Changing the differential to a 3.91
Discussion
I have now ruled out a supercharger due to cost and I am now considering what to me at least seems the next best thing and change the diff to a 3.91 I am beginning to find the acceleration rather lazy and reading other threads the diff change will give the car a more urgent feel.
I have no understanding about what a 'final drive' is or what it does. All I know is that it improves acceleration somehow and you rev higher for a given speed. Is every gear effected or just some gears?
Can anyone explain what and how any benefits are achieved by changing the diff to a 3.91 and is this a very labour intensive operation, i.e is it something that can be done in a day
I have no understanding about what a 'final drive' is or what it does. All I know is that it improves acceleration somehow and you rev higher for a given speed. Is every gear effected or just some gears?
Can anyone explain what and how any benefits are achieved by changing the diff to a 3.91 and is this a very labour intensive operation, i.e is it something that can be done in a day
Pretty much just increases torque due to gearing at the rear wheels.
Of course in all gears. Its not bad, makes the car feel more responsive but you run out of rpm faster.
If you plan to mod later down the line Id avoid it as it will compound traction issues.
If you are on a budget and staying stock then go for it
Of course in all gears. Its not bad, makes the car feel more responsive but you run out of rpm faster.
If you plan to mod later down the line Id avoid it as it will compound traction issues.
If you are on a budget and staying stock then go for it
If your not going supercharged, its the best thing you can do!!
To put it in prespective, a 3.9 diff in a CV8 gives you gearing not all that different from a VXR8. Thats why VXR8's are so much quicker on acceleration, its all in the gearing. Power only went up a bit over monaro and so did weight, but they are still quicker.
To put it in prespective, a 3.9 diff in a CV8 gives you gearing not all that different from a VXR8. Thats why VXR8's are so much quicker on acceleration, its all in the gearing. Power only went up a bit over monaro and so did weight, but they are still quicker.
nosubstitute said:
Roger
How long would you need the car for to fit the 3.91 diff? Is this something I could wait for as I have done with my headers and catback?
How long would you need the car for to fit the 3.91 diff? Is this something I could wait for as I have done with my headers and catback?
If we do a diff in advance, so effectively an exchange, then we can do the same day. If we rebuild yours, there is a risk it may overrun to a 2nd day. Price is the same either way.
Changing the diff from 3.46 to 3.91 is 13% lower so you get 13% extra shove in the back. As you run out of revs 13% sooner you actually get up through the gears 26% faster - increasing the subjective improvement.
The earlier version of the gearbox you have is not really suited to cars as heavy as the Monaro with 1st to 4th being unusually close. Much more at home in the Dodge Viper and Corvette. The factory improved later cars by using a different version of the gearbox with a wider ratio spread 1st to 4th, more similar to other manual cars. Vauxhall messed up so UK CV8s didn't benefit only the VXRs did.
I changed my CV8 myself. More expensive than doing the diff but the ratio spread is better and doesn't need the speedo recalibrating. So my car is now the same as an Australian CV8.
I'm sure Monkfish would offer gearbox swaps if they could get the boxes for sensible money which presumably they can't. I was lucky and found one on eBay USA, personally importing it myself.
The earlier version of the gearbox you have is not really suited to cars as heavy as the Monaro with 1st to 4th being unusually close. Much more at home in the Dodge Viper and Corvette. The factory improved later cars by using a different version of the gearbox with a wider ratio spread 1st to 4th, more similar to other manual cars. Vauxhall messed up so UK CV8s didn't benefit only the VXRs did.
I changed my CV8 myself. More expensive than doing the diff but the ratio spread is better and doesn't need the speedo recalibrating. So my car is now the same as an Australian CV8.
I'm sure Monkfish would offer gearbox swaps if they could get the boxes for sensible money which presumably they can't. I was lucky and found one on eBay USA, personally importing it myself.
porrohman said:
Magic919 said:
Some 15's would do it :-))
Lol, Now that would look funny.www.mandhtires.com/store.php?crn=70&rn=290&action=show_detail
not if you stuck a set of these on and smoked everyone off the line at the strip
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