Rally mods

[hubs97xj]

There are some variations (special packages, options), but for the most part, 3.07 for a 4.0/5 speed, 3.55 for 4.0/AW4, and I believe the 4cyl/AW4 got 4.10. I think 3.73 was available with the tow package for some years, but the last two seem to have been, at least here, very uncommon.

 

[XJLI]

you wont have any more power at 5500 then you would at 4000.

 

[WAM174]

Odd ball idea, but have you considered a 4-cyl XJ? Sounds like you're going for all-out handling. The only major down-side of the 4.0 is it's weight. They weigh more then most V-8s, and worse yet, because of the length of the motor, a big part of that weight is ahead of the front axle.

Build up a 2.5, bump the compression, more aggressive cam, bigger TB, injectors, a decent exhaust,... probably can't get up to the 177- to 196HP the various 4.0s put out without blowing serious coin, but 160 is probably doable, and 160 HP with a couple hundred pounds cut off the nose might be quicker on a tight course.

Whatever you decide on, look for a NP-242 select-trac transfer case. The full-time 4wd system with the center differential should handle better then the part-time system.

Interesting thought. But kinda risky since the only reason I got interested in racing an XJ was I saw one do well. If I get something seriously different and don't do well, I won't know if it's me or the car.

But you're right...it's not so much about power. Some of the fastest rallyX cars are the Sube 2.5RS normally aspirated. They have just a fraction the power of a new STi and often beat them.

hubs97xj: thanks for the ratios. Do you also know 1st & 2nd gear tranny ratios?

XJLI: It's got nothing to do with making power at high rpm. It's about not having to shift before the next corner. So what I'm asking is how high can I turn the engine in trying to avoid an upshift. Because I'll just have to downshift again at the next corner. Shifts are time-wasters in competition.

 

[tbburg]

You can run a 4.0 up to 5k, not a problem. What he was getting at is the power drops off above 4k. The 4.0 has a lot of grunt down low, but that's what it's tuned for.

and,
trans data:
http://www.naxja.org/forum/showthread.php?t=101120
axle data(and gear ratios):
http://www.naxja.org/forum/showthread.php?t=101249
Basic power upgrades
http://www.naxja.org/forum/showthread.php?t=101112
all from the FAQs:
http://www.naxja.org/forum/forumdisplay.php?f=165&order=desc

Hope that helps.

 

[WAM174]

Perfect, thanks.

So doing the math, I can hit 54mph with a 91+ 5-speed in 2nd gear on 26" tires and an optimum 60 mph if I use 30" tires.

But the automatic will leave me half way between 1st and 2nd for most events.

Exactly the info I was looking for. Thanx again, Bill

 

[kastein]

4.10s came in 4 cylinder gas 5 speed manual xjs. 4.56s came in some very rare packages, like the renix 4cyl/gas/aw4 and apparently the 84-?? 4cyl autos as well, not sure on that one.

For 1 inch drop you could try lift springs combined with sua. Not sure how tall the lift springs would need to be but you can run the numbers easy enough.

Also, for ease of computation, check out grimmjeeper's motor/tranny/tc/diff gear/tire size calculator. It does some pretty neat stuff.

 

[WAM174]

Hmmm. A 4.0 Automatic would gear out just fine with transplanted 4.10's. Would it be a straight forward ring & pinion swap, or are there any housing differences?

A quick search on your classifieds didn't get any hits on 4.10. Not too common as used parts?

 

[kastein]

They're not very common at all in this neck of the woods. Yeah it'll be a straight swap (and shim reset of course) as long as the donor and your xj have the same axles.

 

[Brown Dog]

You guys have been doing fine. I needed to know if certain years/models were a better choice than others. And the tips on motor and transmission mounts are spot on -- that's exactly the type of failures typical in RallyX. Many a car has gone home with the engine held in with ratchet straps.

Ratchet strap engine cradles are exactly why we started to make brackets! We've made a couple engine mount systems that drop the motor 3/4 to an inch, sometimes more. As heavy as the 4.0L engine is, I'd think the lower COG would help. Don't know about the rules, though .... PM or call if you're interested. RallyX sounds cool!

 

[WAM174]

Not many rules in modified class. Your lowering mounts would be fine. But lowering the engine will of course lower the pan. Isn't axle contact with the pan the limiting factor in lowering the front suspension? Seems like one of the threads linked above showed a 2wd beam axle shaved to half height in order to get maximum lowering for that autocross challenge XJ. Of course I won't be going (and can't go) anywhere near that low so maybe pan interference won't be an issue.

 

[Goatman]

According to Grimm's gear ratio calculator a 30" tire (29" actual) would give you these speeds in 2nd gear with an AW4 auto. This what you were talking about, being able to run only 2nd gear and avoid shifting.

2000 rpm 25 mph
3500 rpm 43 mph
5000 rpm 62 mph

http://www.grimmjeeper.com/gears.html

A 26" tire and 4.10's would give you exactly the same rpm/mph.

