Topic: Any dyno'd 4bangers yet?

[Clem]

5.38 gears? Can you even cruise down the highway with those? I have 35's and stock 3.73's and I turn around 2600 rpm at 70 mph.

Here ya' go...

http://www.csgnetwork.com/rpmcalc.html

35 + 5.89 @ 60 mph = 3300 rpm. That is figuring a final output of 1.1. Obviously, that changes if you still have a 5th gear.

[Mozman68]

yea....I usually don't question Jeffy one bit, but that chart gearing seems a little too low for me as well.  It may give you the optimal power band, but not sure how comfortable it would be for highway driving.  Based on where I'm at right now with 4.10's and 31's, I think the 4.88's will keep me at the same right or only slightly worst with 35's (and the added weight of my axles and armor).  I'm willing to give up a tiny bit of power so I don't have to re-gear when I throw in a new engine....hopefully next year!!

[jfrabat]

heh..I have 4:10s and 31s..oh ya all factory gearing.   I could use a little more power when I'm 5th, most of the time have to downshift into 4th on a windy day.

That makes 2 of us!

[95yjman]

That makes 2 of us!

I have had a 4.0 throttle body for almost a year now and have just been to lazy to install it. I need to do that, isn't it true you get a little more power in 5th?

[Rob the plumber]

I did not notice any real difference with a 4.0L throttle body. It might be worth 2-4 horsepower that you will never really feel. It is when you add a header, free flowing exhaust, better air intake, electric fan, and a throttle body you might feel a small difference.

[Jeffy]

5.38 gears? Can you even cruise down the highway with those? I have 35's and stock 3.73's and I turn around 2600 rpm at 70 mph.

yea....I usually don't question Jeffy one bit, but that chart gearing seems a little too low for me as well.  It may give you the optimal power band, but not sure how comfortable it would be for highway driving.  Based on where I'm at right now with 4.10's and 31's, I think the 4.88's will keep me at the same right or only slightly worst with 35's (and the added weight of my axles and armor).  I'm willing to give up a tiny bit of power so I don't have to re-gear when I throw in a new engine....hopefully next year!!

Doubters?   

Here are charts with RPM's and vehicle speeds.  The sweet spot for the engine is anywhere between 2700-3500RPM.  Around 3300RPM is probably the best since you won't fall too low when going up hills and such.  BTW: these are for a 5-speed AX-5.  You can see 4th is pretty much useless with the 3.73's as well as 5th.  3rd is a bit too short at 3300 but you could rev it to 3500RPM and get it to 65mph at least.





Here's a stock Manual:



Here's a stock Auto:



Now what gear ratio seems to get an auto back to stock?

[jfrabat]

Jeffy,

Your auto with 4.88:1 is a little weird!  I think you may need a new tranny!!! 

Felipe

[Clem]

Doubters?   

    

Hehe... 5th gear is over rated. My YJ never liked it and tossed the stupid little snap ring at the end of the gear cluster several times. I live in Albuquerque, so 5th would be useless. It was nearly useless in Texas with more atmosphere. I figure that I really ought not be kicking a trail rig down the road at much over the posted speed limit anyways... Something red and on 35's usually turns heads without adding low flying...

[Clem]

Oops, I forgot to mention that somewhere along the way, I did the math on 27 inch tires and 4.10s and came up with 5.89 as being a similar power band for 37's... Guess what size my next tires will be? 

[Rob the plumber]

I personally need to be able to cruise at 70 mph on the freeway in Detroit. You get run over if you don't. I also don't like the idea of buzzing the motor at 3500 rpm for an hour or more down the freeway. I do however think I need a little more gear than the 3.73. I am keeping my eye out at the boneyard for an 8.8 with 4.10's.

My turbo also makes plenty of torque, so I don't need as much gear either though. On the trail 4-low works just fine.

[jcsanders79]

I have an auto with 33's and 4.88 gears.  There is a good chance that when I upgrade my lockers I will be putting 5.38's in it.

[Mozman68]

I personally need to be able to cruise at 70 mph on the freeway in Detroit. You get run over if you don't. I also don't like the idea of buzzing the motor at 3500 rpm for an hour or more down the freeway. I do however think I need a little more gear than the 3.73. I am keeping my eye out at the boneyard for an 8.8 with 4.10's.

My turbo also makes plenty of torque, so I don't need as much gear either though. On the trail 4-low works just fine.

You hit the nail on the head there....people forget that we have a speed limit of 70 here...which means the average is probably around 80.....Jeffy is just sitting in CA traffic half the time....

[Jeffy]

You hit the nail on the head there....people forget that we have a speed limit of 70 here...which means the average is probably around 80.....Jeffy is just sitting in CA traffic half the time....

The difference is that with more torque and hp, you can flub the ratio a bit more.  Changing gearing ignores the engine.  If you have more torque can subsequently, run a higher ratio then you normally would since you have a lot more torque available at any given RPM.

Out here on I-5 the speed limit is 70mph but you'll still get SUV's trucking at 80mph.  Although some go faster.  I still wouldn't want to drive a lifted Jeep at 80mph though.  I have and it's not fun.  A good gust of wind will still shove you around.

[Mozman68]

I think mine will ride a lot better once modded....I'll definitely have a lower center of gravity with the new axles....and the long-arm should ride a little better...also adding a new steering box to tighten things up....

[aw12345]

How do you think you will get a lower center of gravity with different axles? You are going from 31" tires to 35 " tires or bigger seems to that raises the center of gravity unless you use these highline fenders and hack the rear wheel wells it will sit higher than it does now. Sure a good long arm lift kit helps handling , but then wider tires and the rims to make them fit tend to make the front want to follow grooves in the road more.  Wanna have fun try to swerve for somebody that cuts in your lane on the freeway at 75- 80 mph gives new meaning to white knuckling it