Another Diff Gears Question

[darnoldrs]

I have a TD42t St wagon with a 4 inch lift, 315/75/16 tires and will have a top mount IC, High flowed turbo, 3inch exaust and tune.
I am looking at either 4.3 diff gears or 4.6. 4.3 will be slightly taller than standard and 4.6 a little shorter so my question is...
Am I likely to get better highway fuel economy running 4.3 or 4.6 diff gears. I will be fitting rock crawler gears so low range is not a consideration.

actual speed when spedo is showing 100kmh
Metric Tyre size 3.9 4.11 4.375 4.625
30 98.007 93.000 87.366 82.644
265/70/16 30.61 100.000 94.891 89.143 84.324
31 101.274 96.100 90.279 85.399
265/75/16 31.65 103.398 98.114 92.172 87.189
32 104.541 99.199 93.191 88.153
285/70/17 32.7 106.828 101.369 95.229 90.082
285/75/16 32.83 107.255 101.774 95.610 90.442
305/70/17 33.83 110.519 104.872 98.520 93.195
315/70/17 34.3 112.055 106.329 99.889 94.490
315/75/16 34.6 113.035 107.259 100.763 95.316
35 114.342 108.499 101.927 96.418

RPM @100kmh 2250
Metric Tyre size 3.9 4.11 4.375 4.625
30 2296 2419 2575 2723
265/70/16 30.61 2250 2371 2524 2668
31 2222 2341 2492 2635
265/75/16 31.65 2176 2293 2441 2581
32 2152 2268 2414 2552
285/70/17 32.7 2106 2220 2363 2498
285/75/16 32.83 2098 2211 2353 2488
305/70/17 33.83 2036 2145 2284 2414
315/70/17 34.3 2008 2116 2253 2381
315/75/16 34.6 1991 2098 2233 2361
35 1968 2074 2207 2334
Thanks, David

[darnoldrs]

table didnt work properly and it is a GU series 2.

[turbo gu]

Had both in a GU 4.2td. Its only mildly modified, eg 3 inch, touch more boost and fuel with same lift and tyres as you.
Go the 4.3s, far more relaxed to drive. Started with 4.6s cause that's what everyone said you should run. Swapped to 4.3s around 5years ago and would only swap back if going up to 37s

[darnoldrs]

Thanks for the reply.
I was leaning towards the 4.3 but everyone seemed to be going for the 4.6 ratio and didnt what to do it twice.
4.3's will be ordered and go via ARB lockers on way to my car.
Thanks for the confirmation of my conclusions.

[turps]

Was talking about this issue yesterday.
For a GQ with 35's we think 4.3's would be perfect for touring. I used 4.1's with 33's and it was pretty good. Speedo read a fraction slow. But my GPS lived on the dash, so I just used that. 4.6 gears with 35" tyres also works out that the engine is doing approx 2600rpm. similar to running 4.1 gears and 31" tyres.
Where as 4.3 gears with 35" tyres is approx 2400rpm, which is a nice spot on the rev range. And with a Hiflowed turbo it should be in a sweet spot for quick response.

[surrender]

I run GU diffs with 4.6's and 35's on my GQ, the gears are quite short and revs sit a little high at 110km.. Not unhappy with it though, gets the power to the ground and doesn't phase me enough to change it to 4.3's although I am about to go up to 37's which is where the 4.6's should be just right. I think it does come down to how you want the vehicle to drive. In saying that, for touring purposes I would agree that 4.3 and 35" would be the best match.