Unfortunately, the AW4 in an XJ does not have a way to hold 2nd gear, so you'll have to consider one of the shifting kits that allows you to manually select and hold a gear.

One nice thing about the 4.0L motor is that it has a very wide power band and pulls pretty strong though a wide rpm range. One earlier comment about it not pulling hard past 4000 rpm must come from someone with an older worn out motor, they pull strong from 2500 to 5200 rpm (rpm limited) but seem to pull strongest from 3000-4500 rpm.


Interestingly, top speed in low range at 5000 rpm is 60 mph with 29" tires (30x9.50 15 size) and stock 3.55 gear ratio.

BTW, this looks like fun.

 

[kastein]

If you get a 96 or earlier, you can do a shift kit easily without even setting off the check engine light. Buy whatever shifter you want or a couple toggle/rotary switches and wire it up! The aw4 is dirt simple. In fact if you only ever want first and second, put one of the solenoids on a toggle switch (forget which, easy to find an aw4 gear shift table though) and drop it in 1-2, flip the switch to select 1st or 2nd.

 

[Goatman]

I use the Compu-shift on my buggy to hold 2nd, which works great for me since it will still downshift to 1st if you give it heavy throttle and you're going slow enough to use 1st. I think Bill is trying to avoid shifting at all and holding it in 2nd, so a toggle shift on the 2nd solenoid would work well.

Or, get one of these which are supposed to work pretty well:

http://radesignsproducts.com/default.aspx

 

[WAM174]

According to Grimm's gear ratio calculator a 30" tire (29" actual) would give you these speeds in 2nd gear with an AW4 auto. This what you were talking about, being able to run only 2nd gear and avoid shifting.

2000 rpm 25 mph
3500 rpm 43 mph
5000 rpm 62 mph

Now Goatman...that's interesting. It doesn't agree with what I calculated and might change how I gear this thing.

I don't use other peoples calculators -- I just do the math. Here it is:

V = rpm x dia / (336.1 x G x g) G is axle ratio, g is tranny ratio

So V = 5000 x 29 / (336.1 x 3.55 x 1.53) = 79 mph, not 62.... Bummer.

Are my axle and 2nd-gear ratios right?


Here's why I thought I needed 4.56's:

V = 5000 x 29 / (336.1 x 4.56 x 1.53) = 61.8 Perfect.

If anybody knows where I'm going wrong, don't be shy.

-- Bill

 

[WAM174]

I use the Compu-shift on my buggy to hold 2nd, which works great for me since it will still downshift to 1st if you give it heavy throttle and you're going slow enough to use 1st. I think Bill is trying to avoid shifting at all and holding it in 2nd, so a toggle shift on the 2nd solenoid would work well.

Or, get one of these which are supposed to work pretty well:

http://radesignsproducts.com/default.aspx

My preference on shifting is to launch in 1st, short shift to 2nd and never touch it again. I don't want it to downshift for me. On rare occasion I may want to drop it back to first for a hairpin, but that's not common.

At this point I'm still assuming 4.56 gears and hopefully I can dig out of some pretty tight corners still in second.

-- Bill

 

[WAM174]

If you get a 96 or earlier, you can do a shift kit easily without even setting off the check engine light. Buy whatever shifter you want or a couple toggle/rotary switches and wire it up! The aw4 is dirt simple. In fact if you only ever want first and second, put one of the solenoids on a toggle switch (forget which, easy to find an aw4 gear shift table though) and drop it in 1-2, flip the switch to select 1st or 2nd.

But I just bought a 98 so have to screw with OBD2. Some people say you can do that mod anyway and just live with the check engine light. Others say you can damage something if you try that. I'll do some more reading. There should be no need to reinvent this wheel.

 

[kastein]

If you don't care about the check engine light you can simply ignore it. No worries there, I built a transmission controller I was testing and managed to fool the tcu into passing the solenoid electrical tests but it still fails for solenoid function. Check engine light comes on but everything works fine.

 

[WAM174]

So with my cheapie code reader I can reset the light before going into smog test. I guess the only problem is with the light always on, you might not know when something more critical actually does go wrong. Every so often I can check codes. I can live with that. So do I get to those wires under the dash or down at the transmission? And anyone know the color code? The FSM indicates the two solenoids may be white and orange/white. If nobody knows for sure, I'll figure it out.

 

[Goatman]

BTW, my speed and rpm calcs were for a 4.56 ratio, which we talked about, but I don't think I mentioned that in my post.

I think the check engine light will only come on if you are manually shifting the trans, if all switches are off and the trans is shifting itself there shouldn't be a CEL.

 

[kastein]

You can also get the Montana Fab controller, which allows you to switch between 1/2 on late-model XJs with no CEL.

If it's just gonna be a rally rig and not street driven, though, I would just ignore the CEL unless you really don't like to see it on. I prefer to keep the CEL inactive so I can tell if the ECU is actually trying to tell me something instead of just complaining about the same old problem... and maybe something else as well.