1999,105Landcruiser,petrol,gearbox ratio change ???

Submitted: Monday, Apr 02, 2012 at 19:27
ThreadID: 92970 Views:2753 Replies:7 FollowUps:13
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Hi Gang, I would like to change my gearbox ratio so when I'm cruising at 100kph, I'm sitting at lower rpms, and hopefully get better fuel consumtion... Has anyone done this ? Or heard of this being done ? I'm in Melb. I'm very happy with my vehicle, just trying to achieve better fuel consumption on long trips... Thank you..
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Reply By: Member - Craig F (WA) - Monday, Apr 02, 2012 at 19:44

Monday, Apr 02, 2012 at 19:44
I have a hilux and have increased my RPM and gained economy.

As I had fitted bigger tyres my motor was labouring at 100kmh after changing my ratios I am now 250 rpm higher at 100 and about 1.2 ltr per 100 better off.

Craig
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Follow Up By: GET ON ! - Monday, Apr 02, 2012 at 20:31

Monday, Apr 02, 2012 at 20:31
Hi Craig, which ratios did you change ?
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Follow Up By: Member - Craig F (WA) - Monday, Apr 02, 2012 at 21:04

Monday, Apr 02, 2012 at 21:04
I changed the diffs.

I bought the motor back to its normal revs for 100kmh.
Also fitted a better air filter and exhuast that helped improve economy.

CF
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Reply By: Dave(NSW) - Monday, Apr 02, 2012 at 20:02

Monday, Apr 02, 2012 at 20:02
you need to let people know the vehicle set up, like tyre size and mods to the engine if any. Usually car makers have the ratios already worked out for best economy and power on standard vehicles.
cheers Dave.
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Follow Up By: Dave(NSW) - Monday, Apr 02, 2012 at 20:08

Monday, Apr 02, 2012 at 20:08
Forgot to say it's the Diff ratios you would have to change not the gearbox.
cheers Dave.
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Follow Up By: GET ON ! - Monday, Apr 02, 2012 at 20:30

Monday, Apr 02, 2012 at 20:30
Hi Dave, I have a supercharged 4.5 petrol manual with 265/75 r16 bfg all terrains, 3 inch lift,roof rack,bull bar,winch,rear wheel carrier and lots of other goodies. Terrain Tamer told me they modify the 80 series gearbox to lower rpms in 5th gear. However they don't have a kit for my model. cheers
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Follow Up By: Dave(NSW) - Monday, Apr 02, 2012 at 21:17

Monday, Apr 02, 2012 at 21:17
Sounds like for your set up you need to change the 5th gear, try on here http://www.lcool.org/technical/technical.html they have heaps of info on your car.
Cheers Dave.
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Reply By: pop2jocem - Monday, Apr 02, 2012 at 20:46

Monday, Apr 02, 2012 at 20:46
You can actually modify the gearbox or differential ratios to lower the engine RPM for a given road speed. Don't forget if you choose to change diff ratios you have 2 diffs to do...lol. Also as others have said, you may actually increase your fuel consumption by making the engine work at a lower RPM than it's optimum. Have you looked at a free flowing exhaust and a set of extractors and maybe a so called"chip" fitted to the engine management system. Probably a lot cheaper and more likely to achieve better lt/klm fuel usage and better performance as well.


Cheers
Pop
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Reply By: Ozhumvee - Monday, Apr 02, 2012 at 21:16

Monday, Apr 02, 2012 at 21:16
Wow a petrol 4.5 liked fuel, a supercharged one must really drink it!
Seriously though for best economy you need to have the engine at is optimum RPM which is usually the point on the power versus torque graph where they intersect. There is usually some leeway but most of the time that is the most economical point.
Aggressive tyres, roofracks, trailers and just sheer weight all affect economy to a certain extent, sometimes lifting the foot is the only way to improve it.
Peter
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Follow Up By: GET ON ! - Monday, Apr 02, 2012 at 22:13

