mitsubishi diff ratios

[v6triton]

hey guys, new to this site, so hopefully someone out there can help me. i have a 1989 mits triton 4x4 currently running 4.62 diff ratios, i would like to swap them for 4.11, to reduces rev range at 100kmh, any help would be muchly appreciated

[Mr Termite]

What's the question mate? Can you do it? Are the 4.11s a straight fit?

While we're going, I have an 05 GLXR 2.8TD and it has 4.363's.

[v6triton]

sorry, yeah, are there any diff gears that are a straight swap? im currently revving on 2400rpm at 100km/h, and would like to reduce it to 2000-2100rpm at 100km/h. Reason is, cause its running a commodore v6/4spd auto, im not too sure if these engines are designed to rev at this rpm for a long period of time, as i built my ute for long intestate trips

[bakerboy]

sorry, yeah, are there any diff gears that are a straight swap? im currently revving on 2400rpm at 100km/h, and would like to reduce it to 2000-2100rpm at 100km/h. Reason is, cause its running a commodore v6/4spd auto, im not too sure if these engines are designed to rev at this rpm for a long period of time, as i built my ute for long intestate trips

2400@100kmh? thats awesome, mine runs 3100@100kmh, be happy with what ya got hahaha

[Chris_McCartney]

Agree with bakerboy that is awesome, I'm stuck with 5.29 diffs until I find someone breaking a petrol for the 4.88s or whatever they are!! You're spoilt lol

[bakerboy]

5.29's?! where are you located?

[Chris_McCartney]

The northern end of sunny little Ireland (ain't sunny at all!!)

[v6triton]

hey guys, thanks for the replies, if the holden v6 engines were designed to rev at 2400 all day everyday, i wouldnt worry, but im not really sure if its healthy for the engine, i have now fit 33" tyres and its dropped to 2200-2250, compared to the 31" tyres (2400rpm). the last thing i wanna do is replace engine\trans\transfer case, due to high revs, the conversion wasnt as easy as stated by workshop company or conversion manual.

[bakerboy]

damn you chris

v6triton, seriously i think your doing fine, mine does road trips all day long sitting at over 3thousand, apart from drinking the fuel its fine

[v6triton]

hey guys, just put a set of 33" BFGee's, now i sit on 2050-2100rpm, much happier now, just need to change my speedo cable, showing a little less than actual speed, But economy is bloody great, think im averaging roughly 520-550km to a tank, compared to 440-450km

[Chris_McCartney]

Bakerboy why would you want 5.29 if you don't mind me asking?!

[bakerboy]

ive gone from 27"s to 32"s, low range suffers, so rather than crawler gears that only do lowrange, and in between diff ratio change would be better, although id prob go the 4.8's rather than the 5.2's

[Chris_McCartney]

My JTop died and I replaced it with a 2.8 auto.... sitting at 60 or 70 and hitting overdrive is nice, drops it down to 2000rpm... Not sure what gears the 2.8 auto is now!

[tritontray]

hey guys, just put a set of 33" BFGee's, now i sit on 2050-2100rpm, much happier now, just need to change my speedo cable, showing a little less than actual speed, But economy is bloody great, think im averaging roughly 520-550km to a tank, compared to 440-450km

Hey guys. Sorry to high jack a little, but I need to ask some questions about this, as its been raised and I have always had these questions to ask. I now own a Nissan terrano II (could be my problem) 2.7itd but love the Mitsu section as you guys are nicer!.

I don't understand, how adding load (Load=Heavier bigger rubber+increased rolling resistance and circumference+wider tread foot print+more aggressive tread pattern) results in better fuel economy. I realise that larger rolling circumference=lower rpms, but you still have to push it all along with your right foot. And regardless of power and torque out puts load with effectively remove some of that power and torque and will need to be worked harder to maintain forward momentum. In broad terms, is it not the same as hooking a a trailer to a car and towing it? E.G. My 2.7tdi has very similar power and torque figures as the 2.8itd 4m40 I believe which are 92kW @ 3600rpm & Torque 278Nm @ 2000-2000rpm it also has a 2.5inch mandrel bend exhaust and dump, so I get the torque earlier and weighs in at close enough to 2000kg. I have steel rims and 30inch tyres which are one size up from stock which were metric 235/75/15. Ultimately I use more fuel, as I have added load to my car. It cruises at lower RPM, but I have to still keep the foot planted to keep the forward momentum to push the bigger (laughing) rubber and wheels. And I am still yet to return better fuel figures than when it was stock.

