2k rpm @ 60mph on 31's?

HenryKrinkle · Aug 19, 2009

Just put 31" BFG's on my otherwise stock 88. Now I'm running at 2 thou just to get up to 60mph. Will running at 2 grand for hours damage anything? I'd rather be at 1200-1500ish. Can anyone explain what would need to be done to which gears to get back to normal? I have a stock rear axle (not the d44) and have heard that building them up is a waste because they are weak.
This will be more of a expedition-style traveling truck, and will not see too much abuse or rocks, etc. Is this the point where I get a locker + gears to match? Oh yeah, I also just got all new brakes on the rear....

I'm planning ~3.5" of lift at some point. Also am broke...What are my options?

Any tips or advice would be great.

ROBZ95Xj · Aug 19, 2009

you will be fine at 2k, heck it will live at 3k all day long on the highway

jeeperjohn · Aug 19, 2009

The 4.0 is actually most efficient at 3-4K.

Baja_XJ · Aug 20, 2009

2250-3000 is what ive always heard, 35s, 4:88s and a 5 speed and I get 14 city and 18 highway. Thats running 2750 @ 65, 2500 @ 60, 2250 @ 55, on a motor with 215k on it

ktm racer 419 · Aug 20, 2009

i run anywhere from 2700-3000 on the highway for hours at a time.

BUT

when upgrading to a larger tire size you should be running lower rpms than before.

what did you run on stock tires at the same speed?

XJEEPER · Aug 20, 2009

What Baja said......

Bigger tires are heavier than stock tires and have more rolling resistance than stock, so there is more friction/drag on the motor.

If you're running 31's, I'm going to assume a lift in involved, which also creates more wind resistance, which also creates more drag.

Add some armor and you add more drag on the drivetrain.

It all adds up and no gearing chart takes these variable into account.

A stock XJ with a 5 speed will have 3:08 gears, an auto will have 3.55's. There may be a few anomolies, but this is pretty much the standard issue gearing.

4:10's work pretty good with 31's and a 5 speed, but an auto tranny rig will like 4:56's better.

Target cruising speed of 65-70 mph should be in the 2500-2900 range to get the best mileage, based on my experience with 3 XJ's, a variety of lifts, different tire, wheel combo's and 13 years of ignoring gearing charts and doing it right. I drive mine daily on the freeway with 33's and 4:88s and an auto and average 18mpg freeway. 145K miles on a 2000XJ

Hope this helps.

chpmnsws6 · Aug 20, 2009

jeeperjohn said:
The 4.0 is actually most efficient at 3-4K.

More like 2100-2500rpm

ROBZ95Xj · Aug 20, 2009

my current setup is 3.55 gear and 33's with a aw4, i never use drive, just leave it in 3, doin 55 i get 17-18mpg's and 65 i get 15-16, an thats with GPS

chpmnsws6 · Aug 20, 2009

XJEEPER said:
What Baja said......

Bigger tires are heavier than stock tires and have more rolling resistance than stock, so there is more friction/drag on the motor.

If you're running 31's, I'm going to assume a lift in involved, which also creates more wind resistance, which also creates more drag.

Add some armor and you add more drag on the drivetrain.

It all adds up and no gearing chart takes these variable into account.

A stock XJ with a 5 speed will have 3:08 gears, an auto will have 3.55's. There may be a few anomolies, but this is pretty much the standard issue gearing.

4:10's work pretty good with 31's and a 5 speed, but an auto tranny rig will like 4:56's better.

Target cruising speed of 65-70 mph should be in the 2500-2900 range to get the best mileage, based on my experience with 3 XJ's, a variety of lifts, different tire, wheel combo's and 13 years of ignoring gearing charts and doing it right. I drive mine daily on the freeway with 33's and 4:88s and an auto and average 18mpg freeway. 145K miles on a 2000XJ

Hope this helps.

I was actually pulling better mpg right at 2100-2200rpm, but then again, mine seems to be choked up.

CanMan · Aug 20, 2009

HenryKrinkle said:
I'd rather be at 1200-1500ish..

Thats terrible RPM's on almost any engine for hwy. crusing speeds. You'd rather not be.

4.0 should(needs) to be above 2200(IMO) on the freeway for most effectiveness and least 'drag/lugging' on the engine. Its an undersquare engine, and doesnt mind the higher RPM's. Ive ran mine at 2800 for hours(5+), with no overheating, noises, or ill effects.

winkosmosis · Aug 20, 2009

Bigger tires = lower rpm.

But you should remember that the indicated speed is lower than actual. If it says 60mph, you're going more like 56 or 57

JOSEJALAPENO · Aug 20, 2009

I am running a 4.0 with a auto trans, I have 4.88's & 35's. I run 2500-2700rpm on the freeway. I have good power on the freeway to pull hills.

beakie · Aug 20, 2009

keep in mind unless your getting the speed from a GPS or you've changed your speedo gear... those speeds are a little off.

HenryKrinkle · Aug 20, 2009

CanMan said:
Thats terrible RPM's on almost any engine for hwy. crusing speeds. You'd rather not be.

4.0 should(needs) to be above 2200(IMO) on the freeway for most effectiveness and least 'drag/lugging' on the engine. Its an undersquare engine, and doesnt mind the higher RPM's. Ive ran mine at 2800 for hours(5+), with no overheating, noises, or ill effects.

I forgot to mention I have a bit of a manifold leak. This may make the 2k+ rpm's seem more violent than they really are. That is good news though about 2k-2.5k being the target zone.

Thankya

ktm racer 419 · Aug 21, 2009

i forget what rpms i run but at 60-65 mph i have had anywhere between 18-22 mpg

if i run 75-80 i get around 13-14

5.38's and 36's with an aw4

gps

2k rpm @ 60mph on 31's?

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