Gear Ratio for 31" tires at altitude-G Wagoneer

[PlasticBoob]

I dunno, but I'll tell you that 32s with 3.07 gearing is great on the highway, but not so fun around town...although the 401 can still torque its way through the lousy gearing.

What about a helical limited slip on ice? I have heard nothing but good about those, and I have a Quaife sitting here waiting to go into my little project car.

https://mgaguru.com/mgtech/rearaxle/ra302c.htm

[PlasticBoob]

In any event, I think the best thing you can do for wintry conditions is invest in some winter tires. Numerous videos show that 2wd with winter tires beats out 4wd with all-season or summer tires...uphill, downhill, handling, braking, and even on ice!

https://www.youtube.com/watch?v=atayHQYqA3g

[Dave Jeeper]

Regarding lockers: I have 4 XJ's (small cherokees). 2 have ARB selectable lockers front and rear. They are definitely my favorite and are very expensive. I have Eaton? helical gear soft lockers on one XJ and they are slow to engage. They are supposed to work better if you keep light pressure on the brake to get the mechanism to engage. I would not buy them again. My stock XJ (not lifted like the others) has a limited slip in the back and it works great for slippery surfaces on the street. It gives more traction compared an open diff with 4wd which would spin one wheel in the rear on ice. I am not planning on rock crawling with my SJ so a limited slip is my choice. If I wanted to spend more, there is a locker available that is limited slip with an electric selectable locker function. Limited slip all the time and electric lockup available for when it is needed.


Lots of options, some cost less, some alot more.


I have been driving in snow and ice for 45 years and have had some kind of locker for the last 18 years or so.


I have never had the hard lockers like the detroits or lunch box lockers. The idea of the locker suddenly kicking in when not expected on an icy curve scares me.


David

[rws31]

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.

Have you pulled some spark plugs to see how they are burning yet? A fouled O2 sensor and carbon out of tail pipe sounds like a really rich fuel condition.

Sounds like you got serious problems to figure out as to why it runs like a pig. You can't re gear a pig and hope to turn it into a race horse.

[Dave Jeeper]

The plugs were fine for about 4 or 5 months and there was no carbon. Shortly after replacing the vacuum canister a few weeks ago is when it started fouling. It took about a week after the charcoal canister before it started throwing carbon out the tailpipe when idling. The carbon was visible on the sidewalk but not visible in the gas coming out of the exhaust.


I asked about regearing because I have never driven another SJ and did not know how they perform. I had owned a 1989 XJ which always accelerated slow at altitude with 31" tires. They redesigned the 4.0l engine after 1992 and then the XJ could run 31's without regearing. The responses to this post have given me info about the performance of my rig and I will try to improve that performance before making any gearing changes.


My calculations have shown that the effects of altitude account for twice the loss in performance compared to the increase in tire size when going from stock to 31". 4.23 gears would be needed to restore the original stock performance and that does not include the extra aerodynamic drag that occurs with the 4" lift. I know that they don't offer 4.23 gears, that was just a theoretical number from the calculations.


My 31" BF Goodrich KO2's are brand new by the way, so traction in snow is great. They are not studded though, so they slip when trying to accelerate on slick ice. The KO2's are the best tire that I have tried for all around performance on pavement and dirt here in Colorado. Some rock crawlers here run the mud terrains as the lugs last longer on sharp rocks compared to the KO2 all terrains, but I prefer the all terrains.

[rws31]

The plugs were fine for about 4 or 5 months and there was no carbon. Shortly after replacing the vacuum canister a few weeks ago is when it started fouling. It took about a week after the charcoal canister before it started throwing carbon out the tailpipe when idling. The carbon was visible on the sidewalk but not visible in the gas coming out of the exhaust

If your looking for carbon build up on the plugs to see how your fuel ratio is doing, your not looking for the right things.

Search the net, for a competent site not Joe Bob's Youtube sight on spark plugs, and see what your plugs are doing.

Put a new set in and drive it normally for a day or so. Pull them out and look at them. They will tell you what you have going on.