For instance if you know the hill on the F3 going north as you leave the Hawkesbury River bridge and head up the first hill towards the mount white speed cameras. It is a 100 zone, dropping from a 110 zone and yes it is a hill, but it is no where near as steep as other sections on the F3. but I struggle, to hold 5th gear up the hill with the bigger rubber, and better torque availability due to the exhaust. So I need to drop the right foot in more to keep it all moving (More diesel=more power if it can take it), it can hold it but it is struggling, so I change down a gear and instead of using right foot to keep it all moving, I am now dealing with a high revving engine sucking same if not more fuel. So once again I still can't see how a vehicle with stock gearing and bigger tyres can return better fuel economy even on flat ground with a high torque and power figures.

The other thing is that manufcturers seem to offer small wheel and tyre packages on lower spec models compared to larger tyre and wheel packages on an up spec model. How can vehicle performance be acurately tested when the same engine is used in both, and how can they produce fuel economy figures when the one with smaler tyres would work easy rpms round town, but high rpms on hwy, and the one with larger tyres will work harder around town to get it all moving and then lower rpm's on hwy but it still all has to be propelled forward.

I once read a write up when nissan bought the sylvia out to OZ. the writer is the only person I have read that picked up the engines were the samme in the benign lower spec dressed up model, the wheel and tyres were the same between upper and lower spec but the fact that the 'so called' sports model was slower because it was carrying more weight due to being dressed up with body kit etc......So I guess after getting all of that off my chest, is it all a false economy..........pardon the pun. Cheers guys.

[57oky]

i would have to agree tritontray, when I put my bigger rubber on my fuel economy went out the window along with my torque. I lost a full 100km per tank and and everything it had down low. The only thing I picked up was off road traction....

[-Scott-]

This really is a complex issue, with lots of factors to consider, but you're right - it's difficult to improve economy by swapping to taller tyres.

I don't know how true it is, but I've read that an engine operates most efficiently at its torque peak. So, if you take a torquey motor (i.e. turbo diesel) with a comparatively low peak torque (i.e. 2000 rpm) and drive along the highway at 100km/h you'll use a certain amount of fuel. If larger tyres reduce the engine rpm, but bring it closer to the peak torque, then the improvement in efficiency may be more than enough to counter the increased load of the larger wheels and tyres (all other things being equal).

Driving style can also play a part in it. Pre-tyre change, the driver might simply floor the throttle and let the engine lug up the hill in 5th, burning as much fuel as the injectors pump in. With the taller tyres, if the vehicle is unable to maintain the same speed (because it falls off the torque curve sooner?) then changing down will increase the revs, but may allow the engine to operate in a more efficient rev range, with reduced throttle. Maybe?

Personally, I've never been a big fan of leaving it in top gear and letting it lug away at low revs. I'll often drop back to 4th and maintain speed at higher revs, but less throttle.

Personally, mine sits about 130mm higher than stock, so it's a lot less aerodynamic. I know why it sucks through fuel.

