Best combination of diff, gearbox and engine?

[chris watton]

I am thinking ahead, after I have had the 4.3 upgrade. I know I want the CR box, but I am also wondering if it's worth changing the final drive ratio too.

From what I can gather, I think the best combination of acceleration and keeping driving flexibility (for continental drives as opposed to hill climbs..) would be a 3.73 diff and CR box. Is this about right?

I have a feeling the 3.9 diffs would be a 'mare for long journeys (but great for track days..)

Would the difference in in-gear acceleration be very noticeable from a standard 3.4 to a 3.73 diff (talking 1st-3rd gears) - Or is standard diff, CR and 4.3 good enough?

Cheers

Edited by chris watton on Tuesday 18th March 10:38

[Targarama]

I think the main choices for diff ratio are 3.54, 3.73 and 3.91. Not sure about 4.1, sounds far too low. i have 3.91 with a std gearbox on a wimpy 3.6. IMO it works perfectly. A few more rpm at motorway speeds, but never enough to bother me and have done numerous long trips with this configuration. Makes the car much more driveable in general use and a bit quicker off the mark.

For a large capacity engine with more torque you don't need this so IMO stick with the std configuration until you've tried it. I suspect the standard ratios will be pretty good with a much more torquey engine.

[WolfyJones]

chris watton said:

. I know I want the CR box,

Why?
The standard box gives better acceleration, you just need to be slick with gear changes.

[chris watton]

WolfyJones said:

chris watton said:

. I know I want the CR box,

Why?
The standard box gives better acceleration, you just need to be slick with gear changes.

...But I loved staying in 1st when pootling around town...plus I used to love the longer ratios.

Targarama said:

I think the main choices for diff ratio are 3.54, 3.73 and 3.91. Not sure about 4.1, sounds far too low. i have 3.91 with a std gearbox on a wimpy 3.6. IMO it works perfectly. A few more rpm at motorway speeds, but never enough to bother me and have done numerous long trips with this configuration. Makes the car much more driveable in general use and a bit quicker off the mark.

For a large capacity engine with more torque you don't need this so IMO stick with the std configuration until you've tried it. I suspect the standard ratios will be pretty good with a much more torquey engine.

That's is, 3.91, don't know why I wrote 4.1!

This is the last (big) job I'll have done to my Tam, so I will be with the standard set up for at least a few months after the rebuild.

[WolfyJones]

Targarama said:

I think the main choices for diff ratio are 3.54, 3.73 and 3.91. Not sure about 4.1, sounds far too low. i have 3.91 with a std gearbox on a wimpy 3.6. IMO it works perfectly. A few more rpm at motorway speeds, but never enough to bother me and have done numerous long trips with this configuration. Makes the car much more driveable in general use and a bit quicker off the mark.

For a large capacity engine with more torque you don't need this so IMO stick with the std configuration until you've tried it. I suspect the standard ratios will be pretty good with a much more torquey engine.

I had a drive in a 4 litre S car with standard box 3.9 diff last month, fk me it was quick

[chris watton]

What did the press cars use? I always assumed it would be a CR with 3.73 combo, perhaps mated to a RR engine.

[sidpinup]

chris watton said:

I am thinking ahead, after I have had the 4.3 upgrade. I know I want the CR box, but I am also wondering if it's worth changing the final drive ratio too.

From what I can gather, I think the best combination of acceleration and keeping driving flexibility (for continental drives as opposed to hill climbs..) would be a 3.73 diff and CR box. Is this about right?

I have a feeling the 3.9 diffs would be a 'mare for long journeys (but great for track days..)

Would the difference in in-gear acceleration be very noticeable from a standard 3.4 to a 3.73 diff (talking 1st-3rd gears) - Or is standard diff, CR and 4.3 good enough?

Cheers

Edited by chris watton on Tuesday 18th March 10:38

Chris,

Standard is absolutely fine and because of the extra torque you poodle in 2nd rather than 1st. You find yourself short shifting in 1st and 2nd to prevent wheel spin when having a blast so if I was you I would stick with standard and see how you get on. Just get the 4.3 and stop arseing around

[Zippee]

sidpinup said:

Chris,

Standard is absolutely fine and because of the extra torque you poodle in 2nd rather than 1st. You find yourself short shifting in 1st and 2nd to prevent wheel spin when having a blast so if I was you I would stick with standard and see how you get on. Just get the 4.3 and stop arseing around

Agreed, stock with the standard box and diff until you've tried the 4.3
I have standard and have never had any desire for a cr box, Dom also reckons the 3.4 diff is best with this engine

[M50GRF]

I've just fitted a 4.1 diff to my T350 with a 3.6ltr, It won't be on the road for a couple of weeks plus it needs to be run in for 800 miles so then we will know what it's like.
I found the 3.4diff too long geared.

