Taller Final Drive ratio

[Bjorn Nilson]

I am very happy with the result of my UT engine build. It works well on track and with X1/9 5 speed gear box/gear ratios I can keep it within maximum torque range 4-7000 rpm in most situatons. However, this is mainly a street car so I am looking for making the final drive taller, more like standard UT 3.588:1 instead of X1/9's 4.077:1.
I also have an UT Mk2 gear box but it doesn't fit the UT Mk1 (or X1/9) engine. -The input shaft/splines differs.
I have an idea to move the final drive from the UT box to the X box. But does the pinion and crown wheel from the UT Mk2 box fit in the X box? I also read in the forum that pinion/crown wheel from Ritmo/Strada/Regata would work? But they have the same ratio as X? I've been searching the web for Final Ratio Gear Kits, but all I've found are shorter than stock 4.077:1, most likely best for tuned, high revving X1/9's and hill climb.
I am also thinking about having a Torsen diff made for VAZ Samara. But that will require some modifications a described at https://www.villevieri.com/egbox.htm .Has this been done by any member in the forum?
Any feedback would be appreciated.
EDIT: Forgot to add the UT/X ratio comparison sheet that may be of interest:

 

[Dr.Jeff]

A couple years ago I researched the options for a limited slip diff in the X gearbox. Honestly I don't recall for sure but I believe I found that the Mk2 UT diff unit was different from the X's (and therefore I assume the Mk1 UT as well) and cannot be installed. There are others here that will know for sure. However regarding the Samara diff conversion, did you see where we discussed that not long ago?
The Samara diff discussion starts on post #19, but there might be other useful info in the thread for you:

Torque with LSD in X1/9 5 speed

Can anyone on xweb with a good understanding of limited slip diffs help me understand the torque loads on the diff carrier itself. As most know, the diff carrier in the 5 speed transmission is a weak point in fast launches with sticky tires and a good amount of power and torque from a modified...

xwebforums.com

Also don't forget you can change the final drive ratio by installing taller rear tires.

 

[Dan Sarandrea (Phila)]

I seem to recall that a popular mod in the UK was to install UT transaxle internals into X1/9 cases in the belief that said UT internals were made to stand up to greater power therefore would live longer that a stock unit in an X1/9, especially if said X1/9 had any upgrades that increased engine output.

Now, whether or not that was UT Mk1 or Mk2 or what, I don't recall that ever being extensively discussed.

Now for an unsolicited opinion! From my armchair I never really considered that, in and of itself, changing a stock 5 speed X to use a higher final drive ratio to be a good move from a cost benefit analysis. Sourcing and paying for this mod's increasingly rare parts, the labor involved in dropping the trans, opening it up, and the inevitable mission creep (yeah I dare you to not replace anything but the ring gear and shaft while you have the trans apart--go ahead and make my day LOL), and then putting it all back together to save 300-400 rpm at typical USA highways speeds. OTOH if your trans is tired or toast and you were going to have Steve H build you a box and Steve said, "Hey if you want to go with a taller final drive I have the parts to do that and it'll only add this much to the total bill," then yeah it would be worth considering at that point.

 

[Ulix]

The UT Mk1 parts fit and would probably be the way to go.
4th gear will be exactly what your 5th gear is now.
So quite a change.

I don‘t know about Mk 2.

 

[Bjorn Nilson]

I seem to recall that a popular mod in the UK was to install UT transaxle internals into X1/9 cases in the belief that said UT internals were made to stand up to greater power therefore would live longer that a stock unit in an X1/9, especially if said X1/9 had any upgrades that increased engine output.

Now, whether or not that was UT Mk1 or Mk2 or what, I don't recall that ever being extensively discussed.

Now for an unsolicited opinion! From my armchair I never really considered that, in and of itself, changing a stock 5 speed X to use a higher final drive ratio to be a good move from a cost benefit analysis.

I agree, but my situation is as follows.
When I bought the fully overhauled UT engine the deal also included a X1/9 gearbox of unknown condition. The seller told me it should be ok, but he didn't promise. I did my best to check it, and all gears worked so I gave it a good clean up, filled it with Redline MTL and put it in the car together with the UT engine. I hoped for that this was a better option than overhauling the gearbox from my 1500 X as that one was leaking and with synchros not in perfect condition. Without starting or driving the car the "new" gearbox suddenly locked. Only 5th and R could go in position. To have the car for dyno I put my old leaking gearbox in the car to have it running before the end of the season.
I also realize that a LSD is needed to handle 205 whp and 267 wNm from the UT engine. So I need to tear it down anyway. -A nice planned winter project. Why spend the time in the armchair when I have a garage.
What I've heard the UT Mk1 gearbox internals are compatible with X1/9 5 Speed. Unfortunately I have the UT Mk2 gearbox and that might be a compability issue. That's why I started this thread.

