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Rolling resistance and driveline efficiency?

I KNEW i recognized that. hahahaha. good stuff :cheers:
 
Hey doesn't the 4.0 get more efficient with the backpressure of a cat inline? That would help you gain a MPG or so.
oh sorry this is about rolling resistance my bad, thought it was just overall efficiency and MPG's
 
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Ty2003K said:
How exactly do better materials and tighter selection tolerances make a bearing smoother? And better lubrications will do nothing for your gas mileage.
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Where do you get off?

out of round, offset material weight, stress fractures, improper casting/cooling times etc etc all lead to excessive bearing wear. In a perfect engineering world no machine would need lubricants, but they're here because we can't manufacture bearings/moving parts to perfect tolerances. A better lubricant makes up for the lack of precision control in surfaces needing that lubricant, ie makes it more efficient. As you increase precision manufacturing on that component, a higher grade lubricant will be needed to increase efficiency, and this cycle will go on until we can make a lubricant 1 micron thick lubricate a bearing with a tolerance of only one micron. See where I'm getting at?

Better lubricants WILL do something for mileage, but it's very, very little... although better lubrication in everything driveline related will eventually add up to say, one mpg?

I say the best combo for an XJ in terms of efficiency would be the 2 door 2.5TD/5spd/231, with a vac disco front axle. CV joints instead of U-joints (on the front axle at least). Next would be the same but 2.5L MPI from 1995 to 1998.

I think I read that the aw4 is about 70% efficient... parasitic driveline loss SUCKS with them.

of course, we could all be REALLY gay and get ourselves a 2wd XJ for an extra 5mpg or so...

Oh, and methinks the best way to improve mileage on a 4.0 is to stroke it, balance it, open up the head, and get a new cam. Stock 4.0's may outlive cockroaches in a nuclear holocost, but they'll always come from factory with insanely huge tolerances and stupid balancing of the crank. Not to mention the HO cam has too much valve overlap, which puts the torque curve right in the WRONG spot for the XJ.

I think the main reason stroking it improves mileage is because of the tighter tolerances associated with an aftermarket rebuild, and that SMART owners break in the engine properly then switch to a high grade synthetic for more efficiency. Top that off with a change in the torque curve and even particularly heavy rigs can get good gas mileage...

I decided today, when choosing between pounding on the new engine and sorting out my wiring harness, that I want to become a mechanical engineer rather than an electrical one...

Oh and correct me if I'm wrong on anything... I'd like to learn from any mistakes!
 
Cherokee's don't get good gas mileage because they're American.


Duh
 
oo7ravisXJ said:
Cherokee's don't get good gas mileage because they're American.


Duh
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Jokes maybe? The XJ is actually french... well half french... just so you know!

... and the only reason we can't get good mileage is because we have ridiculous emissions requirements...

Europe gets to have all their happy turbodiesels with cheaper diesel prices... all because if a vehicle meets MPG requirements they don't have to pass the same emissions requirements... A bluetec(?) jetta supposedly gets 90 something MPG with respectible power ratings on a small four cylinder turbodiesel. I just read that it's being cleared for US emissions, but wont get the same power/MPG ratings... ugh!
 
Mr_Random said:
Oh and correct me if I'm wrong on anything... I'd like to learn from any mistakes!
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not wrong, per se IMO, but here's what i've got.

Better lubricants WILL do something for mileage, but it's very, very little... although better lubrication in everything driveline related will eventually add up to say, one mpg?
Click to expand...
probably less than .5 gpm, if you had the worst stuff on the market and went to the best stuff for everything

I think I read that the aw4 is about 70% efficient... parasitic driveline loss SUCKS with them.
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even more reason to own a manual

Oh, and methinks the best way to improve mileage on a 4.0 is to stroke it, balance it, open up the head, and get a new cam. Stock 4.0's may outlive cockroaches in a nuclear holocost, but they'll always come from factory with insanely huge tolerances and stupid balancing of the crank. Not to mention the HO cam has too much valve overlap, which puts the torque curve right in the WRONG spot for the XJ.

I think the main reason stroking it improves mileage is because of the tighter tolerances associated with an aftermarket rebuild, and that SMART owners break in the engine properly then switch to a high grade synthetic for more efficiency. Top that off with a change in the torque curve and even particularly heavy rigs can get good gas mileage...
Click to expand...
it could also have to do with the fact that the expansion ratio increases with longer stroke, so there's less extra power at the end of a stroke than stock. for normal size engines, there's still quite a bit of pressure in the cylinder when the exhaust valve opens, but having a longer stroke uses up some of that pressure.

