What are my RPM's please?

[mark22]

Hi everyone, I've recently cquired an awesome 65 GS 3spd floor shift. I've got no tach and no overdrive, so I wanted to know what speeds I can safely drive at without stressing the motor.  I feel like the motor is screaming at 70 mph, and I want to make sure I'm not pushing the nailhead at unsafe levels if I don't have enough gear for highway cruising. Any feedback is much appreciated.

Thanks!

[dsags]

Mark22, the manual transmission cars had a 3.36 rear ended gear as standard. Assuming that’s what is in your car and that your tires diameter is about the same as original (26.8ish) then your RPM is about 3000 at 70 mph.

Dan

[mark22]

Thank you, Dan. By chance, is 3rd year on the 3spd a bit taller than on the 4spd transmission? May I kindly ask the redline rpm on this car? I?m guessing somewhere around 4500-4800 but would like to be sure. It sounds like I shouldn?t be driving this car faster then about 65-70mph if I don?t want problems.  It?s such a nice cruiser!

[dsags]

The top gear in all the transmissions was a 1:1 ratio. No overdrive. The engine was rated at 325 hp @ 4400 rpm. Personally would not go beyond that. That said 65-70 is a nice cruising speed in our cars. They can certainly go faster for short periods without doing any harm but that area around 70 is where I stay.

Dan

[WkillGS]

Hi Mark, congrats on the purchase and welcome to the site!

There are rpm/speed calculators easily found on the net. Here's one:
http://www.advanced-ev.com/Calculators/TireSize/
As Dan said, 3.36 is the standard rear ratio (yours could have an optional ratio), and trans is 1:1 ratio in high gear.
You'll need to input tire size as it is a critical factor.
By going to a shorter or taller tire, you can change the engine rpm at a given mph. Some guys even put large diameter tires on their car for a long out-of-state highway trip.

I've had 4.11 gears in my blue 66 GS for decades. With the larger 275/60-15 rear tires, I'd be buzzing the 425 at 3000 rpm at only 60 mph, which was fine when speed limits were 55.  I made numerous trip out of state (from Pa) to attend shows such as the GS Nats in Kentucky and the Car Craft Street machine Nationals in Indy and Springfield Ill. The motor was content buzzing along for hours on end. I finally switched to a 3.42 rear gear which increased my speed from 60 mph to 73 mph at the same 3000 rpm.

[TrunkMonkey]

Buy a cheap tachometer and run it temporally and make note of RPM range in each gear to the MPH range, then you will not be thinking about it all the time your driving. 

You can pick them up for under $25.
Simple to install.
One wire to the negative post on the coil, one wire to power on the fuse block and a ground.

[GS66]

Mark, congratulations on your GS! Any pictures you can share? My first car was a 66 GS 3 speed, great cars!

[elagache]

Dear Mark22, Dan, Walt, and mid-60s Buick owners of all kinds of reasons,

Hi everyone, I've recently cquired an awesome 65 GS 3spd floor shift. I've got no tach and no overdrive, so I wanted to know what speeds I can safely drive at without stressing the motor.  I feel like the motor is screaming at 70 mph . . . .

As Dan and Walt have pointed out, you aren't running your engine anywhere close where it would be damaged.  However, you are running into something of a paradox that the auto makers hadn't fully appreciated in 1965.  When your engine is over 3000 RPM, it is producing more power, but on the freeway it takes less power to maintain a steady speed.  In 1965 freeways were still mostly a novelty and this issue of running engines well out of their optimal conditions wasn't an issue.  After the two oil crises of the 1970s, auto makers started to provide transmissions with overdrive.  That significantly reduced fuel consumption and reduced noise on the freeway.

In a way, we are "spoiled" by the quiet of modern cars on the freeway.  My 1965 Buick Special wagon was my daily driver for essentially all my adult life and I simply put up with the freeway noise.  When I had my wagon restored mechanically, I upgraded the transmission to a TH200-4R with overdrive.  It makes a world of difference on the freeway.  These days even Ford Model-Ts are getting overdrives.  If you would like to drive your classic significant distances on the freeway, fitting an overdrive one way or another is definitely something to think about.

Cheers, Edouard 

[mark22]

Thank you to everyone who responded. I just love the car! It?s a zero option car. No PS or AC. 3 spd bamboo cream post car. It is just a beauty to drive and I definitely post a picture when I get back to a computer!

Thank you all for the warm welcome. I really enjoy the Buick community!