Gearing for someday Jeepspeed XJ

[jlogandro]

I am buliding a 97 XJ with the goal of it being jeepspeed ready in a few years. Until then, it is my daily driver and also will be used for long road trips to wheeling and camping destinations outside of Southern Cal. I am currently running 33s on the stock D35 with 3:55 gearing - I know this package is as bad is it gets. I am trying to decide what axle to replace the rear with; but first must decide the gearing. What do most of you run who use your jeeps for jeepspeed? I am considering 4:56 or 4:88s. I understand that the 4:88s would be better in the dirt. What kind of MPG difference can I expect between the 2 while the jeep is still a daily driver and I have no tow veihicile? I have an extra set of 31 ATs that I have also considered using for round town/commuting to save some $on gas; but I am not sure if I would just shred them up with the 4:88s and still not get good mpg since the enjine would be reving so high.
Thanks!

 

[julio_a]

you can find a later model 8.25 and gear it, or you can go all out and get a 9 inch and 2 sets of third members. one for street and one for trail. if youre going to seriously race it, the 9 would be a better choice too.

 

[tbburg]

I wouldn't worry to much about race gearing right now. For a street/DD on 33"s, go with 4.10s or 4.56s(I'd go 4.56, but that's just me.)

When you go to race it, you're going to be building a D-44, Ford 8.8", or 9" trussing the axle, installing a locker or(more likely out back) a spool, hi-strength axle shafts, and using 4.88s or 5.13s. If you want to get the axle now, the Cherokee -44 or Explorer 8.8 are your options(the 9" is a custom build) If you get the correct 8.8, it'll already have 4.10 gears(and disc brakes), which may affect your decision on what gears to run for now.

 

[xcm]

I love my 4.56/33's/automatic on the street, the same combo, but with 31's was very liveable. Its high in the revs, but nothing crazy, and very driveable. I'd say 4.56 untill you register a 17xx.


if mpg's are that much of a cost concern, you dont wanna get into racing!

 

[tbburg]

...,if mpg's are that much of a cost concern, you dont wanna get into racing!

No kidding! The 7118 truck gets about 6mpg

 

[DieselSJ]

For racing, most teams are running something in the mid-5's, and a couple are running as low as a 6:1. Few teams are running 4.88. With the engine limitations we just don't have enough power to pull a 4.88 gear when racing. We keep going lower and lower, and we keep getting faster and faster.

For the street, either will do fine and you won't really notice a mileage difference between them.

 

[DieselSJ]

No kidding! The 7118 truck gets about 6mpg

That is REALLY good. Our Jeepspeed doesn't even get quite that good.

 

[tbburg]

That is REALLY good. Our Jeepspeed doesn't even get quite that good.

It's all in the superior aerodynamics of the Comanche. :roll:

 

[Johnnie Walker]

An engine swap may assist your need for speed without super low gearing.
Are swap allowed in the Jeepspeed class (not strokers, but other engines)?

 

[tbburg]

An engine swap may assist your need for speed without super low gearing. Are swap allowed in the Jeepspeed class

1700 rules require the stock block. 3700 allows different motors, not sure about different manufacturers. There's at least one 3700 XJ with a 401 V-8 in it.

 

[xcm]

suspension/chassis/drivetrain first. worry about the motor once you get going semi-fast.

he hasnt even built it yet, swapping out the motor at this point would just delay the build.

if hes worried about his mpg, he aint building an all out 37xx truck... he said its for a 'dd' and 'camping' rig

 

[ratboy93]

well he also said he was interested in his rig being a js rig in a couple of years...

is the xj 2 or 4 wheel drive 2.5 or 4.0?

