Longer FSI 5th gear

A2Steve

A2Steve

A2OC Donor
Wales
I know a lot of members are not on the book of face, so just thought I’d share this here.

A European member has posted that they have fitted a longer 5th gear to their FSI

“part numbers on picture.

130 km/h vent from 3450rpm to 3150rpm.”

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130km/h = 81 mph

Interesting if you do a lot of motorway miles. In a nutshell the standard engine noise at 70 mph moved to 80 mph.

Andy
 
When are you going to try it Steve? I just came back from driving my FSI and think it would be great to bring down the revs a bit for motorway speeds.
 
VonB said:
When are you going to try it Steve? I just came back from driving my FSI and think it would be great to bring down the revs a bit for motorway speeds.
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I really like the FSI but if I was going to have another petrol A2 I’d be fitting another BCB engine instead.
 
Doesn't sound like a good idea to me. The FSI needs a 6th gear, not a longer 5th. This mod would just force the driver to hold 4th for longer, worsening fuel economy and refinement at lower speeds.
 
The FSI develops max torque at high revs, around 4000 rpm, so if you had a longer gear, the revs would decrease, and you'd have lower torque, and so have to change down.
You could go faster to compensate, I suppose ...
Mac.
 
How about an FSI with a 6 speed gearbox? All the benefits of getting up to speed smoothly, but cruising at lower engine rpm?


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Jellybean said:
How about an FSI with a 6 speed gearbox? All the benefits of getting up to speed smoothly, but cruising at lower engine rpm?


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I don't think any changes would work out as an improvement. The FSI's engine, and coolant maps are matched to road speed, engine speed, and engine load. Changes from one inlet mode, (stratified to homogenised, etc) to another is based on these factors. If gearbox ratios were changed, the maps would not match any of those factors. Not sure what would happen, but whatever it is, it would not be good. Maybe the European Member has ProBoost, which might help, just a guess. I'm quite happy with mine it is.
Mac.
 
PlasticMac said:
I don't think any changes would work out as an improvement. The FSI's engine, and coolant maps are matched to road speed, engine speed, and engine load. Changes from one inlet mode, (stratified to homogenised, etc) to another is based on these factors. If gearbox ratios were changed, the maps would not match any of those factors. Not sure what would happen, but whatever it is, it would not be good. Maybe the European Member has ProBoost, which might help, just a guess. I'm quite happy with mine it is.
Mac.
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Don't knock it until you've tried it!

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Jellybean said:
Don't knock it until you've tried it!

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Because of the way the FSI's engine and coolant maps work to control the mixture, engine temperature, injection pattern, and inlet air flow, using a range of parameters, including engine speed, load, and road speed. The map knows the relationship between those parameters, and they are integral to it. If you change the gear ratio, you change that relationship. The map would not work, no idea what the result would be, but probably not fun.
Since ProBoost disables much of those maps, (engine and coolant), so changing ratios might not be a problem in that case.
Mac.
 
Member - Petra had an fsi with a 6 speed gearbox fitted by Tony and conversion from Germany and by all accounts it was a joy to drive. If it equates to as Andrew mentions 80mph would be same noise level as 70mph that would be a big bonus. Imagine how quiet it would be cruising at 70mph but noise levels of 60mph, very quiet. I'm not sure a 6 speed gearbox would effect the maps all that much. All you're doing is swapping to lower revs with a 6th gear to within the parameters of the 5th speed gear, the only difference would be a potential greater speed therefore wind rush into the bonnet area - yes / no ?
 
A six speed conversion, where the gear ratios of 1 - 5 were close to the original, with a longer 6th sounds like an ideal setup. As you say, maps would probably be fine.
Mac.
 
PlasticMac said:
A six speed conversion, where the gear ratios of 1 - 5 were close to the original, with a longer 6th sounds like an ideal setup. As you say, maps would probably be fine.
Mac.
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Ah, so now you've changed your tune!
Thought you had a million reasons why it was a bad idea?

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Vorsprung durch Technik said:
Member - Petra had an fsi with a 6 speed gearbox fitted by Tony and conversion from Germany and by all accounts it was a joy to drive. If it equates to as Andrew mentions 80mph would be same noise level as 70mph that would be a big bonus. Imagine how quiet it would be cruising at 70mph but noise levels of 60mph, very quiet. I'm not sure a 6 speed gearbox would effect the maps all that much. All you're doing is swapping to lower revs with a 6th gear to within the parameters of the 5th speed gear, the only difference would be a potential greater speed therefore wind rush into the bonnet area - yes / no ?
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Exactly. I have that car.

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