diff gears! Does this sound about right?

[plasmid2]

Hey,

Got a quote for a 3.9:1 diff gears on a VX. The quotes I have been getting are around $1300 installed. Does this sound about right?

Also I have been told that my fuel consumption would increase. Can someone explain the physics of it all? What actually changes when having a different gear ratio and its effect on fuel consumption?

Thanks for your help.

 

[Shounak]

Quote sounds right..

 

[EXCESSV]

quote sounds right if its a LSD too.

fuel consumption goes up because the engine is reving higher in gears.
considering you dont state what type of car engine & gearbox i will explain to you from a v6 auto perspective. same princple.
the standard diff ratio is 3.08:1. you increase the amount of revs of the engine. the below is when car is in 4th gear
at 3.08:1 on 110km/hr your car is revving around 2100rpm give or take abit.
at 3.45:1 on 110km/hr your car is revving around 2500rpm give or take a bit
at 3.9:1 on 110km/hr your car revving around 3000rpm give or take a bit.

therefore from the above your engine is working nearly at 1000rpm more than standard therefore more revs = more fuel = more fuel consumption

dont forget once done you need to take it to holden or a performance place or similar where they can recalibrate your speedo coz it will be out by a lot and they need to remap your shift points coz they too will be out

Thats the end of class today kids, good luck with the test tomorrow morning :rofl:

 

[minux]

Well said Deano, unless your doing alot of track work, 3.9's are useless, 3.45 area is best

 

[plasmid2]

Thanks Deano. That makes sense. You are right I should have mentioned, my car is a V6. I don't think it has LSD.

Also, to 'minux' I have been told by some diff shops that I cant fit the 3.45 on the VX because they don't make them for the VX or something!! That didn't make sense!!

 

[minux]

Also, to 'minux' I have been told by some diff shops that I cant fit the 3.45 on the VX because they don't make them for the VX or something!! That didn't make sense!!

They may not make them in a non lsd setp, make sure they are quoting you for LSD, not a single spinner.

 

[vt1538]

Wouldn't the load change on the engine due to the diff gearing change decrease the fuel level slightly? I am not saying that the car on a whole would use less.Just that comparing two engines at the same revs with different gearing, the one with the taller gearing will need more fuel to hold the revs due to a different load.
Also as the engine VE changes with the revs, finding the point with the best efficiency should give the better fuel economy.
Just thinking out loud.

 

[EXCESSV]

at the price of $1300 i would expect it to be 3.9s with LSD.
i think the vt/vx diff housing and gearing was the same so if they still make them for vt it would be same for vx but i could be wrong.

i am gonna put 3.45 on my v6 vt after all the other mods and a singel spinner is $748 (ratio change & diff overhaul) + $110 for speedo recalibration and shift point remapping.
3.45 with LSD is $1400 (ratio change & diff overhaul) + $110 for speedo recalibration and shift point remapping.

but instead of paying $110 for the recalibration & remapping, i will get chipmaster to put chip in for $400 which will also include recalibration & remapping as well as tuning it for best performance with the bits i stick on first.

 

[plasmid2]

Deano,

So I am presuming that my VX is a 'single spinner' and I should be able to do what you want to do (3.45) for a similar price?

Let us know how you go.

 

[EXCESSV]

Deano,

So I am presuming that my VX is a 'single spinner' and I should be able to do what you want to do (3.45) for a similar price?

Let us know how you go.

unless it was optioned with LSD from factory or ppl before you put it on it will be a single spinner. put it this way. if you give it a little more gas around the corner does both wheels leave marks or one :driving: :whistling

$748 for single spinner at one place and another was $1000 so there is a variance.
car is gonna be at panel beaters for a couple of weeks.
then doing exhaust, extractors, FIT 1.9 rockers and when i gather some more money the diff ratio will be next. but putting car on dyno before & after doing exhaust, extractors, FIT 1.9 rockers.