HJ61 12H-T mods

Submitted: Wednesday, Apr 19, 2006 at 22:00
ThreadID: 33062 Views:6036 Replies:6 FollowUps:3
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1 want to improve economy and reduce RPM on the highway
am looking at changing dif ratio from 4.1:1 to 3.7:1
has anyone done this/offer advice?
also considering increasing wheel rolling diameter
currently running 31" x 10.5" R15
are there 33" x 10.5" R15 road tyres available and will they fit ok?
will i need to go to R16 rims?
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Reply By: Member - Davoe (Widgiemooltha) - Wednesday, Apr 19, 2006 at 22:18

Wednesday, Apr 19, 2006 at 22:18
I dunno how much diffs are worth but I am guessing around 1500 each = 3 grand.
That is alot of fuel you would have to save. And if you go offroad much the higher gearing will be a pain especially in low range where th 60s have a 2/1 transfer case ratio. Running bigger 15 inch tyres could well negate any fuel savings due to their larger width. best option for purely fuel saving would be 235x16 inch tyres
Personally I reckon whatever you try will be alot of cash to spend on a 10 grand 4by to alter what is a pretty good setup to start with
AnswerID: 167943

Follow Up By: Tim HJ61 (WA) - Thursday, Apr 20, 2006 at 17:07

Thursday, Apr 20, 2006 at 17:07
New tyres are one thing, but a set of new rims as well and the cost really starts to add up.

I get a pretty consistent 8km/l out of my 12HT, but of course are looking for more. Have to agree with dropping the speed being the most helpful thing. I normally sit on 100km/h on the GPS = 106 on the speedo = 2450 rpm. Initially had wanted to drop that down a couple of hundred revs but I can do the same by installinga a liftem foota bit.

Enjoy your truck.

FollowupID: 423350

Reply By: Dave198 - Wednesday, Apr 19, 2006 at 22:32

Wednesday, Apr 19, 2006 at 22:32
My experience with my HJ61 to improve the economy is stay around 95kph.
5 or 10 minutes longer to get there, but saves a lot on fuel. I would agree with Davoe, and how easy to get the tyres if you bust one in the bush?
AnswerID: 167947

Reply By: Muzzgit (WA) - Wednesday, Apr 19, 2006 at 22:39

Wednesday, Apr 19, 2006 at 22:39
Mate. After running "small" tyres on my petrol 60 series I went to 33 x 10.5 R15 BFG AT's.

Better fuel economy? I didn't check but I doubt it.

Lower RPM on the highway? Yeah, a bit, but speedo was out of whack which cuased my photo to be taken, twice!!! (both on long weekends-double demerits)

Better off road? You bet ya! What I lost in torque (bugger all) was more than made up for by the easier driving in sand, rough roads, rocky stuff.

More proof that the height of the tyre plays a bigger role when off road than the width.
AnswerID: 167950

Follow Up By: Member - Davoe (Widgiemooltha) - Thursday, Apr 20, 2006 at 00:01

Thursday, Apr 20, 2006 at 00:01
yea sorry of course bigger tyres will give better performance off road although as i understand hill engine braking can be effected and you might have to use low range earlier for slow stuff
FollowupID: 423207

Reply By: jelm - Thursday, Apr 20, 2006 at 22:19

Thursday, Apr 20, 2006 at 22:19
thanks for responding guys
this is how i figure it
the hj61 is in pretty good shape - inside and out - for a 20 year old vehicle - mechanical seems ok and it's very straight, neat and tidy with 240000kms on the clock - cost $8,500 - we got it for it's size - can seat 8 and tows the camper ok - we want it mainly for the highway - between adelaide and sa's west coast - will do very little off road - maybe a run along a beach or dunes and a bit of dirt a couple of times a year - i can spend a grand on an exhaust, a grand on an intercooler, 1500 to get BOTH diffs done and another 1500 on some 33" tyres - so thats 5 grand plus the 8.5 purchase cost makes it $13,500 and it should hum on the highway, pulling the camper and last another 20 years - so i am just doing the homework at this stage - thanks again for your replies/knowledge/advice - much appreciated
AnswerID: 168197

Reply By: Member - DOZER- Saturday, Apr 22, 2006 at 08:32

Saturday, Apr 22, 2006 at 08:32
Marks adapters sell transfer gears that are higher on the highway and lower in low range....might be the go, cheaper than diffs, but in all fairness, you are chasing yout tail with economy.....8km/l is about right. the cruiser weighs 2 tonnes off the factory floor, and you probably have bars and suspensionlift on it aswell...Bigger tyres will help your revs/100kms and probably make it cruise easier, but the braking performance will suffer thesame % as the revs drop....and the 12ht doesnt mind the revs....you could intercool it....but you would get more power out of it then, and want to use it....lol
Life is a compromise......gr8 truck
AnswerID: 168440

Follow Up By: jelm - Sunday, Apr 23, 2006 at 21:14

Sunday, Apr 23, 2006 at 21:14
thanks dozer - i'd be happy with 8km/l !! last trip towing the camper (jayco) we got only 5km/l !! - just did another weekend trip towing the camper and got about 6km/l this time - sat on around 100kmh instead of 105kmh - but it's still a bit low- i'm just going to go over the basics first - valve clearances, injector condition & timing then i'll give it another run and see if it improves.
FollowupID: 424011

Reply By: Member - Pezza (QLD) - Sunday, Apr 23, 2006 at 23:11

Sunday, Apr 23, 2006 at 23:11
G'day jelm,
Rather than me writing it all again, I hate typing, it might be easier if you read thread 32059.

AnswerID: 168664

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