sinat01
NAXJA Forum User
- Location
- Preston county, WV
Plus its less strain on the drivetrain
-
Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.
Gearing/lack of power or speed question
- Thread starter ljobbins
- Start date
Plus its less strain on the drivetrain
So I just had a chance to look around the jeep and I pulled the spark plugs and they all looked great. Then I did a compression test:
#1-145
#2-155
#3-150
#4-148
#5-142
#6-140
So nothing crazy jumped out at me but if one of the parts stores has a lead down tester I can rent/borrow, I will do that tomorrow. I can double check my distributor is indexed right and make sure I have good spark on each cylinder and double check my fuel pressure tomorrow but if it all checks good like I think it will, I will be back to my original problem of something not being right. Any thoughts or suggestions? I know someone mentioned clutch earlier but it's brand new. I'm by no means a clutch or transmission expert, so is there a test to make sure the clutch is fully grabbing? I don't smell any burning from a burning clutch.
#1-145
#2-155
#3-150
#4-148
#5-142
#6-140
So nothing crazy jumped out at me but if one of the parts stores has a lead down tester I can rent/borrow, I will do that tomorrow. I can double check my distributor is indexed right and make sure I have good spark on each cylinder and double check my fuel pressure tomorrow but if it all checks good like I think it will, I will be back to my original problem of something not being right. Any thoughts or suggestions? I know someone mentioned clutch earlier but it's brand new. I'm by no means a clutch or transmission expert, so is there a test to make sure the clutch is fully grabbing? I don't smell any burning from a burning clutch.
denverd1
NAXJA Forum User
- Location
- Dallas, TX
Awesome compression. Wouldn't waste time/money on a leak down, you have issues elsewhere IMO
Sent from my SAMSUNG-SM-G930A using Tapatalk
Dang. Why did I have to read this post today? I'm on 33's with stock gearing and I was close to content with it. Thought about regearing "someday."
Now I'm convinced that I'm not doing right by my baby unless I do it this weekend.
I don't have the time (or money) for this!!
Now I'm convinced that I'm not doing right by my baby unless I do it this weekend.
I don't have the time (or money) for this!!
lazyxj
NAXJA Member #1310
- Location
- Los Angeles
Re-gearing isn't something to do without a bit of thinking and research.
No matter how it's done, it ain't cheap and it gets more expensive as traction enhancing devices are added.
It isn't something you can do yourself unless you really know what you are doing and have access to a variety of tools most do not already own.
The said, re-gearing is the most satisfying upgrade I have made yet.
One suggestion is to not undergear it, keep the cruising RPMs the same as stock, or even a little higher, you will get better mileage and it will be a lot more fun to drive.
I drove on 31"s, with 4.11s, for years and was happy with it but when upsizing to 33"s, it became doggy, one trip to Colorado was enough to convince me to to re-gear.
Changing to 4.56s straightened it up.
- Location
- Wasatch Range
When selecting the proper gear ratio for your rig, don't forget to factor in these real-world variables, most of which you will never see on a Gear Ratio Calculation chart.
Listed in no particular order:
All of these are factors which should be considered when making the decision on which gear ratio will best suite your rig, based on it's unique modifications and daily use.
Listed in no particular order:
- Tire size/wheel (increased weight/rolling resistance-factor current size and future)
- Transmission type (4 speed Auto vs 5 speed Manual)
- T-Case gearing (effective crawl ratio in 4Lo)
- Lift height (taller rig = more wind resistance)
- Armor (added weight and wind resistance)
- Axle swaps (1-Ton running gear/steering = added weight)
- Recovery gear (added weight and wind resistance/winch)
- Roof rack, roof tent, lighting (wind resistance, weight)
- Full size spare carry location (weight, wind resistance if roof mounted)
- Type of daily use (city/hwy travel, terrain/elevation changes, passengers, cargo)
- Off-road use (wheeling in sand/snow robs power vs slick-rock crawling)
- Towing frequency/trailer weight
- Elevation of use (engine makes more HP/TQ at sea level than at 5000ft)
- Age of engine (engine loses HP/TQ as it ages/mileage increases)
- Engine modifications/swaps (significant increase of rear wheel HP/TQ requires less gearing)
All of these are factors which should be considered when making the decision on which gear ratio will best suite your rig, based on it's unique modifications and daily use.
