timmus
A2OC Donor
Hi Malcyb,
Welcome to A2OC. It's clear from what you've written already, both in this thread and others, that you've been doing your homeworkbefore purchasing, which is excellent. I hope you find the right A2 for you.
This graph shows the drop in revs if you replace a TDI75's 5th gear with the 'longer 5th'...
I had the longer 5th fitted to my 5-speed 'box for a number of years, and I remain a fan of that setup despite now having a 6-speed 'box fitted in my A2. However, I'm adamant that it needs to be thought of as a change rather than as an upgrade. It's a compromise solution that provides some pros and some cons; whether or not it's suitable for you depends greatly on your use of the car.
I predominantly do motorway miles, so my previous longer 5th setup would frequently save me money due to the increase in fuel economy at motorway speeds. However, I also do a fair amount of driving in mountainous areas, where I would essentially only have 4 gears due to the longer 5th being inaccessible in such environments. In these circumstances, the longer 5th ratio would effectively cost me money. On the whole, I saved, but many A2 owners with the longer 5th find that their average fuel economy does not go up by much, if at all. Sometimes, all that's gained from the mod is a quieter drive when motorway cruising - which alone can be a good justification for the change.
Personally, I find the longer 5th is a down-grade in terms of the vehicle's 'driveability'. On a winding A-road (or in a 50mph speed limit on the motorway) I found managing the larger gap between 4th and 5th really tiresome. When doing longer cross-country routes, I found it quite draining to have to continually choose between rev'ing it harder in 4th or spluttering slightly in 5th; it requires much more concentration on an aspect of driving that's normally a subconscious process. Low-rev, high-load scenarios (such as trying to accelerate from 45mph in longer 5th) are terrible for your engine and gearbox, meaning the lower limits of the longer 5th's capabilities ought not be explored too often.
For those who use their A2 almost exclusively as a motorway cruiser, it's a very good option; compared to a 6-speed 'box, its pay-back time is relatively short and it makes driving at speed a whole lot more comfortable. But it's not without its drawbacks.
A remapped TDI75 will, without any physical modifications to the engine, happily produce 100bhp. However, without a VGT turbo, it takes a while before that 100bhp is achieved. A TDI90, with its VGT turbo, picks up quickly and delivers its torque and power across the full rev range. If performance is really important to you, there is no substitute for a TDI90. A remapped TDI90 is the only A2 that borders on being a 'hot hatch'.
Whilst the TDI75 is, by consensus, the most reliable A2 available, the TDI90 isn't far behind. As long as you're aware that your turbo and flywheel are of a more fragile design, and will raid your piggybank when they die, there's not a great deal to worry about. Whereas the FSI can be a fickle and capricious customer that may erupt in a sudden rash of problems, the TDI90's foibles are at least limited and predictable.
To answer your specific question, all the differences between the TDI75 and TDI90 are performance-orientated. There is no difference is terms of their overall refinement, noise levels, etc. They're the same engine with a few ancillary differences.
Cheers,
Tom
Welcome to A2OC. It's clear from what you've written already, both in this thread and others, that you've been doing your homeworkbefore purchasing, which is excellent. I hope you find the right A2 for you.
The TDI75 uses a 0.75 5th gear, which equates to 2580rpm at 70mph. The TDI90 uses a 0.70 5th gear, meaning the engine turns at 2407rpm at 70mph. The 'longer 5th' that some people use is a 0.66 gear, meaning 2270rpm at 70mph.
This graph shows the drop in revs if you replace a TDI75's 5th gear with the 'longer 5th'...
I had the longer 5th fitted to my 5-speed 'box for a number of years, and I remain a fan of that setup despite now having a 6-speed 'box fitted in my A2. However, I'm adamant that it needs to be thought of as a change rather than as an upgrade. It's a compromise solution that provides some pros and some cons; whether or not it's suitable for you depends greatly on your use of the car.
I predominantly do motorway miles, so my previous longer 5th setup would frequently save me money due to the increase in fuel economy at motorway speeds. However, I also do a fair amount of driving in mountainous areas, where I would essentially only have 4 gears due to the longer 5th being inaccessible in such environments. In these circumstances, the longer 5th ratio would effectively cost me money. On the whole, I saved, but many A2 owners with the longer 5th find that their average fuel economy does not go up by much, if at all. Sometimes, all that's gained from the mod is a quieter drive when motorway cruising - which alone can be a good justification for the change.
Personally, I find the longer 5th is a down-grade in terms of the vehicle's 'driveability'. On a winding A-road (or in a 50mph speed limit on the motorway) I found managing the larger gap between 4th and 5th really tiresome. When doing longer cross-country routes, I found it quite draining to have to continually choose between rev'ing it harder in 4th or spluttering slightly in 5th; it requires much more concentration on an aspect of driving that's normally a subconscious process. Low-rev, high-load scenarios (such as trying to accelerate from 45mph in longer 5th) are terrible for your engine and gearbox, meaning the lower limits of the longer 5th's capabilities ought not be explored too often.
For those who use their A2 almost exclusively as a motorway cruiser, it's a very good option; compared to a 6-speed 'box, its pay-back time is relatively short and it makes driving at speed a whole lot more comfortable. But it's not without its drawbacks.
As Bob says above, everything apart from OpenSky and climate control can be retrofitted. It is always cheaper to find a car with the optional extras that you desire already fitted, but not if that car is likely to be a money pit. Given that the youngest A2s are now 15 years old, many people choose to buy on the basis of condition and history, and then let me work my magic. Hundreds of A2s within this community have been upgraded to include the options that their owners desire.
When I built the TDI120 (documented here: https://www.a2oc.net/community/index.php?threads/tdi120-my-new-engine.32986/), the aim was to create a 1.4 TDI that uses all the most reliable bits and pieces from the various guises of that engine. Outright performance was secondary to bulletproof reliability, because that's what's most important to me. My engine is therefore based predominantly on components from the TDI75. Whilst it is probably the fastest TDI75 in the country, with 120bhp on offer, it's still no match for a remapped TDI90 (which also produces circa 120bhp).
A remapped TDI75 will, without any physical modifications to the engine, happily produce 100bhp. However, without a VGT turbo, it takes a while before that 100bhp is achieved. A TDI90, with its VGT turbo, picks up quickly and delivers its torque and power across the full rev range. If performance is really important to you, there is no substitute for a TDI90. A remapped TDI90 is the only A2 that borders on being a 'hot hatch'.
Whilst the TDI75 is, by consensus, the most reliable A2 available, the TDI90 isn't far behind. As long as you're aware that your turbo and flywheel are of a more fragile design, and will raid your piggybank when they die, there's not a great deal to worry about. Whereas the FSI can be a fickle and capricious customer that may erupt in a sudden rash of problems, the TDI90's foibles are at least limited and predictable.
To answer your specific question, all the differences between the TDI75 and TDI90 are performance-orientated. There is no difference is terms of their overall refinement, noise levels, etc. They're the same engine with a few ancillary differences.
Cheers,
Tom
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