Gear ratios and bad advice

Chris

Administrator
Staff Member
Sep 28, 2015
36,207
Salem, Oregon
It's ridiculous. I can't tell you how many times I've seen/heard something along the lines of "I want more power but I don't want to go above 2000 rpm. Wastes too much gas and hurts the engine."

Ignorance at its finest. You have to learn from those who actually have experience with these engines and can't base your decisions off of 2000 rpm in a Jeep straight engine.
Hurts the engine? Haha... wow... some people are so stupid.

And in addition to that, if you want good fuel economy you shouldn't even own a Jeep / truck / 4x4.

Honestly, it amazes me how dumb some people can be.
 
  • Like
Reactions: Brantley

Chris

Administrator
Staff Member
Sep 28, 2015
36,207
Salem, Oregon
Many people think, the lower the rpm's, the better mileage. They just do not know how engine efficiency affects mileage.
They also don't realize that constantly running at low RPMs isn't good for an engine anyways.

I've run into this before though, where some people assume that going over XXXX RPM will do damage to your engine. Ummm no, that's what a rev limiter is for dumbass!
 
OP
B

Brantley

TJ Enthusiast
Yep, try driving at 2,000 rpm all the time for years. Let's see how it's running when it's filled with carbon inside the combustion chamber from all that lugging. I'd rather run my engine all day long at 3,000 than 2,000 and I think my engine would thank me for it.
 
  • Like
Reactions: StG58

Chris

Administrator
Staff Member
Sep 28, 2015
36,207
Salem, Oregon
Yep, try driving at 2,000 rpm all the time for years. Let's see how it's running when it's filled with carbon inside the combustion chamber from all that lugging. I'd rather run my engine all day long at 3,000 than 2,000 and I think my engine would thank me for it.
It would! I always try to explain to people that engines were designed to be run at higher RPMs.

A good point is some of the sport bikes I've owned in the past. Some of them would rev to 17k before the rev limiter kicked in. I'd always have to explain to people that the rev limiter is there for a reason, and that if the engine wasn't designed to safely rev to 17k RPMs, then it wouldn't be able to do that from the factory.

But then they assume, "oh, well you shouldn't ride it at high RPMs very often". Really, and where did you get your information on that?

There's a reason that it's called, "the old Italian tune up".

I've taken apart engines before that came from crappy little economy box cars. You almost always find tons and tons of carbon build up inside of them. While I'm sure there's a variety of factors that contribute to that, I think a large part of it has to do with the way people drive. Shifting at 2000 RPM, bogging the engine down, etc.
 

UpperMI

TJ Addict
Supporting Member
Jun 9, 2016
1,560
San Carlos, CA
This is one of the more informative threads I've read on this forum. Tons of good advice. Since reading this I've tried to run in 4th gear a little more when on the freeway as I have 31's with 3.73 gears. But the one thing I can't figure out is why the shift light comes on really early in the rpm range. I think that's why people don't want to rev their engines higher. "the light told me to shift". So I get some of the confusion.
 
  • Like
Reactions: Chris and Brantley
OP
B

Brantley

TJ Enthusiast
This is one of the more informative threads I've read on this forum. Tons of good advice. Since reading this I've tried to run in 4th gear a little more when on the freeway as I have 31's with 3.73 gears. But the one thing I can't figure out is why the shift light comes on really early in the rpm range. I think that's why people don't want to rev their engines higher. "the light told me to shift". So I get some of the confusion.
I think it's because in theory, to some people low RPM means less gas. Unfortunately, Chrysler installed that stupid shift light which only leads people incorrectly. It comes on in my Jeep at 2,000 rpm which if I drive by, is absolutely gutless. I removed the bulb because of that.

Sucks though, once someone gets stuck in their ways of refusing to rev higher than 2,000 or so, it's nearly impossible to convince them to drive differently and try revving a little bit like they should.
 
  • Like
Reactions: UpperMI

UpperMI

TJ Addict
Supporting Member
Jun 9, 2016
1,560
San Carlos, CA
I think it's because in theory, to some people low RPM means less gas. Unfortunately, Chrysler installed that stupid shift light which only leads people incorrectly. It comes on in my Jeep at 2,000 rpm which if I drive by, is absolutely gutless. I removed the bulb because of that.

