Highway driving....RPMS

[Bad Sport]

Bad sport is mostly right

I would have been more righter, lol, if I hadn't left out a sentence.

 

[HEMI-ITIS]

Glad you asked....I conducted this very experiment on my buddy's driveway a while ago...

Suregrip marks.....
View attachment 724545


and a Pegger......
View attachment 724546
This was NOT an experiment!

Hopefully that concludes today's lesson.

 

[451Mopar]

My '69 Coronet was an A-833 4-speed, 3.54:1 Dana and 27" Diameter (255x60x15) tires.
75 MPH would have been 3,300 RPM.
Installed the LGT-700 (Keisler SS-700) 5-Speed transmission that has 0.68:1 Overdrive, Now 75 MPH is 2,243 RPM.
http://legendgt.com/Products/lgt-700/

The Passion Performance A-855 5-speed has a 0.70:1 overdrive ratio
The TKO-600 can be had with a 0.64:1 Overdrive ratio, not sure about swap kits?

 

[69sunfireGTX]

the TKO-600 has 2 options for the overdrive ratio's. .64 OD or the .82 OD The .64 is a long throw compared to the .82

 

[threewood]

So, in today's world, if your not doing 70-75 on the highway, you get run over....my 69, 383, 4 speed car pretty much screams at those speeds.....does that mean I have 3.55 gears? (Or higher)? Is there simple way to find present gear ratio? If wanting highway cruiser, what should I be running?
PS....running 295/45/18 on rear
Thanks

I have 3.55 rear gears, 295/50-15 tires (26.6" tall) and at 65 mph I am turning 3100 rpms. 70mph is about 3250 rpms.

 

[747mopar]

I have 3.55 rear gears, 295/50-15 tires (26.6" tall) and at 65 mph I am turning 3100 rpms. 70mph is about 3250 rpms.

Yeap, that's exactly where I was with 3:55's before the 6 speed.. now it's 1,800-1,900 rpm at 80 mph lol.

 

[koosh]

Ok guys, FINALLY warm enough to get under car and mark driveshaft....it turned 3.5 revolutions, to 1 revolution of the tire...BOTH wheels rotated forward.....
So, I have 3.55 gears? Suregrip?
If I want highway cruising, do I want 3.23s, or 2.96s?

 

[33 IMP]

You have a suregrip.
3.55 gears are a good compromise gear, biased toward street performance, 3.23 is the best compromise, decent acceleration, decent revs on the highway. 2.76 or 2.93 are freeway flyers, but off- the-line will suffer. You have to decide what you want, how you plan to use the car, and what compromise you can live with.
I also believe that two series gears are hard to find used, and impossible new, but I may be wrong about that.

 

[Dennis H]

Jesus Chrysler this is painful. Like described, plant your right foot and count the streaks. Don’t like laying under the car with a crayon, etc. i have never known or cared about offset or tire diameter. Put a Tremec in and be done with it. 1935 @ 65 w/SST.

 

[koosh]

Jesus Chrysler this is painful. Like described, plant your right foot and count the streaks. Don’t like laying under the car with a crayon, etc. i have never known or cared about offset or tire diameter. Put a Tremec in and be done with it. 1935 @ 65 w/SST.

Send me over a blank check, I'll put the Tremec in.....not all of us are Rockafellers....

 

[koosh]

You have a suregrip.
3.55 gears are a good compromise gear, biased toward street performance, 3.23 is the best compromise, decent acceleration, decent revs on the highway. 2.76 or 2.93 are freeway flyers, but off- the-line will suffer. You have to decide what you want, how you plan to use the car, and what compromise you can live with.
I also believe that two series gears are hard to find used, and impossible new, but I may be wrong about that.

Thanks......I'm finding that out about the 2 series gears....cant find em.....probably will have to suffer with 323, has to be somewhat? Better than 355

 

[Dennis H]

Send me over a blank check, I'll put the Tremec in.....not all of us are Rockafellers....

That’s me! How did you know.

