[slowbird]

Just curious how people like 3.55 gears on the highway. What size tire are you running and what rpm you turning on highway?

[Ben M.]

I hated it. I had a '69 Lemans with 225-75R15 tires and toploader 3 speed. Per the tachometer it ran at 3300-3400RPM. The engine screamed and I was not a fan. Also made dropping gears to pass nerve wracking. Just the noise from the engine alone was enough to make driving a chore after about 30 minutes.

When the speed limit was 55 or if we aren't driving them 100 miles each way to work, it probably would be fine. Anything I wanted to drive somewhere far away, I wouldn't like it.

[Formulajones]

We daily drive our 69 Z with 3.55's and 27" tire. Works just fine in my opinion, and my wife doesn't mind it at all.

We daily drove it I'm guessing 4 years like that with a stock Muncie and probably logged close to 40,000 miles with some long trips mixed in before this year eventually installing a TKO600

Just not a big deal, but I'm used to driving cars with 3.73's and going across country. I grew up with cars and gears so it's just not a huge deal.

[slowbird]

Originally Posted by Formulajones

We daily drive our 69 Z with 3.55's and 27" tire. Works just fine in my opinion, and my wife doesn't mind it at all.

We daily drove it I'm guessing 4 years like that with a stock Muncie and probably logged close to 40,000 miles with some long trips mixed in before this year eventually installing a TKO600

Just not a big deal, but I'm used to driving cars with 3.73's and going across country. I grew up with cars and gears so it's just not a huge deal.

What cruise rpm you turning with the 27" tire?

[Formulajones]

Originally Posted by slowbird

What cruise rpm you turning with the 27" tire?

Most of the time I'd just put it on 65mph which is about 2900 rpm. On long trips across Arizona I'd do 70 and keep the engine around 3,000-3100. Keeping in mind this is a 4 speed application so no slippage (no torque converter)

On my old truck with 3.73's and 400 turbo, for 20 years we did cross country trips with that 2-3 times from the West cost to Cincinnati, Prescott to Sacramento several times, Cincinnati to Pigeon Forge a couple times etc..... I had a 30" tire on that one and it would go about the same, 65 mph at 2800 rpm but there is a little converter slippage figured in. Most of the time on the long trips I'd just put it on 70 mph and hit cruise control. The 454 didn't mind it at all and logged over 100k miles like that.

I guess I'm one of the few that's old school, that stuff doesn't bother me that much. That's how these old cars were built back in the day and no body minded then either.

[PunchT37]

Mine is almost dead nuts 3000 at 70. M/T et streets, 275/60/15`s. T400 with continental 10 inch converter.

[b-man]

With a stick shift you’d be turning 3092 rpm at 70 with a 27” tire.

With an auto trans you’d of course have some converter slippage that increases cruise rpm by whatever percentage of slippage in your combo. With say 5% slippage you’d be looking at 3247 rpm at 70 mph.

I remember back in 1976 when one of my high school friends bought a new Toyota SR5 mini pickup. We all thought it was the greatest thing in the world, all because it was one of the first affordable vehicles that came with a 5-speed stick. Plenty of folks were yearning for that extra gear for the highway by then.

[slowbird]

Originally Posted by PunchT37

Mine is almost dead nuts 3000 at 70. M/T et streets, 275/60/15`s. T400 with continental 10 inch converter.

Good info, thanks.
We currently have 4.11's and im working on making the car more street friendly for my dad. I know comverter plays a roll but im just not sure how much one slips going down the road at a steady pace.

[getmygoat]

A rule of thumb is you turn your gear ratio at 75 mph. e.g. 355's will be 3550 RPM at 75 mph. Note that tire size won't show up on the speedometer unless the owner has specifically changed the speedo gear to accommodate for the tire size.

A tire size is more likely to just cause the speedo to read low (for larger than stock tires).

I personally think 355s are too low for highway driving. Its better to get an overdrive or 3:08 or lower gear if you are planning to do significant cruising over 60.

A lot of people on this forum are more tolerant of noise and vibration than I am.

[milty]

I went to 3:55’s from 3:08’s when I also went to a built up 2004R from the TH400.... perfect combo for highway cruising while still keeping it decent for stoplight action. Retrospect, I probably would have just kept the 3:08s and TH400 and put the $$$ elsewhere.


Sent from my iPhone using Tapatalk

[Stuart]

Depends on your personal tolerance. I have 3.42 gears with a four speed, and it gets a little busy for me when driving for long periods on the highway and I starting wishing for a 5th gear.

[i82much]

3.54 dana 60, ultra wide ratio muncie, and 28” tires. i don’t cruise above 60, but i live in the country and it is easy to avoid the interstate.

used to run 3.90’s with the same tire, but speed limit was 55.

[Formulajones]

Originally Posted by slowbird

Good info, thanks.
We currently have 4.11's and im working on making the car more street friendly for my dad. I know comverter plays a roll but im just not sure how much one slips going down the road at a steady pace.

