Rear differential ratios

[MaxRothery]

Hi there I could do with some help

I've been looking into doing some stupid things to my car and need some help with ratios. I'm looking for cars that are rear wheel drive and with one of the following ratios:
3.27
3.45
3.63
3.89
4.1/4.11

I know that the triumph dolomite has these ratios, but I'm looking for an IRS diff

Thank you
Max

[stevieturbo]

MaxRothery said:

Hi there I could do with some help

I've been looking into doing some stupid things to my car and need some help with ratios. I'm looking for cars that are rear wheel drive and with one of the following ratios:
3.27
3.45
3.63
3.89
4.1/4.11

I know that the triumph dolomite has these ratios, but I'm looking for an IRS diff

Thank you
Max

I'd guess you dont need all of them ? And if you're suggesting a Triumph, presumably you dont need the likes of a Ford 8.8 or 9" that will support 1000+ ?

What exactly do you need ?

[MaxRothery]

stevieturbo said:

MaxRothery said:

Hi there I could do with some help

I've been looking into doing some stupid things to my car and need some help with ratios. I'm looking for cars that are rear wheel drive and with one of the following ratios:
3.27
3.45
3.63
3.89
4.1/4.11

I know that the triumph dolomite has these ratios, but I'm looking for an IRS diff

Thank you
Max

I'd guess you dont need all of them ? And if you're suggesting a Triumph, presumably you dont need the likes of a Ford 8.8 or 9" that will support 1000+ ?

What exactly do you need ?

Basically, I'm looking into making my car, which is a triumph 1500tc, AWD. And in an attempt to keep its registration plate and documents as a modified car, I'll be keeping the rear axle as standard, which are the ratios above. I'm looking for the centre section, the diff, of an IRS system with the Sam ratios do I don't have to swap the rear to IRS to make the ratios match. It would only need to withstand about 400ish hp as I won't be exceeding that

[DrTre]

The 5 speed mx5 torsens is 4.1, the six speed is 3.9.

They handle north of 300bhp but 400 i know not.


Edit: that sounds a lot of fun of a project, what spurred that?

Edited by DrTre on Thursday 1st October 14:08

[stevesingo]

BMW Medium(188) case come in the following:

3.25
3.46
3.64
3.91
4.10

And more.

LSDs available too.

[MaxRothery]

stevesingo said:

BMW Medium(188) case come in the following:

3.25
3.46
3.64
3.91
4.10

And more.

LSDs available too.

So close, should really be the exact same so that the rear doesn't force it's way forward. I've seen a pdf containing lots of diff ratios, these ratio seems to be an old style, the most common manufacture with those ratios was ford. Mercedes 280 had a the same ratio but the centre diff was like £1200. Toyota did a few in the 80's matching some but I can't remember what ratio it was

[stevieturbo]

MaxRothery said:

Basically, I'm looking into making my car, which is a triumph 1500tc, AWD. And in an attempt to keep its registration plate and documents as a modified car, I'll be keeping the rear axle as standard, which are the ratios above. I'm looking for the centre section, the diff, of an IRS system with the Sam ratios do I don't have to swap the rear to IRS to make the ratios match. It would only need to withstand about 400ish hp as I won't be exceeding that

So again, what rear diff do you have ? you wont be using all of those ratios ?

It sounds like you're saying you're keeping the rear axle, but then you're changing the rear diff ? Then you're swapping to an IRS ? Is the current rear axle IRS or a live axle ?

What are you using for a gearbox/transfer and front diff ?

I'd think your easiest option would just get a 4wd system from a Sierra or something.

[MaxRothery]

stevieturbo said:

MaxRothery said:

Basically, I'm looking into making my car, which is a triumph 1500tc, AWD. And in an attempt to keep its registration plate and documents as a modified car, I'll be keeping the rear axle as standard, which are the ratios above. I'm looking for the centre section, the diff, of an IRS system with the Sam ratios do I don't have to swap the rear to IRS to make the ratios match. It would only need to withstand about 400ish hp as I won't be exceeding that

So again, what rear diff do you have ? you wont be using all of those ratios ?

It sounds like you're saying you're keeping the rear axle, but then you're changing the rear diff ? Then you're swapping to an IRS ? Is the current rear axle IRS or a live axle ?

What are you using for a gearbox/transfer and front diff ?

I'd think your easiest option would just get a 4wd system from a Sierra or something.

What I'm trying to concoct is using the triumph rear live axle, which can have any of those given ratios, and use an IRS rear diff, out of say a Subaru, which has the same ratio as one of the given ratios.

I'll think of something for the transfer box

[ouninpohja]

The Ford 7 inch diff is available in 3.63 ratio

[wildoliver]

I'm totally confused as to what your doing with this irs diff? Is it going in the back in which case how are you going to put that in the middle of a live axle, go in the front in which case where are you putting the engine or putting it in the centre in which case why?

[stevieturbo]

MaxRothery said:

What I'm trying to concoct is using the triumph rear live axle, which can have any of those given ratios, and use an IRS rear diff, out of say a Subaru, which has the same ratio as one of the given ratios.

I'll think of something for the transfer box

OOOOOOOOKKKKKKKKKKK..

So you want to fit this....



into something like this ?




Can you see a slight problem there ??

[MaxRothery]

stevieturbo said:

MaxRothery said:

What I'm trying to concoct is using the triumph rear live axle, which can have any of those given ratios, and use an IRS rear diff, out of say a Subaru, which has the same ratio as one of the given ratios.

I'll think of something for the transfer box

OOOOOOOOKKKKKKKKKKK..

