DIY Budget Bighorn Project

[andy]

Hey guys, I've been away from Isuzu's for over a year after a brief ownership of a Mitsi Challenger but i'm back again with a 1992 Isuzu Bighorn LWB Irmsher 3.1TD.

I picked up my truck on trade me for $2610 with a fairly high 286,000km in grey but its straight with good paint, 5 speed manual and it seems to run very clean and not using much oil.

With a budget of approx $4k for the whole project i had to be fairly smart with my money!

First off i bought some wheels off trade me as the factory black steelies looked terrible and i wanted the freedom of 15in tyres. Some 15x8.5's turned up on trade me for $300 in a 0 offset. They were fairly oxidised upon pick up so i took them into work and bead blasted them to get them clean and smooth and threw a can of silver metallic aerosol paint on them which worked a treat.

Next up i managed to score a deal with a mate who knew someone that imported tyres so i scored a set of Nankang N889's or Mudstars in a 33x12.5x15 for $200 each plus $80 for fitting and balancing.

I found some duraflares on trade me which were for a holden jackaroo for $220 but needed a fair bit of work to get them mounted. I mocked up the flares onto the guards using tape to hold them in position. Then made up some alloy sheet tabs which i screwed to the lip of the guards as shown.


I then bought a fibreglass kit from Repco and glassed the tabs to the inside of the flares.


Once dry i removed the flares, added some extra firbreglass to strengthen it up nicely and then refitted with the supplied rubber strip.

The first thing i noticed was that the tyres hit the front bumper on full lock so i had to trim it to suit. I fired up my jigsaw and made a cut 2 inches forward on an angle 6 inches up as shown



Next up i wound up the torsion bars (clockwise) to raise the front of the truck 25mm which gave me clearance to get full lock and clear the rear of the wheel well. I'm still scraping slightly when reversing and turning at speed so i'm thinking of either raising it a bit more or cutting away some of the inner guard to gain another inch or so clearance.




It was about then that my starter motor decided to crap itself so back onto trade me i went to search for some bighorns being wrecked. A guy in Manakau was wrecking one and offered me a starter motor for $60 and also had a rear diff for sale. I did a little research and found out the option code for an LSD rear diff was G80 and this had that on the option plate. Managed to get that for $90 ;D and went about installing both the starter and diff (41 tooth crown wheel by the way so the auto's and manuals are identical ratios).

Decided the factory leather steering wheel was past its used by date so replaced it with a 360mm leather wheel bought off trade me for $90 and bolted straight onto the factory Irmscher bosskit with a little modification to the horn wiring.


I then stumbled across some $20 boost gauges from STA parts out by the airport so thought i may as well get one as i'm planning on playing around with turbos and boost pressures etc later down the track. Was easy to plumb in by teeing into the intercooler pressure line as shown.


As you can see the above mods have completely transformed the truck though i have lost a little bit of acceleration due the size of the tyres i'm running.

Running total so far
$4270

[muvit madness]

Hi andy
nice work seems you've been busy how quickly the dollars add up eh?
liking dem tyres too they look chunky & you scored em for a good price.
good luck with your bighorn looks great

regards
muvit

[andy]

Thanks mate

Took it down south for its first trip away and i was most impressed. Firstly the tyres are freakishly quiet, my last ones were BFG mud terrains in a 33 also and they were far noisier and even the road orientated grand trek's it came with had more rumbling.

Drove from Kumeu just out of Auckland down to Bulls in 5.5 hours which is about 500km and it just sat on 100km/h the whole way. I got 650km out of the tank and averaged 9.5km/L.

The only concern i had was that it used about 500ml of oil for the 1200 odd km's but i guess this isn't the world

[mjrstar]

hey loz... this could be a handy thread for others attempting to fit 33's without a body lift...looks like you are ready to try out the lsd and tyres now, it's pity my truck is still nana on-road spec at the moment.

[andy]

I had a look at my air filter yesterday and found it was looking fairly black.

My mate (MJRSTAR) suggested a pod filter setup as found at repco as it would cost about the same as a paper element type filter and is cleanable and should flow a lot more.

Here's what we came up with. I welded a 1 inch piece of 3 inch steel pipe onto the hat of the air filter which would have actually been a press fit if i had persisted a bit longer. Welding is more fail safe anyway.



I then fitted a mushroom foam filter made by wildcat ($39.95 from repco) which fitted perfectly within the factory airbox and whilst not as good as a K&N i can't really justify the extra expense for bugger all extra gain.



There is a noticeable increase in response throughout the rev range but the best bit is the top end which has been extended from 3200rpm to about 3600rpm before getting lethargic. All in all, a very good result for cheap ;D

[mudgrip4]

Have a chat with a friendly diesel mechanic and ask him to advance fuel pump timing - this gives a good increase in power again. Takes less than half hour - added 15hp to my 2.8 - and specifically added power to the top end.

Mike

[geeves]

Not sure you would want to do that to a 3.1. Advancing the timing will generate more heat esspecialy if you use it. The 3.1 is not as tolerant as the 2.8 to heat. The 3.1 already has fairly good power characteristics so less need to tweak.
Its good to see someone else using a foam cleaner I have a unifilter in mine which is a straight replacement for the factory paper element but almost everyone else has gone for K&N or other cotton pods. If that is a single layer foam do clean it at least every oil change and oil as per instructions If they dont recomend an oil to use use the unifilter brand oil. It is designed for foam and is different to the oil for cotton filters.