Monday, Apr 02, 2012 at 22:13
Hi Ozhumvee, I've owned a standard 4.5 petrol and compared to what i have now it's almost identical fuel figures, with a lot more power. I find that I only have to press lightly on the go pedal to get the thing to go. and if you boot it, it shoves you back into your seat and hang on... Doesn't have the same control as a sedan, lol.. Have heard about Terrain Tamer doing a gearbox gear change for 5th gear, to lower rpms, so lets say 2600 rpms at 100kph, versus 2200rpms at 80kph. I get better fuel consuption sitting on 80 kph than I do at 100kph.. If I could sit on 100kph at 2200rpms I presume that my fuel cosumption will be similar to sitting on 80kph... Thats why I'm asking about gearbox ratio changes rather than diff ratio changes.... Am hoping to find someone on here that has done it or knows of someone that's had it done... Cheers
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Follow Up By: get outmore - Tuesday, Apr 03, 2012 at 20:16

Tuesday, Apr 03, 2012 at 20:16
Your assumption is wrong. It takes alot more power to do 100 vs 80 regardless of revs
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Follow Up By: Madfisher - Tuesday, Apr 03, 2012 at 21:52

Tuesday, Apr 03, 2012 at 21:52
50% more wind resistance at 100 then 80 if memory serves me correct. As soon as you increase your gearing upwards you have to put your foot down more.
Cheers Pete
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Follow Up By: GET ON ! - Wednesday, Apr 04, 2012 at 19:53

Wednesday, Apr 04, 2012 at 19:53
Your replies make good sense to me. Never thought about how much extra power is required, or about the force of wind resistance. Thanks guys.
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Reply By: Ross M - Monday, Apr 02, 2012 at 22:26

Monday, Apr 02, 2012 at 22:26
G'day Get On
Most petrol vehicles get the best fuel economy with less than the overdrive 5th gearing. So to get fuel economy you would be better to get an overdrive ratio which is 4th and a half.
All fuel efficiency trials all run in 4th, never 5th.
Most people are conditioned from birth to believe 5th gives economy and it aint necessarily so.
Cheaper than two diffs and 5th gear ratio changes etc.

If you are towing then smaller Dia tyres will lessen the load on the engine, let it spin slightly quicker and the resulting less throttle opening may give more economy.
Borrow some wheels from someone else and try it, youmight be pleasanlty surprised.
Bigger tyres, wider tyres will always use more fuel.

By using really good oil in your engine you will also increase the efficiency and any extra revs won't be a worry.
What fuel do you use?
If you use the highest octane fuel you can afford it usually uses less for the same distance.
My use of 98 octane in some engines often means it is actually costing less to go the same distance. Yes, it saves money.
Don't use Shell fuel as it hasn't proved to be the best one around.
BP and Caltex 98 octane do ok.

Ross M
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Follow Up By: GET ON ! - Monday, Apr 02, 2012 at 22:30

Monday, Apr 02, 2012 at 22:30
Thanks Ross.
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Reply By: george50 - Monday, Apr 02, 2012 at 22:51

Monday, Apr 02, 2012 at 22:51
Totally agree with Ross on that , Get On . I fitted 285x75x16s on my FZJ105 partly to drop revs and gain economy. Yes dropped the revs about 300rpm in 5th but economy was worse . Fitted extractors after crushing the std. system in the bush, sounds nice but negligible improvement. I don't think you'll get a big improvement without spending heaps on the motor .
AnswerID: 482208

Reply By: Member - Tour Boy ( Bundy QLD) - Tuesday, Apr 03, 2012 at 06:16

Tuesday, Apr 03, 2012 at 06:16
Hi, The 1FZ is most economical at approx 2700 rpm. Try a drive in 4th to bring the revs up and see if it works for you.
Cheers,
Dave
2010 Isuzu FTS800 Expedition camper
2015 Fortuner
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Follow Up By: GET ON ! - Tuesday, Apr 03, 2012 at 20:00

Tuesday, Apr 03, 2012 at 20:00
Hi Tour Boy, Thanks for your reply. Just thought I'd investigate a theory that I had, mmm, another theory bites the dust,Lol
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Follow Up By: Madfisher - Wednesday, Apr 04, 2012 at 20:13

Wednesday, Apr 04, 2012 at 20:13
Tour boy out of interest what are max torque revs in the 1fz motor.
Cheers Pete
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Follow Up By: Member - Tour Boy ( Bundy QLD) - Thursday, Apr 05, 2012 at 06:10

Thursday, Apr 05, 2012 at 06:10
Hi Pete,
It is at around 2700rpm but develops more torque at idle than the 1HZ does at it peak.
Cheers,
Dave
2010 Isuzu FTS800 Expedition camper
2015 Fortuner
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