Td42T, 5th gear overdrive help

[Bigute]

G'day, been trying to find information for this for a while but can't seem to find anything for the TF plenty for ZD,

I have a GU ute on 35s with 4.6 diff gears, around town on the 95L tank it gets about 850-900kms but on the highway I get around 300-350kms I had the fuel pump replaced as mine was shot and that didn't help.

the only thing I can think off is around town it gets babied and I change around 15-1700 rpm and tops out at 70-80km/h, yet on the highway its non stop at about 2300 for 100km/h I'm looking at the 5th gear overdrive however its only a 10% reduction in TD42's and that hardly seems to justify the $1700 for the gear + $155 for the extended spline.

Has anybody done this on a td42T did the 10% make a massive difference I was really hoping to have it sit around 1800 but that seems like a bit of wishful thinking at the moment?

[mudski]

you have 4.6 gears, and in fifth at 100kph your doing 2300 rpm? Surely not. Mine in 5th sits on 2400 with 4.11's. I had 4.3's prior and it was doing around 2600 rpm. Somethings a miss there.

[Bigute]

I'll double check on the weekend its in getting a service at the moment, but yeah still need it to come down, it revs way to damn high lol

[mudski]

I'd be getting the speedo checked aswell.

[nipagu7]

there could be other issues at play . what engine mods do you have , snorkel , 3' exhaust , airbox , bigger turbo / intercooler . is the IP standard . has it been tuned on a dyno ,a dyno can help show up other components that are not working right/efficiently at higher RPM .

[Bigute]

Snorkel and 3" exhaust thats it, the no other engine mods didn't want to muck with that too much.

speedo was checked at engineering and also do a bit of traffic work so have checked it against calibrated speed devices

[mudski]

Something is not right. TD’s will happily sit at 2300 all day long. They hate anything under 2000rpm, but you have 4.6 gears so this will change a lot.
Mine is tuned at 170rwkw and 700nm on 33’s with 4.11 diffs and at 100kph it does 2400 rpm. I will see around 16L/100 on the highway. When I had 35’s it was just under 2200rpm.
Fuel usage will only change if I’m hauling a heavy load.
Get a gps app on your phone and see what speed it says compared to your Speedo.


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