Sucks though, once someone gets stuck in their ways of refusing to rev higher than 2,000 or so, it's nearly impossible to convince them to drive differently and try revving a little bit like they should.
I've noticed that my jeep shifts better with higher rpms. I used to be one of those people that would always shift around 2,000-2,200 rpm. Since moving the shift point up to 2,700-3,000, the jeep just feels better. Smoother transition and the feel on the clutch is better.
 
  • Like
Reactions: Brantley
OP
B

Brantley

TJ Enthusiast
My AX15 loves 3,000 rpm shifts. If I shift from 1st to 2nd at around 3,500, it doesn't like to come out of 1st quite as easily. That's been on both of my AX15s so it must just be a trait of that transmission. 3,000 seems to be about perfect though around town and when I'm merging on the freeway I kick it up to 4,000-4,500 just for the extra acceleration power. Works pretty well. Of course, I shift to 5th around 3,000 or so because I would have to go like 85-90 mph to reach 4,000 in 4th.
 
  • Like
Reactions: Chris and UpperMI

Chris

Administrator
Staff Member
Sep 28, 2015
36,207
Salem, Oregon
I don't even know how you could drive a Jeep and shift at 2000 RPMs. I tried that once just to see what it was like, and it was seriously miserable. People were honking at me and flipping me off. I couldn't even get out of my own way!
 

lovemachine

TJ Enthusiast
Supporting Member
Feb 13, 2017
985
Indiana
Well, it would be tough to snap a pic with one hand on the wheel and a beer in the other :D
Nah. With the Currie currectlync, I can be driving 85mph and take my hands off the wheel, and my rig doesn't wander whatsoever.

It can be done, not smart, but I could do it :)

That's the beauty of having quality parts!
 
  • Like
Reactions: xxdabroxx and StG58

Chris

Administrator
Staff Member
Sep 28, 2015
36,207
Salem, Oregon
The people that shift at 2,000 rpm must be where the 4.slow nickname comes from, which I think is totally untrue. I'd say for being a 6 cylinder with 4wd the 4.0 is a pretty stout motor.


Sent from my iPhone using Tapatalk
It's really not bad at all, especially in the torque department. You're right, people drive them stupid, which is probably where that nickname comes from.
 
OP
B

Brantley

TJ Enthusiast
It also gets a bad reputation from Jeep installing 3.07 gears in probably 75% of them. Somebody who drives a completely stock Jeep on 3.07 gears revving 2100 at 70 and is clueless with Jeeps will tell you Jeeps aren't fast. What they don't know is that they have literally the worst gear ratio for the 4.0, even on stock tires.

I think all 5-speeds should have had 3.73 and all 3-speeds should have had 3.55. 4-speeds should have been 4.56. 3.07 should have never been involved from the beginning. A completely stock Jeep on the lower ratios works very well in stock form. Same as the Rubicon on 31's and 4.10.

As you all said, the 4.0 can be a great engine if it's geared properly, one knows how to drive it, and the engine is in good shape.
 
  • Like
Reactions: Chris
OP
B

Brantley

TJ Enthusiast
This also brings me to mention a funny conversation I was involved in that could maybe be helpful to someone.

On Facebook, I was talking with a genius who asks questions and then likes to turn down the answers people give him. Every week or so, he posts a picture of this Eaton blower kit for $2699 and asks if anybody has experience with it. Nobody answers, so he usually "bumps" it, and finally someone might answer, usually telling him to just regear the Jeep.

He has a 3-speed auto, 4.0, on 33's. apparently, he's been racing corvettes since he was 10 years old (he's 31 now), so I guess he thinks that makes him the master of all things Jeep, engines included. I, and a few others, have recommended just regearing to 4.10 and calling it a day. If he still thinks the performance is lacking, then do the supercharger. He refuses, the rpm would be "way too high." I always ask the same question, "what about when the tres were stock, were they too high then?" He never answers it, he only claims that 33/4.10 will keep the rpm too high. Today, the conversation ended up with me blocked because I wouldn't shut up about gearing. Fine, it's his Jeep, I really don't care that much.

I do wish I weren't blocked though so I could see him drop 3 grand on a Super charger when he's still ultimately going to want to regear when he realizes a supercharger on 3.07s is the equivalent of lipstick on a pig.

3.07 generates a ton of heat in those transmissions and isn't good for it. I say regear first to put the engine back in its normal operating range, then supercharge it or stroke it or whatever to get it to the power that one's heart desires.