[Chris_McCartney]

Certainly once the wheel is rolling then kinetic energy lends a hand? I would imagine the difference in MPG is under acceleration, uphill, and getting up to the engines peak torque figure? The wider wheels do add more resistance, especially mud tyres (they killed my fuel economy), but when you're sitting at the engines peak torque around 100km/h then the wheels will have picked up a good bit of energy and gravity would be aiding the MPG.... so I guess my point is that the bigger wheels would affect MPG more under starting and stopping, ie. city driving? Once you're on the motorway/freeway (not sure what theyre called in Australia) the wheels pick up a lot of kinetic energy and won't be putting as much strain on the engine?! Land Rovers are fitted with narrow tyres, much narrower than Terranos and Pajeros, but there are tall narrow options available, such as 255/85/16 - this is 255mm wide but almost 33" tall. If you go Land Rover tyre sizes then there are tires around 200mm wide yet reasonably tall. My Pajero is used on tarmac so the mud tyres are unnecessary but look damn cool. MPG can be affected by the underside of the car too, thats why the bumpers are much deeper on new Pajeros, them big solid axles on Toyotas aint too aerodynamic and just add to the drag!! (sorry I cant remember if Terrano is IFS or solid axle).

If you want to save MPG then stay away from aggressive offroad tyres unless you need then, my fuel tank drops ridiculously fast, especially in urban driving. Last week I used £70 (over $100 maybe?) on fuel just cruising and showing off my new Pajero, and I never left the town I live in!!

You never mentioned what type of tyres you use tritontray? Radial, all terrain, mud terrain? Radial would expect 26-30mpg average on most 4x4s, all terrain drop down to around 20-24mpg, and mudders.... way below 20mpg average!!

[Ian Sharpe]

I don't know how true it is, but I've read that an engine operates most efficiently at its torque peak. So, if you take a torquey motor (i.e. turbo diesel) with a comparatively low peak torque (i.e. 2000 rpm) and drive along the highway at 100km/h you'll use a certain amount of fuel. .

Using that formula the petrols achieve their max torque much higher, eg the 3.5l max torque is 303nm @ 3400 revs.
I wouldnt like to be driving around all day at those revs, would chew the juice I would imagine.

Interesting though that my NL with 4.636 gets much better economy than the NP with 4.30'. The NP is a tad heavier though, but maybe the 3.5l motor is a bit happier in higher rev ranges?

[v6triton]

hey guys, i understand to turn a bigger tyre requires more throttle to keep the momentum but please understand a commodore/buick engine is more economical at 1800-2000rpm. If a commodore with a 3.08 diff ratio is sitting on 2400-2500rpm it will be travelling at roughly 100-115kmh, now with my 31's i was revving at 2400-2500rpm, which u could actually see the fuel guage drop, since i put the 33's on it has dropped to 2000-2050rpm and now i am getting 13l/100km compared to 14.7/100km. My ute doesnt drop gears up hills, doesnt require 'heaps' more throttle to overtake cars as it got heaps more power from factory. If i can sit under 2000rpm, whether it be all day driving or 4x4ing, fuel gauge wont move.

[tritontray]

"You never mentioned what type of tyres you use tritontray? Radial, all terrain, mud terrain? Radial would expect 26-30mpg average on most 4x4s, all terrain drop down to around 20-24mpg, and mudders.... way below 20mpg average!!"

I have Coopers ST LT tyres in 30 inch. I realise all the factors in why fuel consumption goes up. My original post was about trying to understand how fuel consumtion can get more economical by adding bigger rubber (load) to a car regardless of power out puts. Any load however should, to maybe a very minor degree or large degree depending on the load should lessen the ability of the vehicle to operate as economically as it should and certainly not get better fuel consumption, even regardless of power out puts. At work I drive HR trucks with detroit diesels with out puts of about 530kw and over 2395nm in torque. They run massive rubber of Michelin 24R21 on 18 x 21 inch steel rims (they are 4x4's diff locked etc weighing 33t. if we made the rubber even bigger which they can easily push around they would return worse fuel economy and I am satisfied whether it is a truck or car or 4x4 that that fact will not change.

If you are talking about cruising on hwy's being efficient as well, they amy well be but there is not one flat nor straight road in NSW let alone the country (don't under estimate how much extra it takes to drive your car around a corner with the wheels turned, compared to straight driving), which requires throttle changes constantly. Even a 2-3% incline will require more throttle imput regardless of torque. If it were as easy as fitting bigger rubber for fuel economy, then every person who communtes to work on a freeway everyday with none to little city driving should all fit 35's. I am being a bit smart here, but not trying to be rude I just cannot see how it is possible to reduce your fuel consumption by adding load to a vehicle. Cheers again.