 

[moper]

There's not much of a difference between .23 and .55. If you consider the engine "screaming" (with the understanding that a: it's a car from an earlier era and it will be noisier and b: the 383 is a short stroke, long piston engine and designed to be driven for hours at 3500rpm) then you need to save up and change the transmission. I'd suggest an A833OD as a good alternative that is lower cost and basically bolt in, give or take. You need one out of a truck or van. Have the bellhousing hole enlarged for it, and bolt it in. You'll need to take care with the shift levers and adjustments of the rods, but it's an OD drop in that will make a difference for less than a second 8 3/4 pig.

 

[koosh]

There's not much of a difference between .23 and .55. If you consider the engine "screaming" (with the understanding that a: it's a car from an earlier era and it will be noisier and b: the 383 is a short stroke, long piston engine and designed to be driven for hours at 3500rpm) then you need to save up and change the transmission. I'd suggest an A833OD as a good alternative that is lower cost and basically bolt in, give or take. You need one out of a truck or van. Have the bellhousing hole enlarged for it, and bolt it in. You'll need to take care with the shift levers and adjustments of the rods, but it's an OD drop in that will make a difference for less than a second 8 3/4 pig.

An overdrive tranny is cheaper than a set of rear gears?

 

[33 IMP]

The difference between 3.23 and 3.55 is around 9%, so 3000rpm with 3.55 goes to around 2750.
I think what moper is saying is that a factory overdrive 833 is a lot cheaper than a five speed tremec.
The difference between 3.55 and 2.93 is around 17.5% so 3000 rpm goes to 2450.

 

[koosh]

The difference between 3.23 and 3.55 is around 9%, so 3000rpm with 3.55 goes to around 2750.
I think what moper is saying is that a factory overdrive 833 is a lot cheaper than a five speed tremec.
The difference between 3.55 and 2.93 is around 17.5% so 3000 rpm goes to 2450.

Ahhh......ok thanks

 

[koosh]

There's not much of a difference between .23 and .55. If you consider the engine "screaming" (with the understanding that a: it's a car from an earlier era and it will be noisier and b: the 383 is a short stroke, long piston engine and designed to be driven for hours at 3500rpm) then you need to save up and change the transmission. I'd suggest an A833OD as a good alternative that is lower cost and basically bolt in, give or take. You need one out of a truck or van. Have the bellhousing hole enlarged for it, and bolt it in. You'll need to take care with the shift levers and adjustments of the rods, but it's an OD drop in that will make a difference for less than a second 8 3/4 pig.

So......"383 is a short stroke, long piston engine and designed to be driven for hours at 3500rpm", your saying this is normal and ok? Then......maybe I should just leave things be.....its been long time since I had my 1st RR, and just dont remember the motor "screaming " that much WAY back then! Lol

 

[moper]

I'm saying they were sold with a warranty in everything from school busses and trucks to family wagons to performance cars - and they all had the same lower ends. But the cars (and owners of the time did not consider fuel economy as a big deal, and the transmissions only had three speeds. My '65 A body had a slanty, with a 3.23 and 13" wheel and tire package. 50 years after it was "new", I was bombing it down the highway at 75-80 with no tach. Not a big deal. My old 2bbl 383, with 85K original miles, a cam, 4bbl, and 175hp nitrous plate ran down the road at 4500+ for over an hour quick frequently because I was dating a girl at a college 150 miles away.
As long as the oil pressure reads fine (assuming a gage not a light), and the temps don't creep up, the highway rpm is not a significant issue. You won't shorten the service life by 50% or anything. You will use more gas, in the long run it will wear out a smidge faster, and it will be noisier in the cabin. But you won't hurt it if it's good to begin with.

 

[INTMD8]

3.55's wouldn't bother me at all with no overdrive.

Once drove a 78 Trans Am from California to Illinois, 4 speed with 3.73's holding it at 5000rpm through every tank of gas.

That didn't bother me (or the car) either

 

[HEMI-ITIS]

4:10 and 31 inch tall tire I'm about 3k RPM @ 60mph.