I decided today, when choosing between pounding on the new engine and sorting out my wiring harness, that I want to become a mechanical engineer rather than an electrical one...
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haha... just don't design electrical connections. because whoever designs those designs them to break apart when you pull on them. it can make quite the headache.
 
asp387 said:
not wrong, per se IMO, but here's what i've got.

probably less than .5 gpm, if you had the worst stuff on the market and went to the best stuff for everything

even more reason to own a manual

it could also have to do with the fact that the expansion ratio increases with longer stroke, so there's less extra power at the end of a stroke than stock. for normal size engines, there's still quite a bit of pressure in the cylinder when the exhaust valve opens, but having a longer stroke uses up some of that pressure.

haha... just don't design electrical connections. because whoever designs those designs them to break apart when you pull on them. it can make quite the headache.
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I would design them with 12 guage sheet metal surrounding, ugh... twenty-two years of heat and stuff really hate the plastic clips of my harness... that's the main reason why I don't want to deal with TBI shiza... Upgrading to MPI (ugh kinda, but yay at the same time!).

My dad's an electrical contractor, and I have tons of experience through him and electronics classes at school, as well as my own tinkering and internet learnings, but mechanics is SO much less boring! Perhaps the eight hour structured wiring sessions working for my dad on way too many projects is what influenced this... I swear, I've done several thousand cat5 and coaxial terminations, as well as quite a few cat 4, and now getting into cat 6... That's not including the security wiring and related computer systems... then there's the thousands of high voltage outlets... Oh did I mention I'm trying to help you lock the thread too? haha...
 
By 20 or 30 MPG I mean mixed. I get a little over 20 on the highway but in town I get around 16.

And as far as the brilliant individuals tryin to get the thread closed, if you don't like the thread then don't read it, or post in it. It was a question worth asking but if you disagree, then simply leave. There's no need to instigate sh*t just for the sake of causing trouble.
 
PurpleCherokee said:
By 20 or 30 MPG I mean mixed. I get a little over 20 on the highway but in town I get around 16.

And as far as the brilliant individuals tryin to get the thread closed, if you don't like the thread then don't read it, or post in it. It was a question worth asking but if you disagree, then simply leave. There's no need to instigate sh*t just for the sake of causing trouble.
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when the jeep was running great... 20 mpg city, 25 highway... and even then it wasn't running too great. Hopefully the refresh will get it back up there, then I'll see what I can get with 31's too...

oh, and I believe some of the people saying they're helping to close the thread were just mocking the ones that were calling it gay and dumb shit like that. At least that was my intention...
 
besthaticouldo said:
you don't buy a cherokee for gas mileage

plain and simple

im happy when i get 16
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I did. I get twice what my fullsize Jeep got. They're fuel efficient compared to other off road vehicles.
 
IslanderOffRoad said:
I did. I get twice what my fullsize Jeep got. They're fuel efficient compared to other off road vehicles.
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this gets back to trying to polish a piece of crap. it just can't be done.
 
besthaticouldo said:
yes but not compared to most cars...

my jeep gets half what my motor swapped focus got and only 2/3 what my boosted saturn got...
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Hence why I daily drive an 06 Accord that gets 30mpg
 
asp387 said:
this gets back to trying to polish a piece of crap. it just can't be done.
Click to expand...

Yeah. I don't worry about what my XJ gets, because IMO it gets enough to justify me driving it long distance to wheel (i.e. Moab)
 
Mr_Random said:
Jokes maybe? The XJ is actually french... well half french... just so you know!

... and the only reason we can't get good mileage is because we have ridiculous emissions requirements...

Europe gets to have all their happy turbodiesels with cheaper diesel prices... all because if a vehicle meets MPG requirements they don't have to pass the same emissions requirements... A bluetec(?) jetta supposedly gets 90 something MPG with respectible power ratings on a small four cylinder turbodiesel. I just read that it's being cleared for US emissions, but wont get the same power/MPG ratings... ugh!
Click to expand...
I'm not complaining about the 46mpg my Jetta TDI gets, but diesels don't need to be emissions tested anyway! Originally, they have to run clean, but once you buy them you can do whatever you want to them including chips, nozzles, turbos, propane, nitrous, etc and noboy can do anything about it. Theres no "50 state smog legal" parts for diesels because none of the 50 states actually cares to emissions test diesels. Anyway, I do agree that we have much stricter emissions and safety laws here, but if you buy a diesel you can get around those :)

Bluetec is Mercedes, TDI is VAG. The reason diesel is cheaper over there than over here is because they have a different refining process than we do over here. They create more diesel to begin with than we do, so diesel will always be more expensive, not to mention the fact that we process it more to get the ULSD stuff.
 
So immature... can't say I didn't smile myself, though. :D
 
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