mvktr2
NAXJA Forum User
- Location
- S. Mississippi
The OP is driving a manual according to posts concerning the clutch. This means the stock differential gearing is 3.05 iirc. For comparison stock automatic ax15 equipped differential gearing is 3.55. Thus there is a significant difference between going to 4.56 from the two different starting points. It's a difference of 28% gearing increase vs 50% increase. OEM tires were 28" tall tires. Going from 28" to 33" tires is an increase of 18%. Compare that to the gear ratio increases. 50% (gear increase) - 18% tire size difference = 32% higher gear:tire ratio over stock. The math isn't completely linear but it makes sense that you'd run higher RPMs by 1/3 to attain same speeds as stock configuration.
Another possibility no one has mentioned is the option that your phone based gps speed is wrong?
As discussed there are calculators online that will give you all the information for figuring out what RPM you should be running at what gearing ratio/tire size. More useful still are the various spreadsheet style charts showing gearing ratios needed to match stock performance. The better charts give the input data for what type of trans or even trans gearing were used for formulation which is useful.
Another possibility no one has mentioned is the option that your phone based gps speed is wrong?
As discussed there are calculators online that will give you all the information for figuring out what RPM you should be running at what gearing ratio/tire size. More useful still are the various spreadsheet style charts showing gearing ratios needed to match stock performance. The better charts give the input data for what type of trans or even trans gearing were used for formulation which is useful.
mvktr2
NAXJA Forum User
- Location
- S. Mississippi
This is doing 80 with stock gearing with 33X12.50r15
What this doesn't show is the downshift and drop in speed by 10 mph on a moderate-medium hill or much more on more dramatic heels. I've run 3.55s on 32" and hate it driving in MS which isn't particularly hilly compared to some states and far from flat compared to others. Keeping 60-65 is hard on an engine in my configuration and I suspect is a contributor, having to work harder longer, to my recent engine failure. Running 75 on the interstate was much easier than 60 on 4-lanes thanks to the better rpm range it put the engine in.
That said I aint telling chickenbot he's wrong just that my experience is substantially different.
Well I’m still trying to track down what’s going on super slowly because I’m pretty busy with college projects and other activities I’m involved with. But on the freeway(southern California) my phone says 62 mph and I am definitely getting passed by cars going at least 15mph faster. I did run a full tank of that b-something cleaner someone suggested and it did help smooth out my engine a tiny bit but did not magically fix my problem.
And I’m not exactly worried about the rpms but more about my top speed with the pedal floored being in the high 50’s to low 60’s.
VAhasnoWAVES
NAXJA Forum User
- Location
- Lake City, Mi
questions...
- does the motor go through the full RPM range? by that i mean idle to rev limiter when in nuetral.
- what RPMs are you turning at 60 mph? both 4th and 5th.
- if you down shift can you power through the speed cap you are seeing in a higher gear?
and this is where my suspicion is...
- did you buy the rear axle or gear it yourself?
- and if you bought it, did you verify the gear ration?
assuming the motor and trans are in good health (its a 4.0 and AX15... either they work or they dont. lol), your issue screams tall gearing (low numerically). with 4.56s on 33s you should have no issues hitting 3k rpms and driving 80mph.
here is a pretty good calculator for you to take a look at:
http://www.grimmjeeper.com/gears.html
- does the motor go through the full RPM range? by that i mean idle to rev limiter when in nuetral.
- what RPMs are you turning at 60 mph? both 4th and 5th.
- if you down shift can you power through the speed cap you are seeing in a higher gear?
and this is where my suspicion is...
- did you buy the rear axle or gear it yourself?
- and if you bought it, did you verify the gear ration?
assuming the motor and trans are in good health (its a 4.0 and AX15... either they work or they dont. lol), your issue screams tall gearing (low numerically). with 4.56s on 33s you should have no issues hitting 3k rpms and driving 80mph.
here is a pretty good calculator for you to take a look at:
http://www.grimmjeeper.com/gears.html
VAhasnoWAVES
NAXJA Forum User
- Location
- Lake City, Mi
So no tach, so I couldn’t tell you what rpms I’m at. It idles just fine.
And I bought the axle with gears already installed. The first thing I did though was take the cover off and check it. Everything looked good and I double checked it was 4.56. I am going to buy a tachometer next week when I get back from a small trip and I’ll see what it says after l install it.
Similar threads