A lot of this is going to depend on your combo. If you run an automatic like most seem to, camshaft and converter selection make it a little more tricky on rear gear selection, especially with these Pontiacs and the torque they make.

Dad ran 3.73's in his combo for the better part of 30 years. Worked fine with his 455 and a nice Continental converter. When he switched to a 571 a few years ago, Kris at Continental couldn't build a converter tight enough for it. Dad was living out here in Arizona by then and we tend to drive long distances for events (300+ miles in a weekend) so he wanted to knock some gear out of it. Kris didn't recommend anything less than a 3.50 gear (less gear numerically makes the converter act looser). Even with the 3.73's the Continental was loose as a goose with a lot of slippage at the track and the gear change would have made that even worse. It didn't drive all that great either. With Continental gone by that point we went with TSP to try and tighten this thing up because 3.42's were going in. It took a second try with TSP to get a converter that couples up well enough to drive okay with 3.42's but I don't dare put less gear in it. That would just make the converter hell to deal with and probably another restall. We still need to hit the track with the new converter and 3.42's anyway for some testing, but so far on the street it's fine.
He cruises around 28-2900 at 65 mph with a 28" tire so there is a little slippage but not horrible (The Continental struggled to do 60 at the same rpm). We've done some long distance cruising with it and it's way better than the 3.73/Continental setup was.
The car isn't noisy or obnoxious at cruise either, it's actually very well behaved and pleasant to drive.

[blueghoast]

I cured that problem by removing my tach LOL

GT.

[geeteeohguy]

Originally Posted by slowbird

Just curious how people like 3.55 gears on the highway. What size tire are you running and what rpm you turning on highway?

I was OK with the 3.55's in my '66 GTO from '79-'94 because the National speed limit was 55mph. Stock height tires. It would buzz pretty good at 60, and 65-70 was not comfortable. When I toasted the 3.55's in my '65 GTO in 1990, I had them changed to 3.36. I would have gone to 3.23 or 3.08, but the carrier wouldn't allow it. I run 29" tall tires on this car today, and it's ok at 70. I pulled the stock 3.36 rear out of my '67 GTO (Th400 car) and installed a 2.56 safe-t-track. I love it. 21 mpg at 75-80 mph. 2450 RPM. 3000 RPM at 90 mph. I can keep up with the Nissans and Hondas now.
So, in a word, 3.55 gears on the highway suck. Big Time. Unless you have an overdrive set-up.

[Tom Vaught]

My Brother-in-Law had a new 1965 Olds 442 with 3.55 gears and drove the 150+ miles from Kansas City, Kansas to Gravois Mills, Missouri on the Lake of the Ozarks many times. He was running the speed limit in the 1960s of 70 mph. No issues whatsoever. Gas was 26 cents a gallon too.

I drove my 64 GTO down to the Lake of the Ozarks from a town in central Missouri daily and back and it had 3.90 gears at the time. About 60 miles each way, some engines just like engine rpm. Gas was cheap you were not breaking the bank with paying for gas (Sunoco 260) at the pump.

So I guess it depends on your tolerance level for exhaust noise (the Smitty Steel Packs were music to the ears).

Later in the 70s I went to Niagara Falls from Western Michigan (Three Rivers) many times but it was with a swapped in 2.56 gear/rear housing BECAUSE I could run 80 mph on the 401 highway and the engine was happy at that speed vs engine rpm.

So it depends.

Tom V.

[TCSGTO]

I have 3.42’s with 27-1/2” tall tires, automatic with a 9-1/2” converter, and 70 is tolerable for short stretches but 55-65 is more comfortable for a longer cruise.
It seems to use just as much gas cruising at 70/3200ish rpm as it does in the city.

[tom s]

I hated the 3.55s in both my GTOs.Tom

[i82much]

i kinda feel like real classic hit rods are supposed to be a little rough around the edges!

[Stan Weiss]

Originally Posted by Tom Vaught

My Brother-in-Law had a new 1965 Olds 442 with 3.55 gears and drove the 150+ miles from Kansas City, Kansas to Gravois Mills, Missouri on the Lake of the Ozarks many times. He was running the speed limit in the 1960s of 70 mph. No issues whatsoever. Gas was 26 cents a gallon too.

I drove my 64 GTO down to the Lake of the Ozarks from a town in central Missouri daily and back and it had 3.90 gears at the time. About 60 miles each way, some engines just like engine rpm. Gas was cheap you were not breaking the bank with paying for gas (Sunoco 260) at the pump.

So I guess it depends on your tolerance level for exhaust noise (the Smitty Steel Packs were music to the ears).

Later in the 70s I went to Niagara Falls from Western Michigan (Three Rivers) many times but it was with a swapped in 2.56 gear/rear housing BECAUSE I could run 80 mph on the 401 highway and the engine was happy at that speed vs engine rpm.

So it depends.

Tom V.

My brother's '65 GTO 4 speed conv had 3.90:1 from Pontiac. Gas was cheap and that I can remember it had a big tank. My '67 GTO 4 speed had more highway friendly gears from Pontiac, but I am sure that is because it had factory A/C.

Stan