Xj mpg

[Sobek]

Originally Posted by alexbrown64

I dont know of anyone who has done the transmission swap. The AW4 has a pretty high overdrive. Where do you believe the problem lays?

I always felt like the 4.0 was revving a little too hard at higher speeds, like say 100kph. I know it's a straight 6 and probably has a specific torque curve that demands this (you're probably starting to see how little I know about these things!) but I always felt like getting those high speed cruising rpm's down further would net some good benefits. It certainly feels like it has the torque for it. Or is this simply something a diff change would be more suited to managing? My bmw has a V8 with a 5 speed auto and a 3,23 diff and the overdrive on that at 100kph has you cruising along at about 1700rpm or so... you have piss all power but it's enough to cruise along and the economy improves dramatically in overdrive.

I'm just spitballing completely uneducated ideas here based on my limited knowledge. Always nice to learn

[awg]

Originally Posted by Sobek

I always felt like the 4.0 was revving a little too hard at higher speeds, like say 100kph.
I'm just spitballing completely uneducated ideas here based on my limited knowledge. Always nice to learn

my near stock sits at ~2000rpm at 100km, I cannot see sufficient reason why one would want to drop that down, it isnt noisy, and the cost of doing so would never be paid back

mine get 16L/100, a lot of short trips.

On my Jag 420G with (Jag 4.2 XJ) motor 3speed auto and 3.54, its about 3200rpm at 100, that IS noisy, and I am hoping to place an Aisin-Warner 4 speed (from a Toyota or Volvo) in there eventually

[Richard buttocks]

Originally Posted by Sobek

I always felt like my XJ just needed one more gear, specially at highway speeds. Does a manual swap make any difference? Is there a 5 speed auto swap for XJ's? I know nothing about transmissions for these cars but always thought there must be room for improvement there.

There is a 5 speed that would possibly work

Unfortunately getting something to control the shifting isnt available. At all.

[alexbrown64]

Originally Posted by Sobek

I always felt like the 4.0 was revving a little too hard at higher speeds, like say 100kph. I know it's a straight 6 and probably has a specific torque curve that demands this (you're probably starting to see how little I know about these things!) but I always felt like getting those high speed cruising rpm's down further would net some good benefits. It certainly feels like it has the torque for it. Or is this simply something a diff change would be more suited to managing? My bmw has a V8 with a 5 speed auto and a 3,23 diff and the overdrive on that at 100kph has you cruising along at about 1700rpm or so... you have piss all power but it's enough to cruise along and the economy improves dramatically in overdrive.

I'm just spitballing completely uneducated ideas here based on my limited knowledge. Always nice to learn

Easiest way to bring the rpm down at cruising speed is to fit larger tyres. Put a set of 31" tyres on and it will drop your rpm right down at 100 kph

[rainman]

wrong place.

[jaffazoom]

I can average 11.5/100 going easy. stock wheels at the moment and 2 inch's of lift.
Best I have gotten is 620km's from a tank full doing about 10km's on the fuel light. This is driving 3 hrs to brisbane the first 100km's is a little hilly after that its highway running also included about 80kms of brisbane peak hour plus the drive back.

my cherokee has done 250.000klm's and has never had the injectors done and is still on the original factory exhaust system. probably needs spark plugs too.

The best bang for buck for saving fuel is lifting your right foot, driving style will net you the best gains.

[Sobek]

Originally Posted by jaffazoom

I can average 11.5/100 going easy. stock wheels at the moment and 2 inch's of lift.
Best I have gotten is 620km's from a tank full doing about 10km's on the fuel light. This is driving 3 hrs to brisbane the first 100km's is a little hilly after that its highway running also included about 80kms of brisbane peak hour plus the drive back.

my cherokee has done 250.000klm's and has never had the injectors done and is still on the original factory exhaust system. probably needs spark plugs too.

The best bang for buck for saving fuel is lifting your right foot, driving style will net you the best gains.

That's pretty amazing in my books... Even since brand new (we've had our XJ since 95) we've never been able to push more than about 430km out of a full tank even with straight highway driving and no aircon / no overtaking. With a mix of highway and local driving, I'm averaging maybe 350km out of a tank, it's pretty sad. And many times I've run it to where the needle won't even pop over the empty mark when pulling up to a stop 620km though... Love it.

When I was younger I was always reading online that it was lots of highway driving that kills these motors early, and I just always assumed it was just from revving its nuts off for prolonged periods. Or was that just naysayers being vocal?

I'm always surprised when I read how little room there is for improvement on mileage with these cars, I don't know why but I always used to think there must be some major gains waiting to be had!