Question about a diff ratio :S

[2005vzute]

g'day all,

after reading up abit on tall and short diffs and their ratios etc it's pretty much told me that you'll get better economy and top speed from a tall diff, 2.87:1 for example..and very good acceleration from a short diff, for example, a 4.11:1

with the short diffs and better acceleration..does that mean that it's just going to rev its head off and be quick...so like, 1st gear will be very quick to get up to high revs..2nd gear will be very quick to get to high revs etc so i have to change gears quick if im going to take off hard?

or will it make the revs go up normal/slower but accelerate to a faster speed..for example...we all know how a stock vz v6 goes in first gear(manual)..it's abit short, doesn't go that fast...if i put a 3.46:1 diff in it..will it go through the gear really quick and give it a shit top speed for that gear, or will it accelerate the same but take it up to a faster speed

sorry if that doesn't make sense, but if someone understands me could you help me what does everyone think about a 3.46:1 or whatever it is LSD in a N/A alloytec?

[acarmody]

I believe that if you put in the 'short diff' ratio it will get change gears faster.

3.45 in a standard 170kw Alloytec wouldn't be a huge upgrade, I believe they are 3.07 from factory with only the Alloytec190 copping the 2.85(?) ratio.

[2005vzute]

not sure on what engine comes with what diff and so on..but my 175kw poverty pack ute has the 2.87 single spinner...so does my brother 190kw calais...so are you saying it's just gunna rev itself up quicker..which is why they give you more acceleration? my tafe teacher was saying that even the 3.7 ratio will have my v6 screaming off its nut, and it'd use a shit load of petrol

[acarmody]

No it won't suddenly become a fuel guzzler. Around town you will hardly notice any difference, cruising down the highway it will use a tin bit more because you will be cruising at a higher RPM.

For example I have a VX with the 4-speed auto, it used to do ~1800rpm cruiing at 100kph, and now it does ~2000rpm, that changing from 3.08: to 3.45 .

If you went with say 3.9 or 4.11 then your 1st and 2nd gears would be fairly short before changing, but 3.45 and 3.7 aren't terrible to drive with or anything.

You have the T56 manual gearbox right? It will be fine.

[2005vzute]

nah, vz v6's have the aisin d173 gearboxes...v8's have the t56 i think....hmm ok...it's gunna be a while till a change a diff anyways..i was just listening to my tafe tacher koz he transformed his stock vy r8 into a race car:P....have a look in my facebook videos if you like...i gotta get a video of him doing donuts in it yet:P haha

[bigdaddycool]

Depends on the use, drag race only car 4.11 , everyday driving 3.45 or 3.46 depending on what the diff is off. I run a VT 3.45 on my VZ Exec.. goes fine, spins the wheels a little easier so ur tyres will probably wear a little faster i've found

[2005vzute]

precisely what im looking for bigdaddycool hahahha...yea i was thinking that, 4.11 for racin n shit, 3.46 or whatever soudns good or my kinda driving:P haha...not too worried about tyres atm, they only just me like 80 bux each hahaha, whatever shit house brand they are:P

[Calaber]

What sort of driving do you do? If you do mostly city driving, in medium to heavy traffic, a drop in ratio from 2.87 to 3.47 will mean noticeably quicker take-off, substantially reduced top speed in each gear and noticeably higher fuel consumption on the open road. However, if you want a good compromise between acceleration and fuel consumption, 3.47 is probably the best ratio to choose.

If you don't care about fuel consumption, go to a lower final drive, such as 3.74. Going as far down as 4.11 will wreck the car as a streeter because it will be revving its head off in top and the gear speeds will all be too low - you'll be changing gears more frequently. However, it will probably go like a scalded cat with a 4.11 up to about 140kmh, after that, it will start to die.

[2005vzute]

yea i do mostly suburb/city driving..sometimes on the freeway but not for that long...what top speed are we looking at for my ute if i put in a 3.46?...i might sometimes go to track days or a skidpan day depending on how rich im feeling haha:P...i mostly want it for a bit of an increase in acceleration, but i don't want the gears to be heaps short, i think 1st gear in the aisin boxes are too short anyway so i don't wanna make it much shorter then what it already is...plus i don't wanna have it revvin off its nut, and be too high on fuel...if i get this new job i might be doin a fair bit of freeway driving, i don't mind increased rpm by abit..but not heaps..how many rpm difference are we talking about when we change from a 2.87 to 3.46? i don't really know much, aslong as its not gunna be cruising at 2000rpm with a 2.87 then 3000 with a 3.46 or something at the same speed.

thanks fellas

[Calaber]

yea i do mostly suburb/city driving..sometimes on the freeway but not for that long...what top speed are we looking at for my ute if i put in a 3.46?...i might sometimes go to track days or a skidpan day depending on how rich im feeling haha:P...i mostly want it for a bit of an increase in acceleration, but i don't want the gears to be heaps short, i think 1st gear in the aisin boxes are too short anyway so i don't wanna make it much shorter then what it already is...plus i don't wanna have it revvin off its nut, and be too high on fuel...if i get this new job i might be doin a fair bit of freeway driving, i don't mind increased rpm by abit..but not heaps..how many rpm difference are we talking about when we change from a 2.87 to 3.46? i don't really know much, aslong as its not gunna be cruising at 2000rpm with a 2.87 then 3000 with a 3.46 or something at the same speed.

thanks fellas

If my maths are correct, the difference in ratios is about 20%. That would mean that for a road speed that used to mean 2000 rpm in top, your revs would now be 2400 for the same speed. That's a lot and it would definitely affect the economy on the open road.

Around town, you would probably notice a bit of a drop in economy but your in-gear acceleration would be much brisker. However, if you have a very short first gear, which is why the car has a 2.87 final drive in the first place, you might find that first is almost useless and you are changing into second very quickly.

[2005vzute]

first is almost useless to me now, i only use it to get the car moving and get a little bit of pace before going into second...maybe i might put in a 3.08 or whatever it is..eh, im a little while away from doing diff gears so i'll have a think about it

cheers mate

[cummo14]

sorry to barge in guys but i have a vz calais 190kw "auto" with the 2.87 gears, if i was too change them for 3.46 would my 0-100 speed increase by much?? to be honest i just want to be a bit quicker than other stock calais and sv6's lol

[VzVzVz]

I'll be changing mine from 2.87 to a 3.89. Hoping for a better jump off the line and better clutch kicks in 2nd. It should actually help my fuel economy to be honest, because the engine will be less laboured in 6th gear. thats the theory. Also to get a LSD that actually works would be nice.

[W45H1NGT0N]

cummo14: hey man yeh you'll notice a change in your launches, it will feel alot different but the actual time might only go down by 1/2 a second.

If you guys are going for 3.46's try a secondhand set so long as they dont have alot of k's on them they should be fine, but if your going for anything bigger 3.7, 3.9, 4.11's you'll have to go brand new as they are more prone to breaking when they end up as a second hand set.

BTW: theres a diff gear & speed ratio 'calculator' also one for changing rim and tyre size, floating around (google i think) that open up in an excel spread sheet. These 'calculators' are extremely helpful if you ever want to change your diff gears or get different rims/tyres

if you would like a copy of the 2 calculators PM me your email address ad ill send them to you

[PackaMoose]

i got a vz sv6 man and it use to hav 2.87 diff ratio but i change it to 3.46

2.87 @ 100 kmh 1800rpm in 6th
3.46 @ 100 kmh 2200rpm in 6th

i get bought 45kmh to 50 kmh out of 1st, makes a big difference to the vehicle lot of fun to drive