Ciao Familia!

Searching across the internet I stumbled upon Lancia Thesis which I knew that has the same 2.4 gasoline engine as Stilo GT/Abarth, but, for my surprise, I also found out that it featured 6 speed manual gearbox! That's the thing I crave the most in my GT because most of my drives are the highways and such and while Stilo can easily reach its top speed, the revs seems way to high to keep the speed on the highway without breaking my heart over constant 4-5k RPMs.
I think (but I may be wrong badly) that both gearboxes are the C530 but simply modified variants of it and I was wondering how much of a hassle could putting this box in Stilo be?

Some could say that I should stop thinking about it and start looking for the Coupe 6spd box but man, these are rare in here (if not everywhere these days) and we have quite lots of Thesis' in Poland so that would be way, way cheaper.

Any input is highly appreciated

Little update - Stilo GT has C530.50.31 gearbox, while Lancia Thesis C530 6m + rev which says nothing particular to me.

Like you, I don't know the answer, but I found out about the Thesis 2.4 6-speed a couple of years ago. You're right, it would make such a difference to the Stilo Abarth when cruising on the highway.

I shall watch your progress with interest..!

The main question is length of gearbox and drive shafts

So after a bit of a brainstorm on Klub Fiat Stilo Poland we came to a conclusion that it definitely won't be a simple P&P conversion as the gearbox mounting that's integrated with diff housing in Stilo is (from what I understood) not existing on Thesis gearbox due to bit different gearbox/engine suspension.

I know that the whole Thesis gearbox is about 3cm wider, but no idea on driveshafts lenght. Finding any datasheets for these boxes is PITA :bang:

The topic is developing, any feedback will be appreciated <3

Longer or wider? Rear gearbox mount can be fabricated it would be such a big issue but if the box itself is 3 cm longer you could have an issue with left front wheel rubbing on the end of box

Of course I meant 3cm longer. Do you really think that 3cm longer box would already interfere with the wheel?

It depends on the offset of you rims mine standing on 16inch original wheels is not so far away from gearbox

I'm riding on original 17" alloys, but to be honest I never paid attention to how close to the box are wheels, especially when turned.

If you can source or create a 3D scan off both gearboxes.
You can then see exactly in the software e.g Autocad where any offsets are on the bell housing, CV joint and mounting connections.

That's a neat idea but to be honest I have no clue how I could get such 3D scan. There's definitely no such thing on the internet and I don't know how I could make such.

Hmmm... interesting.

First of all, find out what the final drive ratios are for the Thesis box and the Stilo box. You might find, I suspect, that the 6-speed box is not a "5-speed gearbox with an extra gear". It could well have a virtually identical final drive ratio to the Stilo 5 box.. but with closer ratios in between.. so instead of Stilo 1-2-3-4-5 you could have 0.9-1.6-2.3-3.2-4.2-5.5 for example. It could be a lot of work, just for a trivial improvement.

The Thesis is basically an Alfa 166, whereas the Stilo was an evolution of the narrower Alfa 156 platform so the Stilo might have a 5-speed box because a six speeder doesn't fit, rather than just because the Thesis is a premium car.

I would be surprised if the Thesis clutch bell-housing is vastly different to the Stilo one.. but the Thesis might have a different clutch for example, so the bell-housing might be a slightly different shape, or it may just have different mouldings for the clutch cylinder or something .. so also consider that you may need to fit the Thesis bellhousing, as well as the gearbox... And, if the Thesis does have a different hydraulic system, gear linkages etc. then you'll need to be sure you can adapt the Stilo fittings to operate those too.

But (bein optimistic) the bellhousing is likely to be identical, so the next problem will be the extra length of the gearbox. 3 cm longer isn't much.. but it's enough. The gearbox won't touch the wheel.. it's more likely to touch the inner wing... or if it clears underneath the inner wing, it could poke into the wheel arch enough to touch the suspension damper.

My money is that it will foul on the inner wing... but unless you have a box-section/crash structure/member there, all you need to do is cut a hole out of the sheet metal, so it doesn't touch the box, or more crudely, just bash it with a hammer, to put a bow in it. Any structural/box section would need to be properly angled and/or reinforced if you cut it out.