[dxmedia]

Have you blanked both the erg valves? OR if you blank on the left of the engine you can take that bleeding annoying pipe from over the top of the rockers off...

You'll get shed loads more low end torque (5th gear at 25mph), better fuel ecomony, BUT an increase in N0 for your vehicle emissions (do you guys test for N0?) - I know they do in the states, but in the UK we don't.

[geeves]

Were luck in clean green NZ For cars already here the only emmisions test is a visable smoke test which my 4jb1 can pass stone cold ie if you can see out the back its a pass. New imports and new cars though have to meet Euro 4 standards but dont know if they will actualy be testing at WOF time

[andy]

dxmedia said:

Have you blanked both the erg valves? OR if you blank on the left of the engine you can take that bleeding annoying pipe from over the top of the rockers off...

You'll get shed loads more low end torque (5th gear at 25mph), better fuel ecomony, BUT an increase in N0 for your vehicle emissions (do you guys test for N0?) - I know they do in the states, but in the UK we don't.

Yes i did that 2 days after i bought the truck! used some 0.063" alloy sheet to make a gasket that blocked it up but retained the factory appearance to keep the WOF man happy

mudgrip4 said:

Have a chat with a friendly diesel mechanic and ask him to advance fuel pump timing - this gives a good increase in power again. Takes less than half hour - added 15hp to my 2.8 - and specifically added power to the top end.

Mike

I don't think you mean advance the pump timing do you? This is generally a big job but what i think you mean is the fine adjustment screw on the pump to add or remove fuel throughout the range. I've played around with this before on my old challenger and had some interesting results. A very small adjustment ie 1/8 turn can be the difference from being gutless to over fueled and chugging gas.

I'd rather sacrifice a little power for better fuel economy as I do about 60km a day on the open road so raising the boost a couple of pound is about all i'll try to gain more power.

[mudgrip4]

No - was referring to advancing timing on diesel pump not increasing fuel delivery which also helps. The pump timing adjustment is very common - many 4x4 clubmates give their trucks a tweak, and it is not a big job - 20-30 minutes tops. 4JB1T 2.8 motor handles the extra tune with ease though might be a question with the 4JG2 3.1 which can crack heads.

Economy with my 2.8 was unaffected by higher level of tune - ran for 95,000ks tuned to 155hp and still returned 30-32mpg average over 5 year period.

Mike

[muvit madness]

Hi
All this talk about tweaking fuel pumps begs the question of how exactly is it done as i think i could benefit from this easy mod. can anyone shed some light in a step by step process please

cheers
muvit

[dxmedia]

Move the pump forward one tooth on the timing belt

[geeves]

The pump timing can be adjusted in the same way as a petrol dizzy but it doesnt take much before the engine starts knoicking etc I would of thought 1 tooth was too much.

[dxmedia]

without looking, I'd have thought that 1 tooth would be about <>5-7 degrees, it would be a good start. If it was knocking at that, then you know that it's less. If the power jumps up, then it's a good start. For the simplicity of jumping the belt a tooth, it's got to be the easiest option. Just mark everything with white paint before you start so it's possible to move it all back a tooth if needs be.

[Harry]

The first time I changed my cam belt I didn't know about locking the cam pulley and it advanced itself.The motor sounded really bad, a sharp vicious knock.I think 1 tooth is too much.The 3 bolts tha hold the pump onto thebelt housing are in slots to allow fine adjustment.You also need to loosen the bolt in the bracket at the rear bottom of the pump.The Rodeo motor with the gear driven setup looks to be harder to adjust.I haven't figured it out myself yet.
Hope this helps.
Regards,Harry.

[andy]

I would have thought adjusting the fuel delivery screw would be sufficient in most cases.

On a side note, the power steering belt snapped on the way to work on wednesday

Got very hard to steer with the big tyres all of a sudden! Certainly required both arms even on relatively open corners. $31 later its all fixed and i just hope it was an old belt and not a half seized pump or anything.

Also cured 99% of all tyre rubbing by "massaging" a little bracket behind the inner guard liner. Now i just need to find somewhere to take it offroad in the Auckland region to do some testing

[geeves]

If you managed to retrive the old belt check the inside surfaces for cracking. Very hard to snap a good belt as it will slip way before breaking point There should also be 2 belts for the steering and a wider one for the alternator. Also check the condition of this belt. A friend had a garage change his belts on a little Mazda. Garage changed the power steer belt but not the alternator belt which littraly fell to pieces 1 month later stranding in deepest darkest Porirua at night. (yes he didnt notice the alternator light)

[andy]

The belt stayed in one piece but was frayed and had separated so i'm guessing this is why it threw itself off the pulley.

The weird thing is that my truck doesn't have air con from factory so has an idler gear where the air con pump would be with only one "V". Therefore it only has one belt for the power steering which doesn't sound right to me even though there are empty V's on the crank pulley

[James W]

The single belt and idler pulley is as from factory and quite sufficient as there is not the load required to drive an air con compressor. Mine was the same from factory, but I took the opertunity to add an air compressor in place of the idler pulley... very handy