Gear Ratio for 31" tires at altitude-G Wagoneer

[Dave Jeeper]

I have an 89 Grand Wagoneer with 94k miles. I put a 4" lift on and 31" tires. I am not planning on going to bigger tires now or in the future. Axles are Dana 44 front and rear, both open diffs and geared 3.31. Howell TBI and HEI distributor (base timing is set to 19 degrees BTC because of altitude). Engine is stock aside from TBI and HEI, no changes to the cams, etc. Automatic tranny (3 speed unlocked) and the kickdown lever is correctly adjusted. I just replaced my charcoal canister and idle is better now, still have a mild stumble and mild hesitation. I have not done a compression check. Engine passes emissions and does not blow smoke.



I am at 5300 foot altitude (20% less air density, so 20% less oxygen and 20% less power compared to sea level).


Acceleration getting on the highway from the entrance ramp is not that fast. I worry about getting rear ended as I get up to speed. Many of the drivers here are not very polite and don't make way for slower vehicles. I don't plan to do alot of off road with this Jeep, I have lots of XJ's for that. I am considering re-gearing for better acceleration and putting a limited slip in the rear for driving on ice. I have a spare limited slip carrier from a 1988 XJ small Cherokee rear Dana 44 with 30 spline axle shafts. That carrier is good up to 3.73 gearing if my research is correct. It came with 3.54 stock XJ gearing.



I have about 150 pounds of cargo in the rear, but no other extra weight (no after market bumpers or winch).


What gearing do you recommend? Gas mileage is poor anyway so that is not my main concern. I am driving around town and on the highway about 20 miles per day.



Will the limited slip carrier from the XJ work in the G Wag rear Dana 44? If I go above 3.73 numerical gears, then can I use a thick cut ring gear with the limited slip carrier from the XJ?


How will my top speed be affected by gear change? I normally don't drive over 75 or 80. I sometimes take the SJ up into the mountains which are at an even higher elevation and the highway is a very steep grade.


Would 4.10 gears rev too high on the highway? Will 3.73 give enough acceleration, especially on paved mountain highway passes with 4 people in the Jeep?


Looking forward to hearing from people's experience, especially anyone in Colorado or at altitude elsewhere. Thanks in advance.


David

[wiley-moeracing]

The most I would go is the 3:73, acceleration will be better but sacrifice a little on the top end speed( will do it but at a higher rpm). 3:55 if your more worried about top speed.

[joe]

If it were me for your intended use with 31" tires I'd go with 3.73's. IMHO it's a good all around use compromise gear. Does well for performance on the street, not to high RPM at hwy speeds, still good for 4x4 dirt work and decent for not too heavy towing. If larger tires might be in your future you might consider 3.92's or 4.11's.

[tgreese]

Better to decide what engine speed you want whan traveling on the highway. Easy to calculate based on the tire size and gearing, using one of the many online gearing calculators.

The higher numerically (deeper) you go, the better the Jeep will feel in terms of power and on the trail. Within limits, as you go loer numerically (taller), the Jeep will get slightly better mileage and will seem more at ease on the highway.

Note that modern drivers often think that their engine is going to blow up at engine speeds that are perfectly acceptable on the highway. Quiet exhaust, quiet tires, plenty of insulation in the floor.

https://www.novak-adapt.com/knowledge/gearing/

[FSJunkie]

Note that modern drivers often think that their engine is going to blow up at engine speeds that are perfectly acceptable on the highway. Quiet exhaust, quiet tires, plenty of insulation in the floor.

Halleluiah somebody said it.

[Dave Jeeper]

It currently takes me 25 to 30 seconds to go from zero to 55 mph. That is with a mild uphill on the on-ramp, 31" tires, 3.31 gears and 5300 ft altitude, Howell TB fuel injection and HEI. Base spark advance is 19 degrees: 9 BTC plus 10 BTC for altitude. I am thinking that there is some problem with the engine. I am not sure how fast the vehicle should accelerate, but it must be faster than it is now. The transmission is very smooth, no lurching and no hard shifts. No slippage visible on the tach that I can detect.



