Too Many RPM's

[Ron Mullins]

I have a 1982 J-10 pickup that I put a mildly built 360 in and a T18 four speed with a 6.23 to 1 first gear. I have 3.73 axles and 33 inch tires. On the expressway when doing 65 MPH I'm already turning 2600-2700 RPM. I have a Dana 20 transfer case. I don't want to have to change axle gear ratios to make it more road drivable: does anyone have any suggestion?

[yossarian19]

Change axle gears, change tire size, or put in an overdrive transmission.
Guess you could drive slower.
That's about it.

[babywag]

2600-2700 is fine why do you think it's not road driveable?
That's pretty much the rpm range how they came when new.

A lot of folks are used to more modern 4 speed autos and manuals with much lower rpms, and think these old things are screaming down the hwy.

[Cecil14]

http://www.grimmjeeper.com/gears.html

Measure your tires (center of hub to ground x 2), and throw everything into the calculator. Also be sure to check your speed with a GPS; unless you've had your speedometer calibrated, it's probably off.

RPM vs speed is controlled by three things, and three things alone: tire size, axle gearing, and transmission ratio (assuming 1:1 t-case). If you don't want to regear your axles, you can either swap in an OD transmission (AX-15/NV3550 are good choices) or run taller tires. With tires, don't assume the number on the sidewall is the real height, measure it to know where you're truly at.


aa

[joe]

2600-2700 is fine why do you think it's not road driveable?
That's pretty much the rpm range how they came when new.

A lot of folks are used to more modern 4 speed autos and manuals with much lower rpms, and think these old things are screaming down the hwy.

X2
One mans too much is another's just right. For usability IMHO you're in the range you want to be. It's a 36 year old Jeep truck not your mom's Lexus. For drivability and general use be glad you have 3.73 gears cause those ain't stock in an 82 J-10. If this is really about gas mileage rather than drivability your only real options are axle gear swaps or install an OD trans. You'll have to do the math to figure out when/if the payback date for the swap investment costs comes in to play. I'd be glad for the 3.73's. Reasonable all-round usable gears for decent hwy rpm range and performance yet still decent grunt for off pavement work and still fair for towing. If you can do the set-up work, cheapest route would likely be trading your gearing for someone with stock 80+ J-10 gearing (2.73 or optional 3.31's). Actually the cheapest route if mpgs is your main concern is just "slow down". I know nobody wants to hear that ...but You'll find the reasonable to crap mpg break-over point is at about 60-65 mph. On 35 year old truck I vote keep the 3.73's and adjust your driving habits.

[FSJunkie]

You've got to be kidding me.

My Marlin runs 3600 RPM at 75 miles per hour and I've driven it thousands of miles across the country with it like that. The old engines are designed to run along at 2500-3500 RPM all day long. Bog them down much lower than that and they won't have enough power to push their big square heavy brick butt against the wind or up hills without downshifting.


2600-2700 RPM at 65 MPH is perfect. That's what my Wagoneer does and....guess what....I've driven it thousands of miles on interstates at 75-80 MPH like that and it LOVES it. Very good highway gearing.

[jeepman1]

2600-2700 is fine why do you think it's not road driveable?
That's pretty much the rpm range how they came when new.

A lot of folks are used to more modern 4 speed autos and manuals with much lower rpms, and think these old things are screaming down the hwy.

Amen

[tgreese]

2600-2700 is fine why do you think it's not road driveable?
That's pretty much the rpm range how they came when new.

A lot of folks are used to more modern 4 speed autos and manuals with much lower rpms, and think these old things are screaming down the hwy.

+1. Quiet exhaust, insulate the floor to make it quieter and drive it.

[FSJunkie]

Engines can be quiet at 3000 RPM....

But not when people put big exhaust pipes on them with loud mufflers.

Not when people put open element air cleaners on them that don't muffle carburetor noise.

Not when people put a fixed or flex fan on them that roars away.

Not when the engine, driveshaft, or engine accessries are poorly balanced and vibrate.

Not when the u-joint angles are wrong from suspension modifications and vibrate.

Not when people put aggressive tires on them.

.....meaning the most popular modifications.

Before I started driving my Wagoneer cross-country for hundreds of miles a day I removed the Magnaflow muffler I had and installed a stock muffler plus a resonator because I didn't want to isten to BBBWWWWAAAAAAA!!!!!! for 17 hours straight.

[rang-a-stang]

because I didn't want to listen to BBBWWWWAAAAAAA!!!!!! for 17 hours straight.

... but that’s the sound of America!!

[tgreese]

...
Before I started driving my Wagoneer cross-country for hundreds of miles a day I removed the Magnaflow muffler I had and installed a stock muffler plus a resonator because I didn't want to isten to BBBWWWWAAAAAAA!!!!!! for 17 hours straight.

Very sensible. Saves your hearing too.

[FSJunkie]

Motorweek back in the day tested the interior sound level of a new Wagoneer Limited at 55 MPH to be approximately 70 decibels, which was well within average for all cars of the time. 70 decibels sustained over more than a few hours is enough to cause slight impacts in hearing sensitivity.

That's at 55 MPH. Now speed up to 75 MPH and you're likely pushing close to 80 db. Add a loud exhaust or remove some of the original sound deadening material and 90 db is not out of the question. That for a few hours will definitely harm your hearing.