I'll let you know in due course !

[WolfyJones]

chris watton said:

What did the press cars use? I always assumed it would be a CR with 3.73 combo, perhaps mated to a RR engine.

I think so, thou try and blag a ride in a standard box 3.9 car, very quick to 130/140.

[Hollowpockets]

I've got the 4.3 with CR box and 3.91 diff = FAST, the gearing is fine for longer journeys but it will use a bit more fuel being at higher revs. You know it makes sense!

[WolfyJones]

Zippee said:

Agreed, stock with the standard box and diff until you've tried the 4.3
I have standard and have never had any desire for a cr box, Dom also reckons the 3.4 diff is best with this engine

Is that also because with the standard box 3.9 Diff it might be a bit much for the engine if you are rev happy

[WolfyJones]

Hollowpockets said:

I've got the 4.3 with CR box and 3.91 diff = FAST, the gearing is fine for longer journeys but it will use a bit more fuel being at higher revs. You know it makes sense!

Have you had it on RR yet?

[Hollowpockets]

WolfyJones said:

Have you had it on RR yet?

Nope not yet, Once its had a few thousand miles on it and properly loosened up I'll put it on rollers

[chris watton]

TBH, I find 1st in completely standard guise almost redundant, and I do still miss the longer first gears.

I figured that, to get the best out of the engine, after taking certain compromises into account (motorway driving and Euro trips), the 3.73 would be the perfect sweet spot - but I shall try the CR with standard diff first, once I've had the 4.3 and it's run in.

Just trying to make my perfect Tamora...

[WolfyJones]

chris watton said:

TBH, I find 1st in completely standard guise almost redundant, and I do still miss the longer first gears.

I figured that, to get the best out of the engine, after taking certain compromises into account (motorway driving and Euro trips), the 3.73 would be the perfect sweet spot - but I shall try the CR with standard diff first, once I've had the 4.3 and it's run in.

Just trying to make my perfect Tamora...

A standard box 3.4 Diff will still do 55 mph in first,

To run a cr box 3.4 diff I would think a 4.5 or 5 litre engine with around 400 lbft is needed.

I would keep the standard box 3.4 diff combo first, should work well with 4.3 engine for what you want,

7200 revs
1 53 mph
2 79 mph
3 116 mph
4 155 mph

Edited by WolfyJones on Tuesday 18th March 13:33

[chris watton]

WolfyJones said:

chris watton said:

TBH, I find 1st in completely standard guise almost redundant, and I do still miss the longer first gears.

I figured that, to get the best out of the engine, after taking certain compromises into account (motorway driving and Euro trips), the 3.73 would be the perfect sweet spot - but I shall try the CR with standard diff first, once I've had the 4.3 and it's run in.

Just trying to make my perfect Tamora...

A standard box 3.4 Diff will still do 55 mph in first,

To run a cr box 3.4 diff I would think a 4.5 or 5 litre engine with around 400 lbft is needed.

I would keep the standard box 3.4 diff combo first, should work well with 4.3 engine for what you want,

7200 revs
1 53 mph
2 79 mph
3 116 mph
4 155 mph

Edited by WolfyJones on Tuesday 18th March 13:33

Thanks for that. Trouble is, I had a Tuscan S CR box fitted in my first (standard) Tam, and loved it - there wasn't any time or situation where I felt the 3.6 wanting - 4th and 5th were hardly ever used except for carriageways/motorways...

And....

It seems I will soon have a 3.73 Hydratrack diff anyway!

ETA - What is the difference between standard and Hydratrack?

Edited by chris watton on Tuesday 18th March 16:06

[ShiDevil]

Here's a thought..... Dom built the engine, so I presume you asked him what he would do, maybe Jason at Str8Six too given his rebuild expertise? Last time I spoke to Dom he advised on standard diff (3.43/5) and standard gearbox for a 4.3 I would only look at changing diff ratio to a 3.73 or 3.91 on a 3.6. That's purely my view and personal choice I've looked at a 3.73 as an option I would only look at a CR on a 3.91, just my view

[JRH63]

I take it that a normal diff is a 'plate' type, and a hydratrak, is a viscous unit...?

I am assuming that my 4 litre Tam, is on a std diff ratio. IMO, I would not want to shorten the gearing......

[JRH63]

But I have only had it for 5 days.........