VT V6 5 spd manual final dive ratio diff uncertainty

[shdai]

gday guys i have really small gear ratios in my manual VT V6, for example first gear red lines at about 30-35 km/h and sitting on the freeway doin 100km/h the cars screaming at 3100 rpm. im fair sure this isnt normal and i think the dude that i bought the car off has mucked around with the Final drive ratio but i dunno. i want the original gearing put back in the car but dunno where to start or what the problem is cos ive taken a look at the diff and the little sticker says EC 3.08:1, this is what im meant to be running. can someone tell me whats goin on here please. im just sick of the car chewing through litres of fuel all the time.

[50LTRv8]

Are you sure it is going up all through the gears? maybe change them manually

Sorry, just read your on manual

[keza87]

It sounds like you have a high ratio diff in there. Mine sits at about 2300 at about 110km/h in 5th

[shdai]

yea thats what i thought in the beginning but the diff decals saying 3.08, and i have also checked gregorys manual which says the ratio that should be running is 3.08, it doesnt specify if this is for auto or manual though. i was thinkin of jus buying a second hand 3.08 diff n sticking that in to see if it will fix the problem? mayb put a 3.07 in instead?

[old mate]

3.08 ratio is for both auto and manual. you can check what the ratio is fairly easily if you jack the car up and turn the tailshaft around until the wheels do one full revolution.

with a 3.08 ratio diff, the tailshaft will turn 3.08 times for each 1 wheel revolution.

or you could just post up what wheel and tyre size you have on the rear and i could work it out for you.

or you could pull the cover off the diff and read the markings on the crownwheel. should have the ratio marked on it, i know the 3.08 ratio gears do.

[shdai]

oh ok so is it a possiblilty that what the ratio on the diff housing is reading is actually different to what its running? its an LSD btw and my speedo is out by exactly 18kmh if that helps. im running 235/45R17 all round. thanks for the help mate...

[old mate]

yeah i would think that the ratio has been changed, but the stickers on the diff still say 3.08 ratio.

3.08 ratio gears would mean it would do 2055rpm at 100 km/h

so if you are doing 3100 rpm at 100 km/h you have a diff ratio around 4.6 to 1. are you sure its doing 3100rpm at a true 100km/h? that would be death on fuel. i dont think my maths is out but thats a seriously short diff ratio if i got it all correct.

hmm... does it feel like it acclerates really hard for a v6? i spose it would if it redlines in 1st at around 35 km/h

[shdai]

mate its rediculous...i can shift from 1st to 5th and u wouldn even realised ive skipped 3 gears if u werent sitting in the passenger seat. im certain its revving this high at 100kmh. thats exaclty why i wanna get my original gearing bak (too much fuel!!) but dunno wat the culprit is! i dont even bother starting in 1st gear n e more, its pretty much pointless cos i hav to change as soon as i pop the clutch.