5 speed or auto?

if your going to go js in a couple of years stick with the d35 for now and save your money for a 9" later on when your ready to tear your xj down to nothing and build a js. Now you could get a ford 8.8 if you want to save a lil money now they are nothing like a nine but are still pretty strong.


like diesel said above most js teams are running in the mid 5's i know a guy Rex Lair js 1769?( correct me if im wrong) running a 4 cylinder 5 speed 2 wheel drive with a 6.0 gear out back... and he straight haulsssss

 

[ratboy93]

1700 rules require the stock block. 3700 allows different motors, not sure about different manufacturers. There's at least one 3700 XJ with a 401 V-8 in it.

well thats not entirely true... i believe it can be any motor 2.5 or 4.0 under 4 litres. cause i know a couple guys that either are a full js rig or others being built that run a 2.7 stroker

 

[julio_a]

well thats not entirely true... i believe it can be any motor 2.5 or 4.0 under 4 litres. cause i know a couple guys that either are a full js rig or others being built that run a 2.7 stroker

has to be a motor that came from the factory. and there is a displacement limit for 1700, i dont know it off the top of my head.

 

[ratboy93]

4.1.5 Engine
4.1.5.1 Restricted to original equipment engines supplied to the original Jeep model. Any year model engine is allowed
as long as it was originally available in that specific Jeep model.
4.1.5.2 Maximum engine displacement is 4097cc (250 cu in.) This would allow a 4.0-liter engine to be rebuilt with
.060 oversized pistons with a little extra for honing cleanup. Four cy inder and V6 engines may be bored and/or
stroked to a maximum displacement of the same size.
4.1.5.3 Stock block and cylinder head must be ret ained. It may be bored, ho ned, decked, and otherwise machined as
long as all other rules are adhered to.
4.1.5.4 Stock block, cylinder head(s) and oil pan must be retained. All internal parts are open. No dry sump lubrication
systems, but oil pan may be modified to increase capacity. 2.8 liter V6 engines may be replaced by similar GM crate
motor with iron block and head castings similar to those used in Jeep XJ’s.

 

[julio_a]

4.1.5 Engine
4.1.5.1 Restricted to original equipment engines supplied to the original Jeep model. Any year model engine is allowed
as long as it was originally available in that specific Jeep model.
4.1.5.2 Maximum engine displacement is 4097cc (250 cu in.) This would allow a 4.0-liter engine to be rebuilt with
.060 oversized pistons with a little extra for honing cleanup. Four cy inder and V6 engines may be bored and/or
stroked to a maximum displacement of the same size.
4.1.5.3 Stock block and cylinder head must be ret ained. It may be bored, ho ned, decked, and otherwise machined as
long as all other rules are adhered to.
4.1.5.4 Stock block, cylinder head(s) and oil pan must be retained. All internal parts are open. No dry sump lubrication
systems, but oil pan may be modified to increase capacity. 2.8 liter V6 engines may be replaced by similar GM crate
motor with iron block and head castings similar to those used in Jeep XJ’s.

yep, has to be an engine offered in a jeep cherokee. be it the 4cyl, straight6, or that oddball chevy v6.

 

[dakineJ]

I second what tbburg said.Look for an 8.8 for your DD with 4.10's/disc's,from a 95+ Explorer.Then, when you can,regear to 4.56,as xcm suggested, all the while be thinking about a 9" for racing.

 

[DieselSJ]

i know a guy Rex Lair js 1769?( correct me if im wrong) running a 4 cylinder 5 speed 2 wheel drive with a 6.0 gear out back... and he straight haulsssss

Um, yeah, ok. For the $$ that he has sunk into all the custom internals on that 2.7L stroked 4 cyl, it still can't pull as well as a 4.0. I still can't figure out why someone would give up 78 cubic inches of displacement.

 

[ratboy93]

just for the personal enjoyment you feel when you beat someone with a big bad 4.0...its def worth every penny to guy like me or rex

 

[srimes]

Um, yeah, ok. For the $$ that he has sunk into all the custom internals on that 2.7L stroked 4 cyl, it still can't pull as well as a 4.0. I still can't figure out why someone would give up 78 cubic inches of displacement.

I guessing for the weight. What's the difference, 150 lb?