 

[Dr.Jeff]

I have the UT Mk2 gearbox and that might be a compability issue.

And that was what I was referring to; I believe (but not sure) that I found out the Mk2 is not compatible with the X, at least in terms of swapping internal components such as the diff. But that needs to be verified. I'll bet @rachaeljf will know.

 

[GregS]

I can confirm the Uno Turbo mk2 box crownwheel and pinion will not fit in the X1/9 gearbox, the diff is also different. The Uno mk1 box will fit, but only the early ones up to about mid to late 1987, then they changed to the later C510 box that was used in the mk2 turbo, Tipo etc. Some Regata/Strada/Ritmo used the same or similar final drive ratio as the Uno mk1, some also used 3.21:1

 

[Bjorn Nilson]

I can confirm the Uno Turbo mk2 box crownwheel and pinion will not fit in the X1/9 gearbox, the diff is also different. The Uno mk1 box will fit, but only the early ones up to about mid to late 1987, then they changed to the later C510 box that was used in the mk2 turbo, Tipo etc. Some Regata/Strada/Ritmo used the same or similar final drive ratio as the Uno mk1, some also used 3.21:1

Thanks for info. So it is the famous C510 I have on the garage floor. It looks more rigid than the X1/9 gearbox. Unfortunately the input shaft doesn't fit the engine either, so there is no way to use this unit with current setup. I paid only1000 SEK (100 USD) for it so I can live with it.

 

[GregS]

Thanks for info. So it is the famous C510 I have on the garage floor. It looks more rigid than the X1/9 gearbox. Unfortunately the input shaft doesn't fit the engine either, so there is no way to use this unit with current setup. I paid only1000 SEK (100 USD) for it so I can live with it.

Well, it is possible to fit it to an X1/9, it's been done in Australia. The C510 is a much stronger gearbox but it takes some work, from memory, cable gear linkage and more.

 

[myronx19]

The Mk1 UnoT gearbox is essentially the same as the X1/9 - except it has different ratios, and it has needle bearings on 3rd & 4th (and others? not sure).

I would not say that the Mk1 is any stronger than the X1/9 - it's just as weak by design (except the reverse shaft is most likely of larger diameter as the later gearboxes). To add to that, parts are even harder to find!

Ideally - a final drive from a Fiat Strada (or Ritmo) would do the trick. It's an easy swap. You just need the pinion shaft and ring gear at minimum. This will give you a 3.59:1 ratio. Now... finding a Ritmo/Strada gearbox isn't easy. I bought one - already planning for the idea that the taller final drive will help with the UnoTurbo.

The transmission will be the weak point - but I'll be gentle

The Mk2 UnoT gearbox is quite different than the Mk1 - it's the "top change box" and would require totally different shift linkages. From memory, nothing inside that box can fit into the X1/9 box - not 100% sure about that, but I've read that over on the FUTOC page.

 

[GregS]

This list of models that used the X1/9 type transmissions will give an idea what ratios are used in what models. Front wheel drive has a different case with the shift rod in the opposite side to the X1/9. Input shaft is longer in Regata 100S and Ritmo 105TC. I have a crown wheel and pinion shaft from a Regata 100S that I don't need, so it is probably 3.211:1, and shipping from Australia wouldn't be cheap.

 

[Dr.Jeff]

Unfortunately the input shaft doesn't fit the engine

Is there any chance of modifying the input shaft to fit? I have no idea how they differ so that may not be a sound idea, and if I'm understanding correctly there may be other reasons why that trans won't be easy to install. But just a thought.

 

[Bjorn Nilson]

Is there any chance of modifying the input shaft to fit? I have no idea how they differ so that may not be a sound idea, and if I'm understanding correctly there may be other reasons why that trans won't be easy to install. But just a thought.