So you want to fit this....



into something like this ?




Can you see a slight problem there ??

No, no, I don't mean to use the IRS diff inside the live axle, I want to use the IRS rear diff to power the front wheels and the live axle to power the rear wheels

[stevieturbo]

Finally some sense !!!

It would have been a lot easier to state that from the outset.

Subarus are fairly readily available in 3.54, 3.9, 4.1 and 4.44

Sierra 4x4's usually 3.62 although think some 2.0 n/a 4x4's used 3.92

Full range for the rear section only is a little wider

[MaxRothery]

stevieturbo said:

Finally some sense !!!

It would have been a lot easier to state that from the outset.

Subarus are fairly readily available in 3.54, 3.9, 4.1

Is the Subaru ratio 4.1, 4.11, or 4.111 as I've seen all three when looking through the forums. As I think triumph did a 4.1 and a 4.11 as rimmerbros sell both a 4.1 and a 4.11

[stevieturbo]

MaxRothery said:

Is the Subaru ratio 4.1, 4.11, or 4.111 as I've seen all three when looking through the forums. As I think triumph did a 4.1 and a 4.11 as rimmerbros sell both a 4.1 and a 4.11

Really doesnt matter a damn.

Worn tyres or driving around a corner would create more of a difference than what you're talking about.

[MaxRothery]

stevieturbo said:

MaxRothery said:

Is the Subaru ratio 4.1, 4.11, or 4.111 as I've seen all three when looking through the forums. As I think triumph did a 4.1 and a 4.11 as rimmerbros sell both a 4.1 and a 4.11

Really doesnt matter a damn.

Worn tyres or driving around a corner would create more of a difference than what you're talking about.

Oh ok

Thanks Steve

[wildoliver]

Ok so I'm assuming your going to use the fwd triumph hubs which I assume bolt up to your suspension given the similarities of the 2 cars.

Then make the drive shafts to adapt from those hubs to the diff.

Where are you going to put the diff though? There is an engine in the way. Even if you ignore the glaring problem of a couple of hundred kilos of cast iron being inconveniently located exactly where the diff wants to occupy (actually that's unfair it's mostly the sump that's in the way so possibly take the 2 centre cylinder pistons and rods out and get the crank cut and welded to remove the crank throws for those 2 cylinders and run it as a 2 cyl! ) You still have to overcome the not inconsiderable problem of splitting drive to front and rear from a gearbox that was never produced in 4wd form.

If for some intensely masochistic reason you decide you really must have this car 4wd your best bet is to implant an existing 4wd drive train out of something like a Subaru Justy, it will be no slower and might actually work. Not as well as the Subaru Justy but it should function.

I'm all for ambitious projects and I hate trying to talk sense as I love an absurd project like no-one else but this project is at best doomed to failure, at worst you might actually succeed and produce the slowest poorest handling least useful 4wd vehicle ever.

[MaxRothery]

wildoliver said:

Ok so I'm assuming your going to use the fwd triumph hubs which I assume bolt up to your suspension given the similarities of the 2 cars.

Then make the drive shafts to adapt from those hubs to the diff.

Where are you going to put the diff though? There is an engine in the way. Even if you ignore the glaring problem of a couple of hundred kilos of cast iron being inconveniently located exactly where the diff wants to occupy (actually that's unfair it's mostly the sump that's in the way so possibly take the 2 centre cylinder pistons and rods out and get the crank cut and welded to remove the crank throws for those 2 cylinders and run it as a 2 cyl! ) You still have to overcome the not inconsiderable problem of splitting drive to front and rear from a gearbox that was never produced in 4wd form.

If for some intensely masochistic reason you decide you really must have this car 4wd your best bet is to implant an existing 4wd drive train out of something like a Subaru Justy, it will be no slower and might actually work. Not as well as the Subaru Justy but it should function.

I'm all for ambitious projects and I hate trying to talk sense as I love an absurd project like no-one else but this project is at best doomed to failure, at worst you might actually succeed and produce the slowest poorest handling least useful 4wd vehicle ever.

Engine location problem solution 1: was thinking about doing similar to what Nissan did with the GTR, and to run the half shafts under the engine. the engine im looking to swap in, the sump needs to be remodeled anyway to fit over the cross member,so if i made the sump low profile, the half shafts would go under.

Engine location problem solution 2: use the sump and mount the diff straight to it, this was more if i used a subaru diff as its just 6 holes, would be like IRS but with the diff a little lower than usual.

Splitting the driveline solution: use a transfer box from either a jeep or something similar. mount it either horizontally and rework the transmission tunnel to suit, or hang it low and to the side and have it hang low underneath the car

front hubs: either use triumph FWD hubs if i can find them, their like hens teeth. or id get some new, custom ones as that would be easier.

simple solution: use the V6 and 4x4 gearbox from a Ford grenada, the I4 and 4x4 gearbox from a sierra, (if it can fit, RB20det with a GTR sump), use CV joints and connections and create spacer to adapt to triumph FWD hubs.

[stevieturbo]

I think you're very much underestimating the work involved.

But yes the most sensible solution as already said is to get an entire drivetrain from a 4wd car and use those parts as much as possible.

[MaxRothery]

stevieturbo said:

I think you're very much underestimating the work involved.

But yes the most sensible solution as already said is to get an entire drivetrain from a 4wd car and use those parts as much as possible.

Yeah, I'm very much under estimating the work involved. I've just been on the Triumph forums as apparently, triumph did a 4WD triumph 1500 so it is possible to do with all triumph parts as the gearbox is still available to buy