Once you have the box in there, all the hydraulics and linkages working etc. you need to make a mount to attach the gearbox to the Stilo body. The existing Stilo mount is likely to fit, if we imagine the Thesis box is "identical but a bit longer". Otherwise, the Stilo mount is the most likely to fit. See where it lines up, over the Thesis box, then mount a sandwich plate beneath the Stilo bracket and bolt that plate to the Thesis box.

Once all that's sorted out, you only have to worry about the driveshaft. If the Thesis has longer driveshafts it could be because it has a wider track. The Stilo driveshaft could fit in the Thesis differential and work fine (as well as be the right length, if Thesis has it's differential in the same place as the Stilo.

If the Thesis has a different differential arrangement to the Stilo, then the gearbox and bell-housing must also be quite different, in which case this sounds no longer a DIY job.

What you could do, if everything fails is check out the 5th speed ratio of the JTD Stilo and whether a JTD gear cog pair will fit onto the 2.4 shafts. Just swapping the two cogs for 5th gear (if they just fit on the 2.4 shafts) would give you 1-2-3-4-6 .. you'll get used to driving through the rev-range where 5th gear would normally work... and the 2.4 should be able to pull a "6th" gear ratio, when you change up from 4th.



Ralf S.

Yes I think you're right about possible fouling Ralf. I recall when I first bought my Schumi there was an awful tapping/scraping noise from the left front. Turned out to be the gearbox housing tapping againt a captive bolt welded into the nearside front chassis member. It was redundant on the Abarth, so I removed it. But it shows how tight things are down there...

If the aim is to reduce cruising revs, and if you ere prepared to lose a bit on acceleration, and perhaps slip the clutch a little when pulling away uphill with 4 or 5 on board, then an easy alternative would be to simply increase the rolling radius of the wheels by using bigger tyres.

Okay it'll make the handling a little different, but sometimes to the benefit of the drive, and not as could be suspect, to the worse.

A change from say a 215/45R17 to a 215/60R17 will give about a 10% change which would be very noticeable on cruising and motorway revs.

I've done this in the past on other cars/bikes and never had any significant detrimental issues at all.

Maxcaddy said:

If the aim is to reduce cruising revs, and if you ere prepared to lose a bit on acceleration, and perhaps slip the clutch a little when pulling away uphill with 4 or 5 on board, then an easy alternative would be to simply increase the rolling radius of the wheels by using bigger tyres.

Okay it'll make the handling a little different, but sometimes to the benefit of the drive, and not as could be suspect, to the worse.

A change from say a 215/45R17 to a 215/60R17 will give about a 10% change which would be very noticeable on cruising and motorway revs.

I've done this in the past on other cars/bikes and never had any significant detrimental issues at all.

Click to expand...

Oi, that's one way to work it around, surely. I'm not quite sure however if I'm ready for such compromises because 6 speed box could give me same acceleration (or better, depending on the specific gear ratios which could be changed) and lower cruising revs.

But I like your idea and if gearbox change fail, I will surely think about this a bit more

Baring in mind gear ratios are optimised for all applications, like going on Holiday with 4 adults, luggage, trailer, etc, the gear ratios are optimised accordingly, and 1st gear to take account of all of that, can be quite low .

Hence, say just you and a floosy do not need such a 'pull away' ratio, and upping the %'ages could be a real benefit.

Obviously if you later want to take her, her children, parents, dog etc, and a caravan, it will be a bit of a struggle

Thankfully most of the time it's only me and my lady (no floosies anymore - going to get married soon! ) and to be frank hauling more than four buttocks on board rarely happens, 3dr is useless in this aspect comparing to 5dr, not mentioning the trailer and such.

But there is a point - it's still about sacrificing some things to favour the others so it's not a perfect solution by any means. I was also thinking about switching the 5th gear ratio only buuuut the outcome would be four reasonable gears and one overdrive gear, usable only on highways, there would be also this massive revs drop between 4th and 5th so again - lots of pros and cons.
6-speed box looked like an ultimate solution for all these cons but... Ralf S. has told lots of smart things about this idea and one thing hit me - I agree with the fact that Thesis is more akin to Alfa 166, a higher tier car, but Alfa 156 also featured 5 cyl engine with 6-speed box (2.4 JTD versions).
Fiat Coupe? Same thing, 5 cyl paired with 6-speed box and Coupe has even narrower track width (1491mm to 1514mm in Stilo).
I'm helluva confused...

