High RPM at relatively low speeds

[Ranger16]

I'd check that Tach. When I installed my Sun Super II, I forgot to check the switch and got the same surprise you did. Switched it to 8 cyl. and all was well.

 

[66 Sat]

What does the engine sound like? Does it sound like your doing 4000 rpm? Also what does it rev to? If you can rev it to 8000 rpm then it's probably the tach....

 

[Dale Lucy]

I'm gonna get a different tach

It sounds like I am in second gear when I'm going 60

Dale

 

[Fran Blacker]

Any way your shifter rods are in the wrong holes on shifter or are on trans wrong?

 

[mopar 3 B]

Down load a speedo app to your cell phone and see what it says. You need to verify the speedo first. After that its just a matter of doing the math.

 

[Randy Marsh]

As already stated either the tach or speedometer is off. My Chevelle had 4.88 gears and didn't turn 4k at 60mph. If I recall correctly it was mid 3k's at that speed. If you're clutch was slipping that bad(and you didn't notice) you would have been informed by the fire department or been on a flatbed by now.

It sounds like you've been around the block before. I have a hard time believing that your ears can't tell the difference between 3k and 4k. I also would think that you'd know if you were really doing 80. It'll be interesting to see what this winds up being.

 

[dvw]

Any way your shifter rods are in the wrong holes on shifter or are on trans wrong?

You know I had forgot about this possibility. As a kid doing my 1st clutch job I flipped the shift levers
The pattern ended up being 3, 1, 4, 2. Thus the original poster says it takes off good in 3rd gear????
Doug

 

[AR67GTX]

I did the same thing on a Ford Toploader once - installed the transmission lever upside down on the 3/4 shaft. It took me a couple miles to realize something was crazy wrong as my rpms would increase when I shifted from 3rd to 4th.

I have a 427 Corvette with 4.11 rear and it doesn't rev nearly as high in 4th gear at 60s as is being indicated by the OP.

 

[PRHeads]

Down load a speedo app to your cell phone and see what it says. You need to verify the speedo first. After that its just a matter of doing the math.

I like that idea!!

It could be the tac and the speedo are off.

 

[Dale Lucy]

Well, the speedometer and tach are both crap.
Installed a new tach, and used an app for vehicle speed

60mph @2750ish RPMs. Just what it is supposed to be. I guess that is what happens when you havent driven a real (mopar) car in years, you forget what they are supposed to sound like.

All is well again with the universe.

Dale
SW MI

 

[Kern Dog]

As already stated either the tach or speedometer is off. My Chevelle had 4.88 gears and didn't turn 4k at 60mph. If I recall correctly it was mid 3k's at that speed. If you're clutch was slipping that bad(and you didn't notice) you would have been informed by the fire department or been on a flatbed by now.

Randy, your math seems off a bit too though.
I have 3.55s in my Charger with 28" tires and at 60, I am running around 3000 rpms.

 

[PRHeads]

Well, the speedometer and tach are both crap.
Installed a new tach, and used an app for vehicle speed

60mph @2750ish RPMs. Just what it is supposed to be. I guess that is what happens when you havent driven a real (mopar) car in years, you forget what they are supposed to sound like.

All is well again with the universe.

Dale
SW MI

 

[Randy Marsh]

Randy, your math seems off a bit too though.
I have 3.55s in my Charger with 28" tires and at 60, I am running around 3000 rpms.

I just checked one of those gear calculators. It says 3514rpm. 28" tire, 60mph, 4.88 gear, with a 1:1 4speed. Maybe you've got a little bit of convertor slip. A couple hundred rpms isn't uncommon.

 

[dcala84141]

I have 3.23 gears with stock F70 14 tires and at 3000RPM I’m during 75mph.

 

[alleycat81448]

As has been mentioned already......
First step should be to verify the rear gearing.

“If” those are determined to actually be 3.54’s, the tac is off(or you have really really short tires).
For example: 60mph, 3.54’s, 26” tires = 2745rpm driveshaft speed.

On the other hand......
60mph, 4.56’s, 26” tires = 3536rpm
And 4.88’s would be 3785rpm.

As has been mentioned already......
First step should be to verify the rear gearing.

“If” those are determined to actually be 3.54’s, the tac is off(or you have really really short tires).
For example: 60mph, 3.54’s, 26” tires = 2745rpm driveshaft speed.

On the other hand......
60mph, 4.56’s, 26” tires = 3536rpm
And 4.88’s would be 3785rpm.

Likely your 3.54 gears are more like 4.56.
Probably didn't change the little stamped tag.

Likely your 3.54 gears are more like 4.56.
Probably didn't change the little stamped tag.

 

[alleycat81448]

example- i have 354 dana 4 speed-70 miles a hour is 3400

 

[dcala84141]

example- i have 354 dana 4 speed-70 miles a hour is 3400

What size rear tire u running?

 

[Stephen dd]

So, new to me '69 GTX conv, 440, 4-speed, Dana rear with 3.54 gears, 15 inch tires all around. Driving to the gas station today, and to the local body shop, I was seeing approx 4000 RPM @ 60 mph in 4th. I can easily take off at a stop sign in 3rd.
Just the way it is? Could someone have re-geared the 4-speed (is that even possible)?

Dale
SW MI

I have the same drivetrain, and no way can I 'easily take off in 3rd gear".

 

[Ceedawg]

Making me think about mine before I get it all together. 4.1 Dana-4 speed-Hemi 775-14 tire. One car show is about 50 miles away, maybe I should use the 3.54s? Anybody know what rpm for either gear @60?

 

[Fran Blacker]

Had 4.10's 26.5" tire, 15 miles on the highway knew 4.10's were to much. Never mind 50 miles. Listening to your engine scream for mercy and getting passed by everybody. I was clogging the highway. Had 3.54's in before drove 400+ miles to see Niagara Falls and back to Rochester NY in one day for a NeHOA meet.