Highway speed.
Race Director
Joined: Oct 2007
Posts: 15,818
Likes: 90
From: Fairfield, VA
Leadfoot nails it.
So a modern car w/ auto in Overdrive has locked up 1:1 w/ the tranny.
Cruising along 2000rpm or so.
A modern 5 or 6-speed manual is cruising along as well.
My '69 Camaro w/ 4:11's was a backroads car, no highways for me.
I guess the guy who put the gears in thought it was cool. It wasn't.
So a modern car w/ auto in Overdrive has locked up 1:1 w/ the tranny.
Cruising along 2000rpm or so.
A modern 5 or 6-speed manual is cruising along as well.
My '69 Camaro w/ 4:11's was a backroads car, no highways for me.
I guess the guy who put the gears in thought it was cool. It wasn't.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,573
Likes: 7,015
From: New Or-leens Loo-z-anna
I could be incorrect, but I think the line of thought in the original post, is "Why does my C-3 seem to be all wound out at 70 MPH", when my DD doesn't. And as we all know, overdrive is the answer. My C-5, with the M6 transmission, is loafing along at 1400 RPM, at 65 MPH, whereas the '77 Pontiac T/A that I used to own, with 3.23:1 gears and 27" OD tires was turning 2400 RPM at the same speed..........yeah, I know the speed limit is 55.
And you are right about the point of the original post: Do the math for us (let's use some uncomplicated numbers).....2,000 rpm verses 4,000 rpm for 100,000 miles.......how much "wear" does an overdrive transmission save on an engine compared to an old-school transmission (you will be amazed at the answer).
Last edited by doorgunner; Apr 20, 2015 at 07:13 PM.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,573
Likes: 7,015
From: New Or-leens Loo-z-anna
I'm now trying to keep my rpm above 2000 at 70 mph to balance power with engine vacuum.....it's important (but not a necessity) to keep the vacuum reading as high as possible for good fuel atomization in carbed engines (rookie observation).
Burning Brakes
Joined: Feb 2012
Posts: 925
Likes: 7
If you like your car now, get an overdrive 5 speed tranny and be prepared for a great new experience. Speed limit on I-95 where I am is 70. You need to go at least 75 not to be a mobile roadblock. 75mph is 2150 or so with 3.73s and 27" rear tires. Changes the car completely. Loud exhaust quiets down, engine noise reduced, engine run cooler and conversations can be had without shouting. If I had to do again, I would pair a 3.55 with my BB.
Drifting
Joined: Jan 2011
Posts: 1,853
Likes: 81
From: Hamilton Virginia
I have a 454 in my 76. The gears in it are 3:73s, which has me running about 65 @ 3000 rpms. I do not do alot of highway driving but, I would feel better doing 70 mph @ 2500-2700 rpms. So for now I am cool but if I run into a 3:36 rear that I can swap out at a good price, I will do so.
Team Owner
Joined: May 2001
Posts: 87,315
Likes: 1,585
From: Western NY
Drifting
Joined: Sep 2010
Posts: 1,412
Likes: 50
From: Laguna Niguel California
Yes back in those days we ran low gears for fun AND gasoline was 29 cents a gallon. Now I have 3.08's and cruise at 80 mph and 3400 rpm.
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Burning Brakes
Joined: Mar 2014
Posts: 904
Likes: 46
From: Crestline CA
Do you guy's know if some one makes a 5 speed gear set that will go in to the stock tranny housing? Keep it all numbers matching, just with a extra gear. ( Baker makes this for Harley's)
Last edited by dugsgms74; Apr 23, 2015 at 12:48 AM.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
496, T400, 3.36s, 28" tires, 70 mph is 3000 rpms... I'll run it at 3000 all day long and not think twice aboutit... 75 mph is about 3200 and I'll often run at this speed for shorter trips.. No problem..
For 3.70 and lower gears, a 5 speed OD swap would be an excellent move if you plan on a decent amount of highway driving..
That being said, this summer I'm road tripping about 3k miles in mine, no OD...and you bet your as$ I'll be running every bit of 70 mph the whole way...
For 3.70 and lower gears, a 5 speed OD swap would be an excellent move if you plan on a decent amount of highway driving..
That being said, this summer I'm road tripping about 3k miles in mine, no OD...and you bet your as$ I'll be running every bit of 70 mph the whole way...
Drifting
Joined: Sep 2014
Posts: 1,430
Likes: 59
From: Long beach NY
St. Jude Donor '15-'16, '18
In drivers Ed our car had guys who were already driving but with drivers Ed you could get your night license early. Our teacher was the football coach and we used to go on the NYS thruway. He used to tell us take ten and go. So we had 3 teenagers and a teacher riding shotgun doing 75 mph in class. He'd be arrested today.
1969/1971/2021 Coupes
Joined: Jan 2008
Posts: 2,212
Likes: 80
From: Port Huron MI
St. Jude Donor '09-'10-'11-'12-'13-'14-'15
Yep I agree. I remember cruising right around 55-65 on the highways in my dads new 72.