[Dave Jeeper]

I installed a new o2 sensor and the engine is running leaner now and is not throwing codes on the Howell TBI GM computer.


I played with timing, no spark knock at up to 30 degrees btdc (high altitude is 17 +-2) base timing. I have set the base timing to 21.5 btdc.



Power is still poor with or without the new EGR attached to vacuum.


I am suspecting compression issues and will do compression and leak down tests when I have time.

[Dave Jeeper]

I checked engine compression and all is good (tested with cold engine at 60 degrees F, varied between 120 and 130, with one cylinder at 117, taking 10 turns of the engine to pump up to max pressure on each cylinder) . I re-gapped the plugs from .052 down to .040" (I have HEI) and the vehicle is idling and running very smooth with base timing at 20.5 degrees BTDC. No longer getting carbon out of the exhaust after replacing the O2 sensor.



Acceleration up a mild hill is 0 to 55 in about 20 seconds. This is without air conditioning, can't imagine how slow it would be with the AC on. The transmission does not slip at all when accelerating (monitoring the tach). The air intake is functioning correctly and there is a new cat/muffler/tailpipe. The vehicle is running quietly and smoothly now. TBI, HEI, EGR and charcoal canister seem to be functioning correctly now. I do not believe that there are any vacuum leaks at this point.



I reconfirmed that the gearing is 3.31 (3 1/3 turns of the driveshaft per two turns of one wheel with the other wheel on the ground). I have new 31" tires and a 4" lift.


If anyone has any ideas on lack of power I am open to hearing them. I have not checked fuel pressure yet to the TBI, but had cleaned the tank and installed a new pickup about 400 miles ago when I got the vehicle running again.



Not sure why the power is so low, I haven't driven any other SJ's so I can't compare it to other wagoneers. My 1997 XJ is much faster.

[wiley-moeracing]

Compression at 220 per cylinder? more like 120 maybe?

[Dave Jeeper]

Thanks, I edited out the typos on my last post regarding compression numbers.

[wiley-moeracing]

You still should be better than 20 seconds to hit 60? are you getting full throttle on the tbi? Hell a loaded 18 wheeler will do that! 120 psi is a little low but will run ok, you may need to find a good shop/mechanic to help, your missing something somewhere.

[Dave Jeeper]

20 seconds to 55 mph up a slight hill. It seems to have less power in the lower half of second gear. The tranny is not slipping. It is possible that the throttle could open a tiny bit more if the carpet was not in the way. The Howell throttle body might require a little more down travel on the gas pedal to fully open the throttle compared to the original 2150 carb. I will check if there is slack in the cable, perhaps some careful bending can improve throttle opening.



I replaced the single exhaust cat, muffler and tailpipe with oem diameter aftermarket equipment. The cat looked to be free flowing, only a screen in there, no ceramic. Will using a larger diameter or dual exhaust give significant power gains? I also have the passenger thermostatic exhaust valve on the downpipe. Will tying that in the open position help with better power? The valve moves freely by hand and returns to the closed position via the spring with the engine off and when cold.

[Dave Jeeper]

Thanks to wiley-moeracing for solving my power problem!!!


The throttle plates on my Howell throttle body were not opening fully, probably 10 or 12 degrees shy of vertical. The throttle cable from the pedal to the arm on the throttle body was not able to pull far enough. First I tried bending the arm on the gas pedal that pulls on the cable, but this didn't work enough. Then I tried opening up the holes in the support plate for the cable on the engine and moving the cable housing/support further away from the throttle body. It worked, throttle plates fully open.


Much more power and I lowered my timing from 20.5 to 18.5 degrees BTDC (High Altitude spec is 17 or 17.5 +/-2). Engine is now running smooth, idling great and I have more power. I will have to see how it runs with air conditioning in the summer going up the mountains here in Colorado. I don't think that I will need to regear unless I were going to tow a trailer.


The lead foot is now optional, thanks for your help!

[wiley-moeracing]

Good to hear! Sometimes its a little thing that gets missed.

[PlasticBoob]

So what's the 0 to 55 now? 19?


Always good to see people come back and actually post the solution to their issues.