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Post by nikolaiv on Sept 19, 2005 19:31:26 GMT 11
We`re on our second set of 265/75 R16 BFG Mud Terrains on our 1994 LWB Irmscher, and I`d love to change the gearing so that we didnt lose as much performance (it`s a big change from the 245/70R16 stock tyres...)
does anyone know what other diffs we could fit to lower the gearing slightly? or failing that would a big bore exaust and injector rebuild be a better option?
Its an auto, w/185kms on the clock, (new turbo 40k ago etc) and we service it religiously every 5k, but it just feels down on power, and its started to use more diesel.. used to be 600km`s till fuel light, now 530km.. (and i do adjust for the increased rolling diameter of the tyres...
We want to keep the big tyres as my everyday use includes a fair bit of dirt driving, and some more torque/power would be appreciated.
Looking forward to your replies...
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Post by geeves on Sept 19, 2005 20:38:05 GMT 11
Same year diff heads from a petrol modle will be 4.5 instead of 4.3 All other choises on ratio involve a lot of work. Try the big bore exhaust first as it should be ok on that size tyre. A few people here have noticed problems when going to 33 inch tyres yours are just over 31 inches
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Post by mudgrip4 on Sept 19, 2005 21:44:36 GMT 11
There is a drop off in performance esp in acceleration over 80ks after fitting bigger tyres. Is however easy to tune the isuzu motor to compensate. Advancing injection pump timing, adjusting for more diesel to flow through, putting in performance air filter - e.g. K&N, bigbore exhaust system esp ex turbo - 2.5 or 3", and have a look at mulover's new air intake pipe. Some or all of these will certainly give you big gains in kw and torque - might be easier than altering ratios, diffs etc, through whole drive train. Check earlier threads for discussion on performance mods.
Your 265/75/16s are 32". Mine runs these also and I found slight fuel use increase on the road after changing from 30", but performance tuning means it runs v well with the 32s. Mike
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Post by nikolaiv on Sept 20, 2005 14:32:31 GMT 11
Any ideas what i should do first? and any one able to recomend a good diesel garage down here in dunedin to carry out the work? I drove a 3.0TDi Prado teh other day, and if i could get the isuzu to pull like that i`d be a happy man...
I`ve noticeed recently that it`s smoking a bit on accelleration (black smoke mind) and i imagine that having the injectors rebuilt and adjusted should help economy and performance.
Cheers mudgrip, i didn`t think the tape measure lied about the size of the tyres ( i knew they were 32`s...)
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Post by mulover on Sept 20, 2005 17:21:45 GMT 11
Start where you can afford to, the exhaust will make a big difference in accelartion but not so much to top speed, I have 32" as well and i've got nothing after 110km, It all really depends on your wallet, i'm an engineer so i do all these things myself which reduces cost, but all the suggestions are very much worth doing.
Hey mudgrip4, how do you advance the timing? I have heard this makes a big difference, could you please let us know in simple terms!! Thanks,
John.
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Post by mudgrip4 on Sept 20, 2005 21:24:11 GMT 11
The 265/75/16 muds (hankook) are 810mm or 31.9", a very good tyre size retaining open road performance and adding the height and softness for off road. Good choice.
Not hard to gain 40hp and 100nm extra torque. The 2.8 standard is 110hp and 225nm of torque. After a bit of tuning mine dynos at 155hp and 340nm torque, and it goes like it. Will comfortably outperform a 3.0 prado, with top speed of 150ks plus on 32s. On 30" tyres, 80 - 110ks was 6.4 seconds, quite snappy really.
Cheapest and quickest tuning is advancing diesel pump injection timing - 30 minutes work - this gave me about 15hp extra. Also gives 500rpm more of useful power at top end from 3000 to 3500. Can't recall exactly how, but diesel mechanic could do this. Will talk with mechanic friend.
Second step is to increase diesel flow on fuel delivery screw at back of pump. Increase in small increments ( eighth or even twelfth of a turn at a time until starts to blow black smoke at 3000rpm - then come back a click - just before heavy black is was point of greatest hp on the dyno. This should be done with the pump advance - takes 20 minutes? Can be 10hp.
Third easy thing - go get a good free breathing air filter like a K&N of a unifilter. K&N slightly better and a bit dearer but both good. K&N was $105 trade for mine. Small but perceptible gain when up in the revs and the engine is trying to suck in more air. 5 - 8 hp gain?
This is not a bad start for tuning and shouldn't cost much. Some downsides to consider. Increase the tuning/power and your motor may not last as long. Never advance injection timing to the point that motor starts to idle a little rough. And be aware that if you put more diesel through, unburnt diesel can pollute your engine oil quicker and you might need to do changes at say 4000ks instead of 5000 if running very rich.
2.5" bigbore on mine ex turbo added about 8 - 10hp and changed torque band of motor. Added 500revs of power at bottom end so truck now pulls hard from 1500rpm, not 2000 as before. Cost $440 to $750 for mandrel bend. Sounds like a cross between an Austin Healey and a chainsaw now..
And there's always mulover's free flow air intake - showed the picture to a clubmate at Autobend and he says he could mandrel bend one for about $70. I like this idea - can you estimate mulover what power % gain it gave you?
So there are some tips - ring around some diesel or 4x4 shops and someone could do the first 2 for you. Should help. Mike.
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mumad
Isuzu Baby
Posts: 4
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Post by mumad on Sept 20, 2005 21:58:29 GMT 11
Hey mudgrip, i would say it would be probably about a 5% gain, at a rough guess, it just lets the motor rev alot better now, am thinking about making a bigger top for my snorkel to get more air in too.
Am real keen to know about the timing advance, cause i only want some more top end power, i have plenty down low cause i keep breaking things!!!
Am also going to mount a fan on my intercooler and see if that makes a difference, its going to be great to have a work vechile so that i don't have to worry about having my truck ready to go every day!!
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Post by mudgrip4 on Sept 21, 2005 20:17:24 GMT 11
Nikolaiv - remember to factor in speedo variation from 245/70s to 265/75s - about 7% it seems - when assessing performance. My club has a link to a tyre chart which can give useful comparisons - though mudgrips are a little bigger than the heights given. Club site is cr4wd.orcon.net.nz, (Canterbury Recreational 4wd club) and click on signpost at bottom for links. When you get to link, if nothing shows but a grey patch, click on the bit of purple text.
Also a useful link there is the weather site titled " Christchurch weather, and other locations worldwide". Enter your location in small panel up top - for 7 day preview. Probable useful for Aussie as well. Mostly well known locations. Mike.
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