[v6triton]

with my original set up worn out 2.6cyl/5 speed manual, if i had put 33's alll terrains on that, i would agree that i'd be using more fuel to turn the tyre, now with the v6 conversion, my torque is almost triple than standard so therefore turning the 33' tyres is like my 2.6cyl turning a 28' tyre. With the set up i have now i have had a set of 31" all terrains and a set of 31" mud terrains and with both tyres i was averaging 440-450km to a tank, and speedo was spot on as i compared it with 2 navigation systems, now with the 33" tyres, every time i fill up i average 500km to a tank, but keep in mind my speedo show less than actual travelling speed (i.e 95km/h on my speedo is actually 100km/h), If my speedo is out would my trip computer be out too???? would i be doing more than the 500km my trip computer shows? Im not trying to argue this point with anyone, ive had these 33's on for almost 4 weeks and got 500km everytime i fill up, so its not a one off thing. anything below 100km/h im well under 2000rpm, car doesnt struggle to keep speed, climb hills in top gear, overtake cars, it drives exactly like a commodore.

[NJV6]

Personally, mine sits about 130mm higher than stock, so it's a lot less aerodynamic. I know why it sucks through fuel.

Therein lies your problem Scott and some others on the board may learn from what your about to read.

You should have just raised the rear and kept the front the same or meet half way and just have 50mm at the front. This means it is now similar to driving down a hill. You will find your fuel use drop and throttle response possibly better than standard. Too many people set them up tall and level then put their camping gear in the back and are permanently driving uphill! So easy to fix.

Glen

[-Scott-]

Personally, mine sits about 130mm higher than stock, so it's a lot less aerodynamic. I know why it sucks through fuel.

Therein lies your problem Scott and some others on the board may learn from what your about to read.

You should have just raised the rear and kept the front the same or meet half way and just have 50mm at the front. This means it is now similar to driving down a hill. You will find your fuel use drop and throttle response possibly better than standard. Too many people set them up tall and level then put their camping gear in the back and are permanently driving uphill! So easy to fix.

Glen

D'oh! I feel so stupid!

But if I go and lower the front I'll need to get the wheel alignment done again. Can I just go back to 31s on the front?

[pjb]

Just mount some lead weights up under the front bumper. Should bring it down 10 - 20 mm.

[NJV6]

Yea 31's should be fine Scott, smaller the better really. And the lead weights thing - well that will help on two counts, the downhill effect and also the more weight effect meaning the car will steam over hills now due to it being like a big flywheel.

[schweps]

Hi,
I think you should calculate the real km during your trip by multiplying wheel diameter ratios with the value you read on your trip computer. Because, as far as i know the rpm is based on the trip calculation.
33/31=1,0645
1,0645x500=532km the real distance that your vehicle ran.

With the set up i have now i have had a set of 31" all terrains and a set of 31" mud terrains and with both tyres i was averaging 440-450km to a tank, and speedo was spot on as i compared it with 2 navigation systems, now with the 33" tyres, every time i fill up i average 500km to a tank, but keep in mind my speedo show less than actual travelling speed (i.e 95km/h on my speedo is actually 100km/h), If my speedo is out would my trip computer be out too???? would i be doing more than the 500km my trip computer shows? Im not trying to argue this point with anyone, ive had these 33's on for almost 4 weeks and got 500km everytime i fill up, so its not a one off thing. anything below 100km/h im well under 2000rpm, car doesnt struggle to keep speed, climb hills in top gear, overtake cars, it drives exactly like a commodore.

[v6triton]

hey guys, its been a while since ive posted my fuel consumption issues, so i thought i'd try and prove myself wrong. I drained my fuel tank completly and filled the tank to the brim and it took 66 litres, i drove 213km's and used just over 19ltrs of fuel, still runnung my 33' tyres and 4.62 diff ratio. My original 4cyl/5spd never came close to this. Could my TomTom be wrong or the program Whereis.Com be wrong???