Diff ratio quandry...

[Pumpy]

After trundling across France last week, I found running 315's a bit tedious trying to keep up with a D4, RRS, and a remapped TD5 90 rather tedious at Payage speeds, or the slightest hill, had to use low box to get up the tarmac switchbacks without overheating the ATF. It's a bit disconcerting when the box changes down at 75mph for a bit of an incline too I wasn't really happy keeping my foot to the floor for 800 miles trying to keep up while watching everyone disapear into the distance either!

With a 115mm lift it's going to look rather odd going back to stock 31" tyres, I'd also have to trim the side steps to avoid sitting on them in the rutts on UK lanes, so I'm debating having the diffs done.

Reading a bit yesterday I came across two sets of recomendations for 35" tyres, either 5.56 or 5.88 both recomend driving a truck with the new ratios beforehand to help decided which I prefer, since I doubt that'll be possible, I could do with some advice before I get spendy.

Advantages/Disadvantages of either ratio?

I'm still in two minds, having a set of smaller tyres for overland could work I guess, but either way I'd be throwing a chunk of cash at it...

 

[Shayne]

How about power upgrades ?

 

[Pumpy]

How about power upgrades ?

What are the options Shayne? It's got an intercooler, don't know how long ago the pump was turned up before I got it, but that's what caused the pistons to crack so I'm not keen on turning it up again.

 

[Shayne]

Can't say i have ever looked at the options for an 80 i just thought an intercooler and exhaust upgrade might add a few horses to balance things out .

I don't think i would have problems keeping up with your convoy in my 90 but i can say for sure i will never have to slow down to wait for Chas in his auto 80 which might be a 12 valve ?

Heat likely cracked your pistons so a 3" exhaust and the pump tuned by someone who knows what they are doing might make all the difference .

Supposition though it was just a suggestion that someone with experience of tuning that lump of 6 might elaborate on .

 

[madmanmart]

My old mans truck has a custom intercooler, 4" exhaust system, electric fan conversion, egr delete and the pump tweeked. It really moves but is running standard size tyres.

 

[StarCruiser]

4" exhaust…? I bet that burbles nicely

 

[Chris]

In a 24v Manual, just stick 12v autos diffs in. I'm running 35's and I think that those who have been in it will vouch it doesn't lack any grunt or top end. Really no need to go bonkers. I only had 4.56 with 37's on. What are auto diffs, 4.1 IIRC from 3.9 in the 24v manual?

 

[Pumpy]

sorry Chris I shoulda said, this is a 92 12v Auto.

 

[Chris]

Dang. If that was in your signature line .....

Same applies though in terms of steps. You don't need to go all super ratio for 35s.

 

[Pumpy]

there was abit of a clue, not many manuals get overheating ATF

if it's not diff upgrades, what's the answer given the OP?

It'd be nice to have the courage to overtake something, even better if I could overtake on an incline.

 

[Jon Wildsmith]

3.7's in a manual, 4.1's in an auto. 4.88's would over compensate for the 35's but that's usually a good thing on an 80 carrying a lot of extra weight. If you haven't already, get yourself a 3" exhaust including dump pipe and a EGT gauge so you can see if you're getting all you could in terms of fueling optimisation.

 

[Pumpy]

Thanks Jon, is there anywhere you'd recomend for the exhaust and EGT gubbins? any idea on ballpark price?

 

[Pumpy]

just sent an enquiry through Powerflow, WTH it's only money

 

[Shayne]

Prospeed Cardiff for exhaust

 

[Jon Wildsmith]

Pro Speed are good. Ideally you want the new exhaust to include replacing the elbow that bolts directly to the turbo (dump pipe) and run inside the chassis rails. The OEM elbow is restrictive as are the extra bends if following the OEM pattern. No idea on price, I made my own when I last had an 80. Try one of the Landcruiser specialists, they may have access to an off the shelf kit if not for the exhaust then for the EGT gauge.

 

[Roger]

I run 37's - on a 12v with 3.7 diffs - never had a power issue - can keep up with the best of them it seems.

My problem is that at 60mph my engine revs were so low that the oil pressure remained low, I take a caravan to a lot of offroading events and wasnt happy with loading the engine with the van with low pressure - I often found myself dropping into third to get the engine to spin up and bring the oil pressure right up.

I did my homework and concluded that 4.56 ratio would bring me slightly lower than factory spec (a good thing as mentioned in above posts imho) and whilst Im at it, Ive gone for 33% lower crawler gears.

Karl may have some better ratios for you I believe.

Fitting in the next week or two - will report back.

Personally, with 5.56 or 5.88 I think you will be way too low and whilst you will get up to speed quicker, you will run out of Revs and be screaming.

 

[Chris]

Yep, I ran 12v auto with 37's and 4.56s. Spot on. Never noticed any difficulty cruising at 70. Nor in pulling away. Didn't change low range. Never felt that need.

 

[Roger]

Yep, I ran 12v auto with 37's and 4.56s. Spot on. Never noticed any difficulty cruising at 70. Nor in pulling away. Didn't change low range. Never felt that need.

Im only changing low range for the hell of it to be honest - its bragging rights after a few beers at the trials

 

[Chris]

Excellent, nothing wrong with a quick brag in between sips. Try to look nonchalant when you say it. Worth extra creds.

 

[Pumpy]

Roger did you order direct from Nirto-Gear? What was the total for two diffs inc fitting kit/shipping/duty etc? just trying to get a ballpark figure for the costs.

Have I got this right?

DIFF RATIO FORMULA

Larger tyre size divided x standard tyre size
35” divided by 31” = 1.1290 which = 12%

To calculate correct ratio - Standard diff size x 12%
example - 4.10 x 12% + = 4.592

Will the standard lockers still work too?