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How do I pull a grade in this thing?

Y

yossarian19

NAXJA Forum User
Location
Grass Valley, CA
I've got a high flow down pipe & 2.5" cat married to a flowmaster 40 with the stock tail pipe. Also running a K&N cold air intake & upgraded injectors (stock flow, better spray pattern). AW4, 235/75/15 tires & stock 3.55 gearing.
Jeep is dog slow going up the mountains to Lake Tahoe.
Now what?
Will going to a 2.5" cat-back & bolting on a 60 or 62mm throttle body give me what I want - passing power at around 2,000 -3,000 RPM?
Or what about bumping the compression ratio slightly, shaving some off the head or the block & slapping down a .043" head gasket? I don't want to be stuck using race gas but if it gets me the power I want, I don't mind using mid grade or premium
1.7 ratio rocker arms? I hear mixed opinions on these, but mostly "OMG what a great buy"

I've read through dino's site but it looks like most of the upgrades he's done that I haven't add nickel and dime power in the top end. If I'm wrong, somebody tell me: I don't mind plugging away with small upgrades but so far, I haven't seen much result.
Also: I'm not building a stroker. I don't have the space for an engine build & a dead car. Similarly, I'm ruling out engine swaps.
 
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I live here in Colorado (higher elevation). A 4.0L does a pretty good job if it isn't overloaded and geared correctly. Either down shift, or a stroker. Most engine mods do little for the money. I run a 4.7L stroker and love it but remember an XJ isn't light and it will slow down on the hills. The higher you go the less power it will generate.
 
Going from sea level to higher elevation is tough sometimes. Correct me if I'm wrong but some vehicles are tuned differently for higher elevation areas? I haven't done much high elevation driving recently, but my XJ gets up hill decently. Do not be afraid to shift into direct drive and run 4k rpm going up hill. strokedjeep.com bored throttle body is worth the money. higher flow exhaust will help to a point. Too big will counter act it tho.
 
Yeah, I somehow forgot to put it in "3" while climbing.
Some vehicles, including the Jeep, will have a different tune for high altitude driving. A frequent trick the engineers pull is to let the MAP take a barometric pressure reading at the start of each run cycle and use that figure to adjust the EFI. As you gain altitude, though, that tune is less accurate for conditions. Some cars will repeat sample while running, some won't.
Any case, what I'm seeing is "Yeah, exhaust & TB upgrade will help a bit but not a lot. Strokers rock"
Any input on CR games or rockers? Guys are reporting 13 rwhp, but that's on ls1tech.com with 1.85 ratio rockers... Does it logically follow that on our smaller, closer-to-optimized 4.0 engines that I'd see a lot less than 13 rwhp? Or are there details I'm missing?
 
yossarian19 said:
AW4, 235/75/15 tires & stock 3.55 gearing.
Jeep is dog slow going up the mountains to Lake Tahoe.
Now what?
Click to expand...

A set of 4.10 axle gears will make your Jeep perform like a greyhound.
 
Gears or possibly port a head slightly, .043 head gasket and shave the head to bump the compression. Would have more balls, be more efficient and would get better mileage to boot.....if you kept your foot out of it:)

Gears would be your biggest gain, followed by the head and compression bump, cam and then 1.7 roller rockers.
 
desertjr said:
port a head slightly, .043 head gasket and shave the head to bump the compression.
Click to expand...

Would only really make a noticeable difference above 3000rpm. An axle gear swap is by far the better option.
 
Dr. Dyno said:
Would only really make a noticeable difference above 3000rpm. An axle gear swap is by far the better option.
Click to expand...


Hence why I stated gears would be the biggest gain...

And no I think a cam/ported head would make a very noticeable difference around 1500+ pending the cam chosen and how much was done to the head. But mild clean up work will help everywhere, and of course a nice rv style/dual pattern cam would help him out down low & in the mid range where he needs it.
But yes gears would be by far the best & could be cheap pending what he finds.
 
desertjr said:
And no I think a cam/ported head would make a very noticeable difference around 1500+ pending the cam chosen and how much was done to the head. But mild clean up work will help everywhere, and of course a nice rv style/dual pattern cam would help him out down low & in the mid range where he needs it.
Click to expand...

Yup, combining a ported head with an RV style dual pattern cam and a slight bump in CR would certainly make a difference even from low rpm. Add in regeared axles and the Jeep would rip.
 
I thought the 98 camshaft was about as big as a 4.0 could make use of..?

Anyway, I think what I'm deciding is that the money will be better spent elsewhere for me. Just going to cost too much to make a sincere difference in the Jeep's performance, so I'll be leaving it alone except to finish the exhaust in 2.5" cat back & bore my throttle body out to 60mm. Upgrade the electrical system, upgrade headlights, call it a day.

Thanks for the input, though, guys. It's what makes NAXJA my first stop for Jeep info
 
Having driven up to Tahoe many times from the bay area in two different XJ's, I can confirm that it can be a bit of a struggle depending on the speed. My 94 was a 5 speed, 3" lift, and 30" street tires on the stock 3.07 gearing (stripped model so lighter vehicle). Because it was a stick it was much easier to pick the right gear for the speed. This one actually went alright up the mountain even with a roof rack and loaded with camping gear. Not a beast like my WJ (V8), but not bad. My 93 had a 2.5" lift and 31" A/T's with stock 3.55 gears, K&N intake and Dynomax exhaust (fully loaded heavier model). This one was OK for the most part, but definitely felt worse with gear hunting in the auto. And driving up 88 past Kirkwood was terrible in the 93. Windy road with speeds that made 2nd gear a little too low and 3rd too high. Lots of hunting, manual shifting, and RPM's.

Best anwer, gears. Intake, header, exhaust all make minor improvements but not something that I think will solve your issue. I just don't think there is enough power from the 4.0L to accelerate up those grades at that altitude.
 
american_zero said:
Not a beast like my WJ (V8), but not bad...
Best anwer, gears. Intake, header, exhaust all make minor improvements but not something that I think will solve your issue. I just don't think there is enough power from the 4.0L to accelerate up those grades at that altitude.
Click to expand...

The WJ is a thirsty beast and still has a solid front axle, but I've driven a WJ with the 4.7 HO and it was saucy. More comfortable to drive & better amenities than the Xj, too. More cargo space, even!

I keep telling myself If I ever get rid of the XJ it will be for something with IFS & more power, but the WJ is tempting...

And thanks for confirming it isn't just me : the 4.0 is great in low speeds but doesn't have the chutzpah for driving in the mountains.
 
yossarian19 said:
The WJ is a thirsty beast and still has a solid front axle, but I've driven a WJ with the 4.7 HO and it was saucy. More comfortable to drive & better amenities than the Xj, too. More cargo space, even!
Click to expand...

That sums it up pretty nicely. Gas mileage is not a strength, that's for sure!
 
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