The engine idles a bit rough and hesitates a little on acceleration. I replaced the charcoal cannister and the engine runs a little smoother now (less vacuum leak). I will check the vacuum to the brake booster for leaks when I have a chance. If the EGR is problematic, would that only affect the engine when cold or both cold and hot? I also need to check the stock air intake to make sure that the cold air and exhaust stove doors are functioning correctly. I will also check the passenger side down-tube exhaust valve to make sure that it is opening.


Any comments on acceleration?

[wiley-moeracing]

You seem to have an issue or issues, it should not take that long to accelerate to 60. I used to drag race against a olds diesel wagon that would do the 1/4 mile in 18.6 seconds at 83 miles mph bone stock, yours should do way better than that. I would get a proper check up on the motor and then a tune up and start there.

[Dave Jeeper]

I pushed the check valve into the grommet on the vacuum brake booster today and my idle smoothed out and I got more power. I am trying to find a replacement grommet. Doorman is the only one that is listed as being for the G Wag, but it doesn't look to be of very good quality.

[FSJunkie]

You've got to be kidding me. My stock Wagoneer goes 0-60 MPH in 11 seconds, timed by a drag strip.

[rocklaurence]

OK, consider an alternate route for better performance. A higher stall torque converter-2000rpm. It will cost less than replacing front and rear gears and you get to keep the lower RPM on the highway. You'd likely want a larger/more efficient cooler.

[gopher_6_9]

Yeah something is off, with 32 inch tires and 3.31 gears I accelerate just fine. He'll I've chirped a tire a time or two since shift kit was put in.

[wiley-moeracing]

Replacing the torque convertor with a high stall one will not get you more "performance" over a gear swap. It only raises the rpm lock up level to put you higher in the power curve of your motor, good if you have a bigger cam that comes on at a higher rpm level but not really worth it on a stock cam/motor. A stock 12" convertor would be the best option, runs cooler and comes into lock up at a lower rpm, which is where the cam is.

[J20 project]

As stated, 3:73 is a good choice. Ran that ratio in a variety of FSJs over the years and liked it. I disagree on the limited slip being a "good" choice for driving on ice..Having driven on ice for all of my life, open diffs are best. Does sound like you may have issues...does a 89 have a cat?



J20

[Dave Jeeper]

New cat, muffler and tailpipe. I am continuing to work on the fuel injection. Waiting for some warm weather to confirm TDC regarding the new HEI distributor to make sure that timing is set correctly. Installed a new vacuum charcoal canister, started getting carbon out of the tailpipe shortly after that. Just disconnected the canister and cleaned the fouled O2 sensor. Installed a new high altitude EGR.


Will update things in a couple weeks after testing. I thought that 3.92 gears (I think that is the split for carriers) might be the best ratio for me. Not sure yet if I will regear or not.

[FSJunkie]

As stated, 3:73 is a good choice. Ran that ratio in a variety of FSJs over the years and liked it. I disagree on the limited slip being a "good" choice for driving on ice..Having driven on ice for all of my life, open diffs are best. Does sound like you may have issues...does a 89 have a cat?



J20

Agreed.

I live in the second snowiest city in the United States, second to Albany, New York.

Limited slip is great for keeping you from getting stuck. It keeps the tires grabbing and keeps you moving by preventing one tire from spinning independent of the other, but it comes at a price: both tires will spin together if you apply more power. It's twice the traction and it keeps you moving forward, but both tires spinning means the back of the Jeep goes sideways. It can send you all over the road. You have to be ready for it. Otherwise, an open differential will just spin one tire and while that makes for less traction, at least you don't go sideways.

I'll still take a limited slip in bad weather. The limited slip can make it squirrely, but it gets you home. The open differential is easier to drive, but can get you stuck.