The engine revs at 70mph in top gear (6th on TA or fifth on the MJ) are practically the same with the TwinAir and the MultiJet diesel — around 2800rpm.
The six speed TA 4x4 gearbox has (essentially) the same five upper gears as the MJ plus a super-low first to compensate for the lower amount of torque the TA 4x4 has for slow speed off road manoeuvres.
So, it would be a useless bottom gear on an MJ, and lead to a lack of low-end grunt on the TA… bad result either way
They are not the same at the top end.
They are very similar in 1st - 5th but there is quite a difference between 6th in the 6speed box and 5th in the 5speed diesel box.
looks something like this
| Engine | | Panda Twinair Gear Ratios | MPH | Panda 1.3 Multijet Gear Ratios | MPH |
| RPM | 1st | 4.1 | 12.77 | 4.273 | 12.53 |
| 2800 | 2nd | 2.158 | 24.26 | 2.238 | 23.93 |
| 3rd | 1.345 | 38.93 | 1.444 | 37.09 |
| 4th | 0.974 | 53.76 | 1.029 | 52.05 |
| 5th | 0.766 | 68.36 | 0.767 | 69.83 |
| 6th | 0.646 | 81.06 | | |
| | | | | |
| Final | 3.818 | | 3.733 | |
So at 2800RPM in 6th you are doing 81mph and assuming the same tire size in the diesel you are doing 70mph at the same RPM
the 6th speed in the petrol is clearly to try and offer a little better economy otherwise at 3000 RPM to do 70mph the petrol car would be using a considerable amount more fuel than a 5 speed, not so it is very likely done to keep the petrol within emissions standards.
The diesel puts out far less CO2 so far less of a concern if it is doing 3000 RPM. But I am pretty sure if Fiat could have done a 6 speed in the Diesel they would have, as it would have brought down engine revs and resulted in a more comfortable ride at motorway speeds.
Having thought about this a little more I think there are a few issues that meant that they didn't put a 6cog on a multijet 4x4.
Torque. The torque of the diesel (which is actually 90% more than the petrol to correct my previous statement) would potentially damage the TwinAir gear box. but assuming that the twinair just used a 6speed gearbox from something else the next issue would be.....
Fitment. The Twinair engine is a very different engine to fiat's 1.3 multijet. The multijet is more akin to the Fire engine, I believe the multijet was modified from the Fire engine, however the Twinair was a totally "new" engine thats not to say they didn't design the fitment of the gearbox to be compatible with existing gearboxes but it does then lead me to my next point which is.......
Placement. all evidence would suggest with the Twinair being a narrower engine means that it is placed in the engine bay more over to the offside of the engine bay, moving the gearbox more centrally to the engine bay. The Multijet and other Fire engine equipped cars have an intermediate shaft from the gearbox to the off side, to get the drive shaft power out passed the engine block, but with the twinair being much narrower and the gearbox moving more centrally the TwinAir doesn't need an intermediate shaft it has two similar drive shafts straight from the box to the wheels.
The whole setup allows for more space in the engine bay on the nearside (uk layout) and I remember that 6 speed gearboxes in fiat's tend to be wider as the 6 gear is in essence bolted on the end of the gearbox.
This is why the Abarth 500's did not come with a manual 6 speed gearbox and it was only in 2015 they offered a 6 speed in an automatic (different design) gearbox.
I think any 6 speed in a panda engine bay if mated to the end of a 4 cylinder engine, would protrude quite significantly into the nearside wheel well.
This video shows the difference in size on a 5 - 6speed gearbox change, there is quite a lot of extra width on the 6 speed.
