2.73's in my '74 TA and I like the combo generally. Better would be a 5spd with an od 5th and 3.55's BUT I didn't have the cash for the 5spd. I turn about 2,300 on the highway at 70mph and it sure helps the mileage. I have a healthy 462 in it and it's getting 19mpg on the highway if I haven't got my foot in it and that's the hard part. The only thing I don't like about it is reverse in tight parking spots because reverse uses 2nd and it loads up if you have to do much backing or there is a hill etc.

[tom s]

I have 3.55s in both my 69 RA V T/A and GTO.That IMO is as low as you would like in a steet car.I drive to a lot of shows that are 30-50 miles away and usually in the slow lane at 2800 RPMs.My 421 lemans has the tremic with 3.90s and is very drivable on the freeways.Tom

[Junkyard Dog]

So, Tom, you would recommend 3.90 with the Tremec? What does that do to your first gear? Doesn't the Tremec have a really low first gear comperd to the Muncie M-22?

[Formulabruce]

Originally Posted by cblandin

Here's the deal. Most of us are used to driving much newer vehicles and overdrive trannies have been around for a LONG time now. I find that my 3.23's are annoying in my 67 Bird as compared to any new car I own. This is exacerbated by the fact that I have a "nice" rumbly exhaust (as do most of us), which makes it even louder. Finally, add the rattles, creaks, and groans found in 35+ year old cars and it isn't exactly a Lexus ride. The RPM in my BMW at cruise isn't much different tht my Firebird, but my BMW is loads quieter, and has an extra 1000 rpm until redline. I've always said the biggest benefit to an overdrive tranny was never mileage - it was driving enjoyment. One question - what gears do you have in there now? Accelerate to 3000rpm and drive there for a while on the freeway - do you find that objectionable?

EXCELLENT POST!!!

2004R tranny HIGHEST ratio output auto ever made (89 T/A pace car, and many more had them) .67:1 output, then the lock up converter!!

[BILTIT]

My 3.73's and th350 amount to about 3400 rpm at 65-70mph (no speedo). Sure pulls hard when passing but always seem to run out of rpm before i am done? Go figure!

[baron_]

i've got 3:55 in my '67 goat

i run 3100 or so going 65 mph on the highway
and by the time i'm doing 75, it's near 3500 or so...so that's definitely too much for extended periods

it's a little much (you'll have to drive 65)...but could be worse
a good compromise i think, unless you plan on doing a lot of highway driving

[uforacing]

Having done alot of driving with the 3.08-3.55 gears I will say one thing. if all you want to do is the "I" then 3.08 or lower or get a 200r4. Out here the Interstates are 75mph. I have driven the GTO with 3.55s 500 miles one way and I ran 65 with it.

One of the things I like is when im driving one of the cars to a event is that I am not in a hurry. I like driving the state routes thru the small towns and most of the speed limits are 65 or lower. Part of the fun is getting there.

[Tripower455]

I have 4:11's in my 12 bolt, and turn 2800 rpm at 80..............with a Tremec!

[marauder]

I didn't like my 3.42 gears on the highway, around here the speed limit is 70 and everyone does 80. I installed a 7004R and now the 3.42s are just right.

[David Jones]

Mine has 3.55's and a Turbo 400 (400CI). 70mph is about 3200 rpm and the car will happily do that and more for as long as you can pump gas into it. Thats the way it was back "in the day". Its them damn loud ass mufflers most folks run that turd up a good highway run. My 20" Super Turbos keep it sane and quiet enough to listen to the radio (I never turn it on) or hold a normal conversation. I would go no further than a 3.23. Acceleration is to much fun.

[carcrazy]

Had 4.33's in a 67 GTO and it was pure misery on the hwy! I was in my mid 20's at the time and didn't care. Have 3.73's in one car now and I don't like that much either. 3.55's are probably borderline if you do a lot of highway driving. (damn I sound old)