Seems to be easier than I thought actually. An UT Mk2 clutch friction plate with correct diameter and number of splines would do the trick. Currently I have the X1/9 and C510 boxes side by side and they do not differ much. The C510 gearbox seems to mate quite well with the engine but a small mod for the lower engine mount is necessary. The stub shafts look the same on both gear boxes. Biggest concern is the gear selector linkage that must be converted to wires to work with the C510.
I got the C510 very cheap so I will keep it. Maybe I will start a project when I trashed my two other X1/9 gearboxes . I also found a 4th box. -A Ritmo (Strada) 85S gearbox so I have covered up for eventual future disasters. I even got the taller final drive I wanted with it.
Last year I met a Norwegian guy at the race track. He has a super fast Dallara style Exxie currently with a 1.4l Abarth engine. He has long experience with Fiat SOHC engines and he meant that the C510 gearbox would fit both X1/9 1.5l and UT Mk1, and now I believe him. He even told me the 6 speed box from a modern Abarth 595 would work with minor(?) modifications.

 

[GregS]

I have corrected my earlier post about requiring new axles, the x1/9 5 speed ones do fit. As well as the other changes you mentioned you will also need a clutch slave cylinder to match.

 

[Ulix]

Bjorn, thanks for the research.

Is the C510 stronger than the X transmission?

 

[GregS]

Yes, much stronger. I have no personal experience, but have heard they are good for 300hp. They are used in 500 Abarths, and many Alfas and Fiats. There also are a range of LSDs available.

 

[Bjorn Nilson]

Bjorn, thanks for the research.

Is the C510 stronger than the X transmission?

Oops. This didn't post due to system backup it seems. But anyway....

I've heard it should be stronger and that is probably true. I haven't opened it yet but externally it seems to have more meat and a slightly different casting that definitely brings more rigidity to the box. The input shaft is thicker with 22 splines so most likely the internals are bigger too.

 

[myronx19]

Is the C510 stronger than the X transmission

It's certainly a better design - C510 uses needle bearings instead of bushings on the driven gears (less drag torque), better synchronizer ring design (including pre-engagement/blocker rings) over the Porsche blockers for 3/4/5 X1/9 style - and the C510 is designed to carry more torque.

I had a C510 in my Abarth 500. It shifted nicely, but mine developed an input shaft leak and one of the axle seals also developed a leak. Redline now makes a fluid that's compatible with the OE fluid called MT-LV for use in the C510. It doesn't take much fluid, so leaks aren't good! - either way, subjectively - it seemed quite durable.

Does a late model Abarth 500 C510 mount to an X1/9 block? I don't think it does - the starter motor is on the wrong side - and also, it doesn't have a regular clutch throwout arm (it has a concentric slave cylinder on late model C510)

I'm rebuilding my 5spd right now - yikes... the parts are NOT cheap!

 

[Dr.Jeff]

mine developed an input shaft leak and one of the axle seals also developed a leak

Imagine that, an Italian car that leaks.

Does a late model Abarth 500 C510 mount to an X1/9 block?

I vaguely recall someone saying something about this previously, that it will not fit. But wouldn't that be nice, to have a good option for a more robust trans. And you are right, parts for the X's box are becoming become harder to find and very expensive. All the more reason to look into substitutes for the whole thing.

 

[Dr.Jeff]

Seems to be easier than I thought actually. An UT Mk2 clutch friction plate with correct diameter and number of splines would do the trick. Currently I have the X1/9 and C510 boxes side by side and they do not differ much. The C510 gearbox seems to mate quite well with the engine but a small mod for the lower engine mount is necessary. The stub shafts look the same on both gear boxes. Biggest concern is the gear selector linkage that must be converted to wires to work with the C510.
I got the C510 very cheap so I will keep it. Maybe I will start a project when I trashed my two other X1/9 gearboxes . I also found a 4th box. -A Ritmo (Strada) 85S gearbox so I have covered up for eventual future disasters. I even got the taller final drive I wanted with it.
Last year I met a Norwegian guy at the race track. He has a super fast Dallara style Exxie currently with a 1.4l Abarth engine. He has long experience with Fiat SOHC engines and he meant that the C510 gearbox would fit both X1/9 1.5l and UT Mk1, and now I believe him. He even told me the 6 speed box from a modern Abarth 595 would work with minor(?) modifications.

Switching the shift mechanism to a cable system might not be a bad idea anyway. Frankly the stock system isn't the greatest design in my opinion. And if the C510 box can be utilized it would certainly be worth it, especially with your increased power. Plus like Greg said, there's lots more options for upgrades (e.g. LSD) if desired.
How do the gear ratios / final drive in the C510 compare to those in the Ritmo box?