Maxcaddy said:

an easy alternative would be to simply increase the rolling radius of the wheels by using bigger tyres.

Click to expand...

Hmm. The Schumi is already on 18" wheels. Any bigger would look hideous in my view...

Yellow Peril said:

Hmm. The Schumi is already on 18" wheels. Any bigger would look hideous in my view...

Click to expand...

I already have flashbacks from early 2000's Pimp My Ride projects thinking about this

You could leave your 18" on but fit higher profile tyres on em. I bet tyres on 18" have thickness of a stepped-on bubble gum (if you're keeping the rolling radius the same while increasing the rim size) so put something thicker in there, like 70 instead of 30/40 profile and here you go. Rim size doesn't matter itself, it's a combination of rim size and tyre profile.

But then you're going from sporty look towards the minivan look

The problem with increasing the tyres' aspect ratio is the size of the tyre. If you go from 215/45x17 to 215/60x17, the diameter of the tyre goes up from 62cm to 69 cm... so it's 3.5cm closer to the wheel arch, and the bottom spring plate of the front damper. It may just not physically fit.

Somewhere between 215/45 and 215/60 there is probably a size (215/50?) that will not foul the damper or the wheel arch, or the wheel arch liner (ask someone to turn the front wheels from lock to lock and see how much clearance you have now) but as with the gear ratio's, it might be a lot of expense (new tyres) for just a minor improvement.

If the gearbox idea doesn't check out, then swapping the 5h gear ratio is not completely out of the window. It depends on the relative ratio between the 5th gear on your gearbox and the one on the replacement gear cogs.

I swapped the 5th gear cogs on my Alfa 145 T/Spark 1.8 to use the JTD 5th gear.
The 1.8 gearbox and the JTD gearbox just happened to have the same sized shafts and the 5th gear of the Alfa 145 gearbox is accessible under a cover, so it didn't need the gearbox removed.

Anyhow, the standard Mainshaft gear (37T) and Countershaft gear (35T) gave a Final Drive = 0.946

The Mainshaft gear of the JTD (39T) and Countershaft gear (31T) gave a Final Drive = 0.795

That dropped the rpm from 4000rpm at 80mph (indicated) to just under 3600rpm, which was useful. The 1.8 engine did feel like you were changing up from 4th to ~5.5 but in normal driving, after you get used to the sensation that you missed a gear, is actually okay. The 2.4 is more torquey still, so you'll only notice the change in engine tone, rather than acceleration.

But it depends on the gear ratios fitting onto your existing main/countershafts. The Alfa JTD box was based on the T/Spark box so that was lucky... but you need to make sure before you spend a load of money.

The only other funny part (now) is that I bought just a mainshaft cog thinking it was going be all I needed... €100 was just about worth it.. then I was sitting on the toilet looking at it.. and I realized I'd also need the countershaft cog.

So that cost me twice what I thought.... (brand new Fiat/Alfa gears, since the Alfa JTD box wasn't imported to the UK).

If you can find a cheap donor gearbox, it'll be easier to dismantle that and just see if the parts fit. Otherwise, check the part numbers for the mainshaft and countershaft.. they could be identical, in which case you'll know the JTD cogs will fit into your 2.4 gearbox. If the part numbers are different... that's not necessarily bad news... they could just be slightly longer or shorter etc. but the diameter and spline spacing may stil be identical.

Ralf S.

I took a look at the gear ratios for 2.4 and the JTD 115 version, see below:

Gear ratios (overall):
2.4:

I 3.8 (13.53)
II 2.24 (7.97)
III 1.52 (5.41)
IV 1.16 (4.13)
V 0.91 (3.24)
Final drive ratio std: 3.56



JTD:

Gear ratios (overall):

I 3.577 (12.98)
II 1.887 (6.85)
III 1.192 (4.33)
IV 0.848 (3.08)
V 0.686 (2.49)
Final drive ratio std: 3.63



Seems like a massive difference but I have no experience in such modifications so no idea how it would work out.
I think I'd be OK with using 5th as an overdrive gear because in real life, crusing around the city at 30-35mph requires driving on 4th, only outside the city I pop in the 5th, 55mph at 2500rpm.

Can I somehow imagine myself or calculate what revs I'd get throwing in the 5th from mentioned JTD gearbox?